| Message ID | 20250322001306.41666-4-okorniev@redhat.com (mailing list archive) |
|---|---|
| State | Under Review |
| Delegated to: | Chuck Lever |
| Headers | show |
| Series | access checking fixes for NLM under security policies | expand |
On Sat, 22 Mar 2025, Olga Kornievskaia wrote: > NLM locking calls need to pass thru file permission checking > and for that prior to calling inode_permission() we need > to set appropriate access mask. > > Fixes: 4cc9b9f2bf4d ("nfsd: refine and rename NFSD_MAY_LOCK") > Signed-off-by: Olga Kornievskaia <okorniev@redhat.com> > --- > fs/nfsd/vfs.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c > index 4021b047eb18..7928ae21509f 100644 > --- a/fs/nfsd/vfs.c > +++ b/fs/nfsd/vfs.c > @@ -2582,6 +2582,13 @@ nfsd_permission(struct svc_cred *cred, struct svc_export *exp, > if ((acc & NFSD_MAY_TRUNC) && IS_APPEND(inode)) > return nfserr_perm; > > + /* > + * For the purpose of permission checking of NLM requests, > + * the locker must have READ access or own the file > + */ > + if (acc & NFSD_MAY_NLM) > + acc = NFSD_MAY_READ | NFSD_MAY_OWNER_OVERRIDE; > + I don't agree with this change. The only time that NFSD_MAY_NLM is set, NFSD_MAY_OWNER_OVERRIDE is also set. So that part of the change adds no value. This change only affects the case where a write lock is being requested. In that case acc will contains NFSD_MAY_WRITE but not NFSD_MAY_READ. This change will set NFSD_MAY_READ. Is that really needed? Can you please describe the particular problem you saw that is fixed by this patch? If there is a problem and we do need to add NFSD_MAY_READ, then I would rather it were done in nlm_fopen(). Thanks, NeilBrown > /* > * The file owner always gets access permission for accesses that > * would normally be checked at open time. This is to make > -- > 2.47.1 > >
On Thu, Mar 27, 2025 at 7:54 PM NeilBrown <neilb@suse.de> wrote: > > On Sat, 22 Mar 2025, Olga Kornievskaia wrote: > > NLM locking calls need to pass thru file permission checking > > and for that prior to calling inode_permission() we need > > to set appropriate access mask. > > > > Fixes: 4cc9b9f2bf4d ("nfsd: refine and rename NFSD_MAY_LOCK") > > Signed-off-by: Olga Kornievskaia <okorniev@redhat.com> > > --- > > fs/nfsd/vfs.c | 7 +++++++ > > 1 file changed, 7 insertions(+) > > > > diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c > > index 4021b047eb18..7928ae21509f 100644 > > --- a/fs/nfsd/vfs.c > > +++ b/fs/nfsd/vfs.c > > @@ -2582,6 +2582,13 @@ nfsd_permission(struct svc_cred *cred, struct svc_export *exp, > > if ((acc & NFSD_MAY_TRUNC) && IS_APPEND(inode)) > > return nfserr_perm; > > > > + /* > > + * For the purpose of permission checking of NLM requests, > > + * the locker must have READ access or own the file > > + */ > > + if (acc & NFSD_MAY_NLM) > > + acc = NFSD_MAY_READ | NFSD_MAY_OWNER_OVERRIDE; > > + > > I don't agree with this change. > The only time that NFSD_MAY_NLM is set, NFSD_MAY_OWNER_OVERRIDE is also > set. So that part of the change adds no value. > > This change only affects the case where a write lock is being requested. > In that case acc will contains NFSD_MAY_WRITE but not NFSD_MAY_READ. > This change will set NFSD_MAY_READ. Is that really needed? > > Can you please describe the particular problem you saw that is fixed by > this patch? If there is a problem and we do need to add NFSD_MAY_READ, > then I would rather it were done in nlm_fopen(). set export policy with (sec=krb5:...) then mount with sec=krb5,vers=3, then ask for an exclusive flock(), it would fail. The reason it fails is because nlm_fopen() translates lock to open with WRITE. Prior to patch 4cc9b9f2bf4d, the access would be set to acc = NFSD_MAY_READ | NFSD_MAY_OWNER_OVERRIDE; before calling into inode_permission(). The patch changed it and lead to lock no longer being given out with sec=krb5 policy. > > Thanks, > NeilBrown > > > > /* > > * The file owner always gets access permission for accesses that > > * would normally be checked at open time. This is to make > > -- > > 2.47.1 > > > > >
On Fri, 28 Mar 2025, Olga Kornievskaia wrote: > On Thu, Mar 27, 2025 at 7:54 PM NeilBrown <neilb@suse.de> wrote: > > > > On Sat, 22 Mar 2025, Olga Kornievskaia wrote: > > > NLM locking calls need to pass thru file permission checking > > > and for that prior to calling inode_permission() we need > > > to set appropriate access mask. > > > > > > Fixes: 4cc9b9f2bf4d ("nfsd: refine and rename NFSD_MAY_LOCK") > > > Signed-off-by: Olga Kornievskaia <okorniev@redhat.com> > > > --- > > > fs/nfsd/vfs.c | 7 +++++++ > > > 1 file changed, 7 insertions(+) > > > > > > diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c > > > index 4021b047eb18..7928ae21509f 100644 > > > --- a/fs/nfsd/vfs.c > > > +++ b/fs/nfsd/vfs.c > > > @@ -2582,6 +2582,13 @@ nfsd_permission(struct svc_cred *cred, struct svc_export *exp, > > > if ((acc & NFSD_MAY_TRUNC) && IS_APPEND(inode)) > > > return nfserr_perm; > > > > > > + /* > > > + * For the purpose of permission checking of NLM requests, > > > + * the locker must have READ access or own the file > > > + */ > > > + if (acc & NFSD_MAY_NLM) > > > + acc = NFSD_MAY_READ | NFSD_MAY_OWNER_OVERRIDE; > > > + > > > > I don't agree with this change. > > The only time that NFSD_MAY_NLM is set, NFSD_MAY_OWNER_OVERRIDE is also > > set. So that part of the change adds no value. > > > > This change only affects the case where a write lock is being requested. > > In that case acc will contains NFSD_MAY_WRITE but not NFSD_MAY_READ. > > This change will set NFSD_MAY_READ. Is that really needed? > > > > Can you please describe the particular problem you saw that is fixed by > > this patch? If there is a problem and we do need to add NFSD_MAY_READ, > > then I would rather it were done in nlm_fopen(). > > set export policy with (sec=krb5:...) then mount with sec=krb5,vers=3, > then ask for an exclusive flock(), it would fail. > > The reason it fails is because nlm_fopen() translates lock to open > with WRITE. Prior to patch 4cc9b9f2bf4d, the access would be set to > acc = NFSD_MAY_READ | NFSD_MAY_OWNER_OVERRIDE; before calling into > inode_permission(). The patch changed it and lead to lock no longer > being given out with sec=krb5 policy. And do you have WRITE access to the file? check_fmode_for_setlk() in fs/locks.c suggests that for F_WRLCK to be granted the file must be open for FMODE_WRITE. So when an exclusive lock request arrives via NLM, nlm_lookup_file() calls nlm_do_fopen() with a mode of O_WRONLY and that causes nfsd_permission() to check that the caller has write access to the file. So if you are trying to get an exclusive lock to a file that you don't have write access to, then it should fail. If, however, you do have write access to the file - I cannot see why asking for NFSD_MAY_READ instead of NFSD_MAY_WRITE would help. NeilBrown > > > > > > Thanks, > > NeilBrown > > > > > > > /* > > > * The file owner always gets access permission for accesses that > > > * would normally be checked at open time. This is to make > > > -- > > > 2.47.1 > > > > > > > > > >
On 3/27/25 9:43 PM, NeilBrown wrote: > On Fri, 28 Mar 2025, Olga Kornievskaia wrote: >> On Thu, Mar 27, 2025 at 7:54 PM NeilBrown <neilb@suse.de> wrote: >>> >>> On Sat, 22 Mar 2025, Olga Kornievskaia wrote: >>>> NLM locking calls need to pass thru file permission checking >>>> and for that prior to calling inode_permission() we need >>>> to set appropriate access mask. >>>> >>>> Fixes: 4cc9b9f2bf4d ("nfsd: refine and rename NFSD_MAY_LOCK") >>>> Signed-off-by: Olga Kornievskaia <okorniev@redhat.com> >>>> --- >>>> fs/nfsd/vfs.c | 7 +++++++ >>>> 1 file changed, 7 insertions(+) >>>> >>>> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c >>>> index 4021b047eb18..7928ae21509f 100644 >>>> --- a/fs/nfsd/vfs.c >>>> +++ b/fs/nfsd/vfs.c >>>> @@ -2582,6 +2582,13 @@ nfsd_permission(struct svc_cred *cred, struct svc_export *exp, >>>> if ((acc & NFSD_MAY_TRUNC) && IS_APPEND(inode)) >>>> return nfserr_perm; >>>> >>>> + /* >>>> + * For the purpose of permission checking of NLM requests, >>>> + * the locker must have READ access or own the file >>>> + */ >>>> + if (acc & NFSD_MAY_NLM) >>>> + acc = NFSD_MAY_READ | NFSD_MAY_OWNER_OVERRIDE; >>>> + >>> >>> I don't agree with this change. >>> The only time that NFSD_MAY_NLM is set, NFSD_MAY_OWNER_OVERRIDE is also >>> set. So that part of the change adds no value. >>> >>> This change only affects the case where a write lock is being requested. >>> In that case acc will contains NFSD_MAY_WRITE but not NFSD_MAY_READ. >>> This change will set NFSD_MAY_READ. Is that really needed? >>> >>> Can you please describe the particular problem you saw that is fixed by >>> this patch? If there is a problem and we do need to add NFSD_MAY_READ, >>> then I would rather it were done in nlm_fopen(). >> >> set export policy with (sec=krb5:...) then mount with sec=krb5,vers=3, >> then ask for an exclusive flock(), it would fail. >> >> The reason it fails is because nlm_fopen() translates lock to open >> with WRITE. Prior to patch 4cc9b9f2bf4d, the access would be set to >> acc = NFSD_MAY_READ | NFSD_MAY_OWNER_OVERRIDE; before calling into >> inode_permission(). The patch changed it and lead to lock no longer >> being given out with sec=krb5 policy. > > And do you have WRITE access to the file? > > check_fmode_for_setlk() in fs/locks.c suggests that for F_WRLCK to be > granted the file must be open for FMODE_WRITE. > So when an exclusive lock request arrives via NLM, nlm_lookup_file() > calls nlm_do_fopen() with a mode of O_WRONLY and that causes > nfsd_permission() to check that the caller has write access to the file. > > So if you are trying to get an exclusive lock to a file that you don't > have write access to, then it should fail. > If, however, you do have write access to the file - I cannot see why > asking for NFSD_MAY_READ instead of NFSD_MAY_WRITE would help. A little context: 3/3 partially reverts 4cc9b9f2bf4d. Setting exactly READ / OVERRIDE for NLM requests is what nfsd_permission() had done for many years before 4cc9b9f2bf4d. Thus I regard this as a safe thing to do at the moment. I agree, however, that it is mysterious why that should work at all, and I'm fine with holding off on 3/3 until we have a clearer RCA. Initially I thought changing nlm_fopen() would be a better approach, but I think there are other consumers of the MAY flags set by nlm_fopen() that could be impacted by such a change. > NeilBrown > > >> >> >>> >>> Thanks, >>> NeilBrown >>> >>> >>>> /* >>>> * The file owner always gets access permission for accesses that >>>> * would normally be checked at open time. This is to make >>>> -- >>>> 2.47.1 >>>> >>>> >>> >> >> >
On Thu, Mar 27, 2025 at 9:43 PM NeilBrown <neilb@suse.de> wrote: > > On Fri, 28 Mar 2025, Olga Kornievskaia wrote: > > On Thu, Mar 27, 2025 at 7:54 PM NeilBrown <neilb@suse.de> wrote: > > > > > > On Sat, 22 Mar 2025, Olga Kornievskaia wrote: > > > > NLM locking calls need to pass thru file permission checking > > > > and for that prior to calling inode_permission() we need > > > > to set appropriate access mask. > > > > > > > > Fixes: 4cc9b9f2bf4d ("nfsd: refine and rename NFSD_MAY_LOCK") > > > > Signed-off-by: Olga Kornievskaia <okorniev@redhat.com> > > > > --- > > > > fs/nfsd/vfs.c | 7 +++++++ > > > > 1 file changed, 7 insertions(+) > > > > > > > > diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c > > > > index 4021b047eb18..7928ae21509f 100644 > > > > --- a/fs/nfsd/vfs.c > > > > +++ b/fs/nfsd/vfs.c > > > > @@ -2582,6 +2582,13 @@ nfsd_permission(struct svc_cred *cred, struct svc_export *exp, > > > > if ((acc & NFSD_MAY_TRUNC) && IS_APPEND(inode)) > > > > return nfserr_perm; > > > > > > > > + /* > > > > + * For the purpose of permission checking of NLM requests, > > > > + * the locker must have READ access or own the file > > > > + */ > > > > + if (acc & NFSD_MAY_NLM) > > > > + acc = NFSD_MAY_READ | NFSD_MAY_OWNER_OVERRIDE; > > > > + > > > > > > I don't agree with this change. > > > The only time that NFSD_MAY_NLM is set, NFSD_MAY_OWNER_OVERRIDE is also > > > set. So that part of the change adds no value. > > > > > > This change only affects the case where a write lock is being requested. > > > In that case acc will contains NFSD_MAY_WRITE but not NFSD_MAY_READ. > > > This change will set NFSD_MAY_READ. Is that really needed? > > > > > > Can you please describe the particular problem you saw that is fixed by > > > this patch? If there is a problem and we do need to add NFSD_MAY_READ, > > > then I would rather it were done in nlm_fopen(). > > > > set export policy with (sec=krb5:...) then mount with sec=krb5,vers=3, > > then ask for an exclusive flock(), it would fail. > > > > The reason it fails is because nlm_fopen() translates lock to open > > with WRITE. Prior to patch 4cc9b9f2bf4d, the access would be set to > > acc = NFSD_MAY_READ | NFSD_MAY_OWNER_OVERRIDE; before calling into > > inode_permission(). The patch changed it and lead to lock no longer > > being given out with sec=krb5 policy. > > And do you have WRITE access to the file? > > check_fmode_for_setlk() in fs/locks.c suggests that for F_WRLCK to be > granted the file must be open for FMODE_WRITE. > So when an exclusive lock request arrives via NLM, nlm_lookup_file() > calls nlm_do_fopen() with a mode of O_WRONLY and that causes > nfsd_permission() to check that the caller has write access to the file. > > So if you are trying to get an exclusive lock to a file that you don't > have write access to, then it should fail. > If, however, you do have write access to the file - I cannot see why > asking for NFSD_MAY_READ instead of NFSD_MAY_WRITE would help. That's correct, the user doing flock() does NOT have write access to the file. Yet prior to the 4cc9b9f2bf4d, that access was allowed. If that was a bug then my bad. I assumed it was regression. It's interesting to me that on an XFS file system, I can create a file owned by root (on a local filesystem) and then request an exclusive lock on it (as a user -- no write permissions). okorniev@linux:~$ ls -l /export/foobar -rw-r--r--. 1 root root 4 Mar 28 10:46 /export/foobar okorniev@linux:~$ flock -x /export/foobar sleep 1s > > NeilBrown > > > > > > > > > > > > Thanks, > > > NeilBrown > > > > > > > > > > /* > > > > * The file owner always gets access permission for accesses that > > > > * would normally be checked at open time. This is to make > > > > -- > > > > 2.47.1 > > > > > > > > > > > > > > > > >
On Sat, 29 Mar 2025, Olga Kornievskaia wrote: > On Thu, Mar 27, 2025 at 9:43 PM NeilBrown <neilb@suse.de> wrote: > > > > On Fri, 28 Mar 2025, Olga Kornievskaia wrote: > > > On Thu, Mar 27, 2025 at 7:54 PM NeilBrown <neilb@suse.de> wrote: > > > > > > > > On Sat, 22 Mar 2025, Olga Kornievskaia wrote: > > > > > NLM locking calls need to pass thru file permission checking > > > > > and for that prior to calling inode_permission() we need > > > > > to set appropriate access mask. > > > > > > > > > > Fixes: 4cc9b9f2bf4d ("nfsd: refine and rename NFSD_MAY_LOCK") > > > > > Signed-off-by: Olga Kornievskaia <okorniev@redhat.com> > > > > > --- > > > > > fs/nfsd/vfs.c | 7 +++++++ > > > > > 1 file changed, 7 insertions(+) > > > > > > > > > > diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c > > > > > index 4021b047eb18..7928ae21509f 100644 > > > > > --- a/fs/nfsd/vfs.c > > > > > +++ b/fs/nfsd/vfs.c > > > > > @@ -2582,6 +2582,13 @@ nfsd_permission(struct svc_cred *cred, struct svc_export *exp, > > > > > if ((acc & NFSD_MAY_TRUNC) && IS_APPEND(inode)) > > > > > return nfserr_perm; > > > > > > > > > > + /* > > > > > + * For the purpose of permission checking of NLM requests, > > > > > + * the locker must have READ access or own the file > > > > > + */ > > > > > + if (acc & NFSD_MAY_NLM) > > > > > + acc = NFSD_MAY_READ | NFSD_MAY_OWNER_OVERRIDE; > > > > > + > > > > > > > > I don't agree with this change. > > > > The only time that NFSD_MAY_NLM is set, NFSD_MAY_OWNER_OVERRIDE is also > > > > set. So that part of the change adds no value. > > > > > > > > This change only affects the case where a write lock is being requested. > > > > In that case acc will contains NFSD_MAY_WRITE but not NFSD_MAY_READ. > > > > This change will set NFSD_MAY_READ. Is that really needed? > > > > > > > > Can you please describe the particular problem you saw that is fixed by > > > > this patch? If there is a problem and we do need to add NFSD_MAY_READ, > > > > then I would rather it were done in nlm_fopen(). > > > > > > set export policy with (sec=krb5:...) then mount with sec=krb5,vers=3, > > > then ask for an exclusive flock(), it would fail. > > > > > > The reason it fails is because nlm_fopen() translates lock to open > > > with WRITE. Prior to patch 4cc9b9f2bf4d, the access would be set to > > > acc = NFSD_MAY_READ | NFSD_MAY_OWNER_OVERRIDE; before calling into > > > inode_permission(). The patch changed it and lead to lock no longer > > > being given out with sec=krb5 policy. > > > > And do you have WRITE access to the file? > > > > check_fmode_for_setlk() in fs/locks.c suggests that for F_WRLCK to be > > granted the file must be open for FMODE_WRITE. > > So when an exclusive lock request arrives via NLM, nlm_lookup_file() > > calls nlm_do_fopen() with a mode of O_WRONLY and that causes > > nfsd_permission() to check that the caller has write access to the file. > > > > So if you are trying to get an exclusive lock to a file that you don't > > have write access to, then it should fail. > > If, however, you do have write access to the file - I cannot see why > > asking for NFSD_MAY_READ instead of NFSD_MAY_WRITE would help. > > That's correct, the user doing flock() does NOT have write access to > the file. Yet prior to the 4cc9b9f2bf4d, that access was allowed. If > that was a bug then my bad. I assumed it was regression. > > It's interesting to me that on an XFS file system, I can create a file > owned by root (on a local filesystem) and then request an exclusive > lock on it (as a user -- no write permissions). "flock" is the missing piece. I always thought it was a little odd implementing flock locks over NFS using byte-range locking. Not necessarily wrong, but definitely odd. The man page for fcntl says In order to place a read lock, fd must be open for reading. In order to place a write lock, fd must be open for writing. To place both types of lock, open a file read-write. So byte-range locks require a consistent open mode. The man page for flock says A shared or exclusive lock can be placed on a file regardless of the mode in which the file was opened. Since the NFS client started using NLM (or v4 LOCK) for flock requests, we cannot know if a request is flock or fcntl so we cannot check the "correct" permissions. We have to rely on the client doing the permission checking. So it isn't really correct to check for either READ or WRITE. This is awkward because nfsd doesn't just check permissions. It has to open the file and say what mode it is opening for. This is apparently important when re-exporting NFS according to Commit: 7f024fcd5c97 ("Keep read and write fds with each nlm_file") So if you try an exclusive flock on a re-exported NFS file (reexported over v3) that you have open for READ but do not have write permission for, then the client will allow it, but the intermediate server will try a O_WRITE open which the final server will reject. (does re-export work over v3??) There is no way to make this "work". As I said: sending flock requests over NFS was an interesting choice. For v4 re-export it isn't a problem because the intermediate server knows what mode the file was opened for on the client. So what do we do? Whatever we do needs a comment explaining that flock vs fcntl is the problem. Possibly we should not require read or write access - and just trust the client. Alternately we could stick with the current practice of requiring READ but not WRITE - it would be rare to lock a file which you don't have read access to. So yes: we do need a patch here. I would suggest something like: /* An NLM request may be from fcntl() which requires the open mode to * match to lock mode or may be from flock() which allows any lock mode * with any open mode. "acc" here indicates the lock mode but we must * do permission check reflecting the open mode which we cannot know. * For simplicity and historical continuity, always only check for * READ access */ if (acc & NFSD_MAY_NLM) acc = (acc & ~NFSD_MAY_WRITE) | NFSD_MAY_READ; I'd prefer to leave the MAY_OWNER_OVERRIDE setting in nlm_fopen(). Thanks, NeilBrown
On 3/28/2025 5:53 PM, NeilBrown wrote: > On Sat, 29 Mar 2025, Olga Kornievskaia wrote: >> On Thu, Mar 27, 2025 at 9:43 PM NeilBrown <neilb@suse.de> wrote: >>> >>> On Fri, 28 Mar 2025, Olga Kornievskaia wrote: >>>> On Thu, Mar 27, 2025 at 7:54 PM NeilBrown <neilb@suse.de> wrote: >>>>> >>>>> On Sat, 22 Mar 2025, Olga Kornievskaia wrote: >>>>>> NLM locking calls need to pass thru file permission checking >>>>>> and for that prior to calling inode_permission() we need >>>>>> to set appropriate access mask. >>>>>> >>>>>> Fixes: 4cc9b9f2bf4d ("nfsd: refine and rename NFSD_MAY_LOCK") >>>>>> Signed-off-by: Olga Kornievskaia <okorniev@redhat.com> >>>>>> --- >>>>>> fs/nfsd/vfs.c | 7 +++++++ >>>>>> 1 file changed, 7 insertions(+) >>>>>> >>>>>> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c >>>>>> index 4021b047eb18..7928ae21509f 100644 >>>>>> --- a/fs/nfsd/vfs.c >>>>>> +++ b/fs/nfsd/vfs.c >>>>>> @@ -2582,6 +2582,13 @@ nfsd_permission(struct svc_cred *cred, struct svc_export *exp, >>>>>> if ((acc & NFSD_MAY_TRUNC) && IS_APPEND(inode)) >>>>>> return nfserr_perm; >>>>>> >>>>>> + /* >>>>>> + * For the purpose of permission checking of NLM requests, >>>>>> + * the locker must have READ access or own the file >>>>>> + */ >>>>>> + if (acc & NFSD_MAY_NLM) >>>>>> + acc = NFSD_MAY_READ | NFSD_MAY_OWNER_OVERRIDE; >>>>>> + >>>>> >>>>> I don't agree with this change. >>>>> The only time that NFSD_MAY_NLM is set, NFSD_MAY_OWNER_OVERRIDE is also >>>>> set. So that part of the change adds no value. >>>>> >>>>> This change only affects the case where a write lock is being requested. >>>>> In that case acc will contains NFSD_MAY_WRITE but not NFSD_MAY_READ. >>>>> This change will set NFSD_MAY_READ. Is that really needed? >>>>> >>>>> Can you please describe the particular problem you saw that is fixed by >>>>> this patch? If there is a problem and we do need to add NFSD_MAY_READ, >>>>> then I would rather it were done in nlm_fopen(). >>>> >>>> set export policy with (sec=krb5:...) then mount with sec=krb5,vers=3, >>>> then ask for an exclusive flock(), it would fail. >>>> >>>> The reason it fails is because nlm_fopen() translates lock to open >>>> with WRITE. Prior to patch 4cc9b9f2bf4d, the access would be set to >>>> acc = NFSD_MAY_READ | NFSD_MAY_OWNER_OVERRIDE; before calling into >>>> inode_permission(). The patch changed it and lead to lock no longer >>>> being given out with sec=krb5 policy. >>> >>> And do you have WRITE access to the file? >>> >>> check_fmode_for_setlk() in fs/locks.c suggests that for F_WRLCK to be >>> granted the file must be open for FMODE_WRITE. >>> So when an exclusive lock request arrives via NLM, nlm_lookup_file() >>> calls nlm_do_fopen() with a mode of O_WRONLY and that causes >>> nfsd_permission() to check that the caller has write access to the file. >>> >>> So if you are trying to get an exclusive lock to a file that you don't >>> have write access to, then it should fail. >>> If, however, you do have write access to the file - I cannot see why >>> asking for NFSD_MAY_READ instead of NFSD_MAY_WRITE would help. >> >> That's correct, the user doing flock() does NOT have write access to >> the file. Yet prior to the 4cc9b9f2bf4d, that access was allowed. If >> that was a bug then my bad. I assumed it was regression. >> >> It's interesting to me that on an XFS file system, I can create a file >> owned by root (on a local filesystem) and then request an exclusive >> lock on it (as a user -- no write permissions). > > "flock" is the missing piece. I always thought it was a little odd > implementing flock locks over NFS using byte-range locking. Not > necessarily wrong, but definitely odd. > > The man page for fcntl says > > In order to place a read lock, fd must be open for reading. In order > to place a write lock, fd must be open for writing. To place both > types of lock, open a file read-write. > > So byte-range locks require a consistent open mode. > > The man page for flock says > > A shared or exclusive lock can be placed on a file regardless of the > mode in which the file was opened. > > Since the NFS client started using NLM (or v4 LOCK) for flock requests, > we cannot know if a request is flock or fcntl so we cannot check the > "correct" permissions. We have to rely on the client doing the > permission checking. > > So it isn't really correct to check for either READ or WRITE. Just one thing to mention, newer versions of the flock(2) manpage do mention the NFS/NLM behavior w.r.t. open for writing: Since Linux 2.6.12, NFS clients support flock() locks by emulating them as fcntl(2) byte-range locks on the entire file. This means that fcntl(2) and flock() locks do interact with one another over NFS. It also means that in order to place an exclusive lock, the file must be opened for writing. Not sure this solves the question, but it's "documented". The text should maybe be revisited either way. Tom. > This is awkward because nfsd doesn't just check permissions. It has to > open the file and say what mode it is opening for. This is apparently > important when re-exporting NFS according to > > Commit: 7f024fcd5c97 ("Keep read and write fds with each nlm_file") > > So if you try an exclusive flock on a re-exported NFS file (reexported > over v3) that you have open for READ but do not have write permission > for, then the client will allow it, but the intermediate server will try > a O_WRITE open which the final server will reject. > (does re-export work over v3??) > > There is no way to make this "work". As I said: sending flock requests > over NFS was an interesting choice. > For v4 re-export it isn't a problem because the intermediate server > knows what mode the file was opened for on the client. > > So what do we do? Whatever we do needs a comment explaining that flock > vs fcntl is the problem. > Possibly we should not require read or write access - and just trust the > client. Alternately we could stick with the current practice of > requiring READ but not WRITE - it would be rare to lock a file which you > don't have read access to. > > So yes: we do need a patch here. I would suggest something like: > > /* An NLM request may be from fcntl() which requires the open mode to > * match to lock mode or may be from flock() which allows any lock mode > * with any open mode. "acc" here indicates the lock mode but we must > * do permission check reflecting the open mode which we cannot know. > * For simplicity and historical continuity, always only check for > * READ access > */ > if (acc & NFSD_MAY_NLM) > acc = (acc & ~NFSD_MAY_WRITE) | NFSD_MAY_READ; > > I'd prefer to leave the MAY_OWNER_OVERRIDE setting in nlm_fopen(). > > Thanks, > NeilBrown >
On Fri, Mar 28, 2025 at 5:53 PM NeilBrown <neilb@suse.de> wrote: > > On Sat, 29 Mar 2025, Olga Kornievskaia wrote: > > On Thu, Mar 27, 2025 at 9:43 PM NeilBrown <neilb@suse.de> wrote: > > > > > > On Fri, 28 Mar 2025, Olga Kornievskaia wrote: > > > > On Thu, Mar 27, 2025 at 7:54 PM NeilBrown <neilb@suse.de> wrote: > > > > > > > > > > On Sat, 22 Mar 2025, Olga Kornievskaia wrote: > > > > > > NLM locking calls need to pass thru file permission checking > > > > > > and for that prior to calling inode_permission() we need > > > > > > to set appropriate access mask. > > > > > > > > > > > > Fixes: 4cc9b9f2bf4d ("nfsd: refine and rename NFSD_MAY_LOCK") > > > > > > Signed-off-by: Olga Kornievskaia <okorniev@redhat.com> > > > > > > --- > > > > > > fs/nfsd/vfs.c | 7 +++++++ > > > > > > 1 file changed, 7 insertions(+) > > > > > > > > > > > > diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c > > > > > > index 4021b047eb18..7928ae21509f 100644 > > > > > > --- a/fs/nfsd/vfs.c > > > > > > +++ b/fs/nfsd/vfs.c > > > > > > @@ -2582,6 +2582,13 @@ nfsd_permission(struct svc_cred *cred, struct svc_export *exp, > > > > > > if ((acc & NFSD_MAY_TRUNC) && IS_APPEND(inode)) > > > > > > return nfserr_perm; > > > > > > > > > > > > + /* > > > > > > + * For the purpose of permission checking of NLM requests, > > > > > > + * the locker must have READ access or own the file > > > > > > + */ > > > > > > + if (acc & NFSD_MAY_NLM) > > > > > > + acc = NFSD_MAY_READ | NFSD_MAY_OWNER_OVERRIDE; > > > > > > + > > > > > > > > > > I don't agree with this change. > > > > > The only time that NFSD_MAY_NLM is set, NFSD_MAY_OWNER_OVERRIDE is also > > > > > set. So that part of the change adds no value. > > > > > > > > > > This change only affects the case where a write lock is being requested. > > > > > In that case acc will contains NFSD_MAY_WRITE but not NFSD_MAY_READ. > > > > > This change will set NFSD_MAY_READ. Is that really needed? > > > > > > > > > > Can you please describe the particular problem you saw that is fixed by > > > > > this patch? If there is a problem and we do need to add NFSD_MAY_READ, > > > > > then I would rather it were done in nlm_fopen(). > > > > > > > > set export policy with (sec=krb5:...) then mount with sec=krb5,vers=3, > > > > then ask for an exclusive flock(), it would fail. > > > > > > > > The reason it fails is because nlm_fopen() translates lock to open > > > > with WRITE. Prior to patch 4cc9b9f2bf4d, the access would be set to > > > > acc = NFSD_MAY_READ | NFSD_MAY_OWNER_OVERRIDE; before calling into > > > > inode_permission(). The patch changed it and lead to lock no longer > > > > being given out with sec=krb5 policy. > > > > > > And do you have WRITE access to the file? > > > > > > check_fmode_for_setlk() in fs/locks.c suggests that for F_WRLCK to be > > > granted the file must be open for FMODE_WRITE. > > > So when an exclusive lock request arrives via NLM, nlm_lookup_file() > > > calls nlm_do_fopen() with a mode of O_WRONLY and that causes > > > nfsd_permission() to check that the caller has write access to the file. > > > > > > So if you are trying to get an exclusive lock to a file that you don't > > > have write access to, then it should fail. > > > If, however, you do have write access to the file - I cannot see why > > > asking for NFSD_MAY_READ instead of NFSD_MAY_WRITE would help. > > > > That's correct, the user doing flock() does NOT have write access to > > the file. Yet prior to the 4cc9b9f2bf4d, that access was allowed. If > > that was a bug then my bad. I assumed it was regression. > > > > It's interesting to me that on an XFS file system, I can create a file > > owned by root (on a local filesystem) and then request an exclusive > > lock on it (as a user -- no write permissions). > > "flock" is the missing piece. I always thought it was a little odd > implementing flock locks over NFS using byte-range locking. Not > necessarily wrong, but definitely odd. > > The man page for fcntl says > > In order to place a read lock, fd must be open for reading. In order > to place a write lock, fd must be open for writing. To place both > types of lock, open a file read-write. > > So byte-range locks require a consistent open mode. > > The man page for flock says > > A shared or exclusive lock can be placed on a file regardless of the > mode in which the file was opened. > > Since the NFS client started using NLM (or v4 LOCK) for flock requests, > we cannot know if a request is flock or fcntl so we cannot check the > "correct" permissions. We have to rely on the client doing the > permission checking. > > So it isn't really correct to check for either READ or WRITE. > > This is awkward because nfsd doesn't just check permissions. It has to > open the file and say what mode it is opening for. This is apparently > important when re-exporting NFS according to > > Commit: 7f024fcd5c97 ("Keep read and write fds with each nlm_file") > > So if you try an exclusive flock on a re-exported NFS file (reexported > over v3) that you have open for READ but do not have write permission > for, then the client will allow it, but the intermediate server will try > a O_WRITE open which the final server will reject. > (does re-export work over v3??) > > There is no way to make this "work". As I said: sending flock requests > over NFS was an interesting choice. > For v4 re-export it isn't a problem because the intermediate server > knows what mode the file was opened for on the client. > > So what do we do? Whatever we do needs a comment explaining that flock > vs fcntl is the problem. > Possibly we should not require read or write access - and just trust the > client. Alternately we could stick with the current practice of > requiring READ but not WRITE - it would be rare to lock a file which you > don't have read access to. > > So yes: we do need a patch here. I would suggest something like: > > /* An NLM request may be from fcntl() which requires the open mode to > * match to lock mode or may be from flock() which allows any lock mode > * with any open mode. "acc" here indicates the lock mode but we must > * do permission check reflecting the open mode which we cannot know. > * For simplicity and historical continuity, always only check for > * READ access > */ > if (acc & NFSD_MAY_NLM) > acc = (acc & ~NFSD_MAY_WRITE) | NFSD_MAY_READ; This code would also make the behaviour consistent with prior to 4cc9b9f2bf4d. But now I question whether or not the new behaviour is what is desired going forward or not? Here's another thing to consider: the same command done over nfsv4 returns an error. I guess nobody ever complained that flock over v3 was successful but failed over v4? > I'd prefer to leave the MAY_OWNER_OVERRIDE setting in nlm_fopen(). > > Thanks, > NeilBrown
On 3/28/25 7:29 PM, Tom Talpey wrote: > On 3/28/2025 5:53 PM, NeilBrown wrote: >> On Sat, 29 Mar 2025, Olga Kornievskaia wrote: >>> On Thu, Mar 27, 2025 at 9:43 PM NeilBrown <neilb@suse.de> wrote: >>>> >>>> On Fri, 28 Mar 2025, Olga Kornievskaia wrote: >>>>> On Thu, Mar 27, 2025 at 7:54 PM NeilBrown <neilb@suse.de> wrote: >>>>>> >>>>>> On Sat, 22 Mar 2025, Olga Kornievskaia wrote: >>>>>>> NLM locking calls need to pass thru file permission checking >>>>>>> and for that prior to calling inode_permission() we need >>>>>>> to set appropriate access mask. >>>>>>> >>>>>>> Fixes: 4cc9b9f2bf4d ("nfsd: refine and rename NFSD_MAY_LOCK") >>>>>>> Signed-off-by: Olga Kornievskaia <okorniev@redhat.com> >>>>>>> --- >>>>>>> fs/nfsd/vfs.c | 7 +++++++ >>>>>>> 1 file changed, 7 insertions(+) >>>>>>> >>>>>>> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c >>>>>>> index 4021b047eb18..7928ae21509f 100644 >>>>>>> --- a/fs/nfsd/vfs.c >>>>>>> +++ b/fs/nfsd/vfs.c >>>>>>> @@ -2582,6 +2582,13 @@ nfsd_permission(struct svc_cred *cred, >>>>>>> struct svc_export *exp, >>>>>>> if ((acc & NFSD_MAY_TRUNC) && IS_APPEND(inode)) >>>>>>> return nfserr_perm; >>>>>>> >>>>>>> + /* >>>>>>> + * For the purpose of permission checking of NLM requests, >>>>>>> + * the locker must have READ access or own the file >>>>>>> + */ >>>>>>> + if (acc & NFSD_MAY_NLM) >>>>>>> + acc = NFSD_MAY_READ | NFSD_MAY_OWNER_OVERRIDE; >>>>>>> + >>>>>> >>>>>> I don't agree with this change. >>>>>> The only time that NFSD_MAY_NLM is set, NFSD_MAY_OWNER_OVERRIDE is >>>>>> also >>>>>> set. So that part of the change adds no value. >>>>>> >>>>>> This change only affects the case where a write lock is being >>>>>> requested. >>>>>> In that case acc will contains NFSD_MAY_WRITE but not NFSD_MAY_READ. >>>>>> This change will set NFSD_MAY_READ. Is that really needed? >>>>>> >>>>>> Can you please describe the particular problem you saw that is >>>>>> fixed by >>>>>> this patch? If there is a problem and we do need to add >>>>>> NFSD_MAY_READ, >>>>>> then I would rather it were done in nlm_fopen(). >>>>> >>>>> set export policy with (sec=krb5:...) then mount with sec=krb5,vers=3, >>>>> then ask for an exclusive flock(), it would fail. >>>>> >>>>> The reason it fails is because nlm_fopen() translates lock to open >>>>> with WRITE. Prior to patch 4cc9b9f2bf4d, the access would be set to >>>>> acc = NFSD_MAY_READ | NFSD_MAY_OWNER_OVERRIDE; before calling into >>>>> inode_permission(). The patch changed it and lead to lock no longer >>>>> being given out with sec=krb5 policy. >>>> >>>> And do you have WRITE access to the file? >>>> >>>> check_fmode_for_setlk() in fs/locks.c suggests that for F_WRLCK to be >>>> granted the file must be open for FMODE_WRITE. >>>> So when an exclusive lock request arrives via NLM, nlm_lookup_file() >>>> calls nlm_do_fopen() with a mode of O_WRONLY and that causes >>>> nfsd_permission() to check that the caller has write access to the >>>> file. >>>> >>>> So if you are trying to get an exclusive lock to a file that you don't >>>> have write access to, then it should fail. >>>> If, however, you do have write access to the file - I cannot see why >>>> asking for NFSD_MAY_READ instead of NFSD_MAY_WRITE would help. >>> >>> That's correct, the user doing flock() does NOT have write access to >>> the file. Yet prior to the 4cc9b9f2bf4d, that access was allowed. If >>> that was a bug then my bad. I assumed it was regression. >>> >>> It's interesting to me that on an XFS file system, I can create a file >>> owned by root (on a local filesystem) and then request an exclusive >>> lock on it (as a user -- no write permissions). >> >> "flock" is the missing piece. I always thought it was a little odd >> implementing flock locks over NFS using byte-range locking. Not >> necessarily wrong, but definitely odd. >> >> The man page for fcntl says >> >> In order to place a read lock, fd must be open for reading. In order >> to place a write lock, fd must be open for writing. To place both >> types of lock, open a file read-write. >> >> So byte-range locks require a consistent open mode. >> >> The man page for flock says >> >> A shared or exclusive lock can be placed on a file regardless of the >> mode in which the file was opened. >> >> Since the NFS client started using NLM (or v4 LOCK) for flock requests, >> we cannot know if a request is flock or fcntl so we cannot check the >> "correct" permissions. We have to rely on the client doing the >> permission checking. >> >> So it isn't really correct to check for either READ or WRITE. > > Just one thing to mention, newer versions of the flock(2) manpage do > mention the NFS/NLM behavior w.r.t. open for writing: > > Since Linux 2.6.12, NFS clients support flock() locks by emulating > them as fcntl(2) byte-range locks on the entire file. This means > that fcntl(2) and flock() locks do interact with one another over > NFS. It also means that in order to place an exclusive lock, the > file must be opened for writing. > > Not sure this solves the question, but it's "documented". The text > should maybe be revisited either way. Thanks, Neil and Tom, for digging this out. I agree that the new code comment should explicitly mention that this logic is necessary due to our NFSv3 implementation emulating flock() with fcntl() byte-range locks. > Tom. > >> This is awkward because nfsd doesn't just check permissions. It has to >> open the file and say what mode it is opening for. This is apparently >> important when re-exporting NFS according to >> >> Commit: 7f024fcd5c97 ("Keep read and write fds with each nlm_file") >> >> So if you try an exclusive flock on a re-exported NFS file (reexported >> over v3) that you have open for READ but do not have write permission >> for, then the client will allow it, but the intermediate server will try >> a O_WRITE open which the final server will reject. >> (does re-export work over v3??) >> >> There is no way to make this "work". As I said: sending flock requests >> over NFS was an interesting choice. >> For v4 re-export it isn't a problem because the intermediate server >> knows what mode the file was opened for on the client. >> >> So what do we do? Whatever we do needs a comment explaining that flock >> vs fcntl is the problem. >> Possibly we should not require read or write access - and just trust the >> client. Alternately we could stick with the current practice of >> requiring READ but not WRITE - it would be rare to lock a file which you >> don't have read access to. >> >> So yes: we do need a patch here. I would suggest something like: >> >> /* An NLM request may be from fcntl() which requires the open mode to >> * match to lock mode or may be from flock() which allows any lock mode >> * with any open mode. "acc" here indicates the lock mode but we must >> * do permission check reflecting the open mode which we cannot know. >> * For simplicity and historical continuity, always only check for >> * READ access >> */ >> if (acc & NFSD_MAY_NLM) >> acc = (acc & ~NFSD_MAY_WRITE) | NFSD_MAY_READ; >> >> I'd prefer to leave the MAY_OWNER_OVERRIDE setting in nlm_fopen(). >> >> Thanks, >> NeilBrown >> >
On Mon, 31 Mar 2025, Olga Kornievskaia wrote: > > This code would also make the behaviour consistent with prior to > 4cc9b9f2bf4d. But now I question whether or not the new behaviour is > what is desired going forward or not? > > Here's another thing to consider: the same command done over nfsv4 > returns an error. I guess nobody ever complained that flock over v3 > was successful but failed over v4? That is useful. Given that: - exclusive flock without write access over v4 never worked - As Tom notes, new man pages document that exclusive flock without write access isn't expected to work over NFS - it is hard to think of a genuine use case for exclusive flock without write access I'm inclined to leave this code as it is and declare your failing test to no longer be invalid. That is technically a regression, but regressions only matter if people notice them (and complain to Linus). No harm - no fowl. Thanks, NeilBrown
On 3/30/25 8:10 PM, NeilBrown wrote: > On Mon, 31 Mar 2025, Olga Kornievskaia wrote: >> >> This code would also make the behaviour consistent with prior to >> 4cc9b9f2bf4d. But now I question whether or not the new behaviour is >> what is desired going forward or not? >> >> Here's another thing to consider: the same command done over nfsv4 >> returns an error. I guess nobody ever complained that flock over v3 >> was successful but failed over v4? > > That is useful. Given that: > - exclusive flock without write access over v4 never worked > - As Tom notes, new man pages document that exclusive flock without write access > isn't expected to work over NFS > - it is hard to think of a genuine use case for exclusive flock without > write access > > I'm inclined to leave this code as it is and declare your failing test > to no longer be invalid. For the record, which test exactly is failing? Is there a BugLink? > That is technically a regression, but > regressions only matter if people notice them (and complain to Linus). > No harm - no fowl.
On Mon, Mar 31, 2025 at 10:49 AM Chuck Lever <chuck.lever@oracle.com> wrote: > > On 3/30/25 8:10 PM, NeilBrown wrote: > > On Mon, 31 Mar 2025, Olga Kornievskaia wrote: > >> > >> This code would also make the behaviour consistent with prior to > >> 4cc9b9f2bf4d. But now I question whether or not the new behaviour is > >> what is desired going forward or not? > >> > >> Here's another thing to consider: the same command done over nfsv4 > >> returns an error. I guess nobody ever complained that flock over v3 > >> was successful but failed over v4? > > > > That is useful. Given that: > > - exclusive flock without write access over v4 never worked > > - As Tom notes, new man pages document that exclusive flock without write access > > isn't expected to work over NFS > > - it is hard to think of a genuine use case for exclusive flock without > > write access > > > > I'm inclined to leave this code as it is and declare your failing test > > to no longer be invalid. > > For the record, which test exactly is failing? Is there a BugLink? Test is just an flock()? > > > > That is technically a regression, but > > regressions only matter if people notice them (and complain to Linus). > > No harm - no fowl. > > -- > Chuck Lever >
On Tue, 01 Apr 2025, Olga Kornievskaia wrote: > On Mon, Mar 31, 2025 at 10:49 AM Chuck Lever <chuck.lever@oracle.com> wrote: > > > > On 3/30/25 8:10 PM, NeilBrown wrote: > > > On Mon, 31 Mar 2025, Olga Kornievskaia wrote: > > >> > > >> This code would also make the behaviour consistent with prior to > > >> 4cc9b9f2bf4d. But now I question whether or not the new behaviour is > > >> what is desired going forward or not? > > >> > > >> Here's another thing to consider: the same command done over nfsv4 > > >> returns an error. I guess nobody ever complained that flock over v3 > > >> was successful but failed over v4? > > > > > > That is useful. Given that: > > > - exclusive flock without write access over v4 never worked > > > - As Tom notes, new man pages document that exclusive flock without write access > > > isn't expected to work over NFS > > > - it is hard to think of a genuine use case for exclusive flock without > > > write access > > > > > > I'm inclined to leave this code as it is and declare your failing test > > > to no longer be invalid. > > > > For the record, which test exactly is failing? Is there a BugLink? > > Test is just an flock()? > But what motivated you to perform that specific test: exclusive flock over NFSv3 on a file you didn't have write permission to ?? Is it part of a test suite? Or is it done by some application? or .... NeilBrown
On Tue, Apr 1, 2025 at 6:24 PM NeilBrown <neilb@suse.de> wrote: > > On Tue, 01 Apr 2025, Olga Kornievskaia wrote: > > On Mon, Mar 31, 2025 at 10:49 AM Chuck Lever <chuck.lever@oracle.com> wrote: > > > > > > On 3/30/25 8:10 PM, NeilBrown wrote: > > > > On Mon, 31 Mar 2025, Olga Kornievskaia wrote: > > > >> > > > >> This code would also make the behaviour consistent with prior to > > > >> 4cc9b9f2bf4d. But now I question whether or not the new behaviour is > > > >> what is desired going forward or not? > > > >> > > > >> Here's another thing to consider: the same command done over nfsv4 > > > >> returns an error. I guess nobody ever complained that flock over v3 > > > >> was successful but failed over v4? > > > > > > > > That is useful. Given that: > > > > - exclusive flock without write access over v4 never worked > > > > - As Tom notes, new man pages document that exclusive flock without write access > > > > isn't expected to work over NFS > > > > - it is hard to think of a genuine use case for exclusive flock without > > > > write access > > > > > > > > I'm inclined to leave this code as it is and declare your failing test > > > > to no longer be invalid. > > > > > > For the record, which test exactly is failing? Is there a BugLink? > > > > Test is just an flock()? > > > > But what motivated you to perform that specific test: > exclusive flock over NFSv3 on a file you didn't have write permission to > ?? > > Is it part of a test suite? Or is it done by some application? or .... A long story. It started with xfstest failing for sec=tls policy (ie thus the other 2 patches in the series). But I saw that it's just an flock that was failing so I stopped doing xfstest and just using an flock. But as I started digging into the bisected patch I was trying to understand the code and thus started using other export policies. > NeilBrown
On Wed, 02 Apr 2025, Olga Kornievskaia wrote: > On Tue, Apr 1, 2025 at 6:24 PM NeilBrown <neilb@suse.de> wrote: > > > > On Tue, 01 Apr 2025, Olga Kornievskaia wrote: > > > On Mon, Mar 31, 2025 at 10:49 AM Chuck Lever <chuck.lever@oracle.com> wrote: > > > > > > > > On 3/30/25 8:10 PM, NeilBrown wrote: > > > > > On Mon, 31 Mar 2025, Olga Kornievskaia wrote: > > > > >> > > > > >> This code would also make the behaviour consistent with prior to > > > > >> 4cc9b9f2bf4d. But now I question whether or not the new behaviour is > > > > >> what is desired going forward or not? > > > > >> > > > > >> Here's another thing to consider: the same command done over nfsv4 > > > > >> returns an error. I guess nobody ever complained that flock over v3 > > > > >> was successful but failed over v4? > > > > > > > > > > That is useful. Given that: > > > > > - exclusive flock without write access over v4 never worked > > > > > - As Tom notes, new man pages document that exclusive flock without write access > > > > > isn't expected to work over NFS > > > > > - it is hard to think of a genuine use case for exclusive flock without > > > > > write access > > > > > > > > > > I'm inclined to leave this code as it is and declare your failing test > > > > > to no longer be invalid. > > > > > > > > For the record, which test exactly is failing? Is there a BugLink? > > > > > > Test is just an flock()? > > > > > > > But what motivated you to perform that specific test: > > exclusive flock over NFSv3 on a file you didn't have write permission to > > ?? > > > > Is it part of a test suite? Or is it done by some application? or .... > > A long story. It started with xfstest failing for sec=tls policy (ie > thus the other 2 patches in the series). But I saw that it's just an > flock that was failing so I stopped doing xfstest and just using an > flock. But as I started digging into the bisected patch I was trying > to understand the code and thus started using other export policies. That all makes perfect sense - thanks. So the fact that you noticed was primarily based on code inspection and does not suggest that other people might also notice the change and see it as a regression. That strengthens my feeling that the change should be seen as a bug-fix, not as a regression. So we don't need to "fix" it. Thanks, NeilBrown
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c index 4021b047eb18..7928ae21509f 100644 --- a/fs/nfsd/vfs.c +++ b/fs/nfsd/vfs.c @@ -2582,6 +2582,13 @@ nfsd_permission(struct svc_cred *cred, struct svc_export *exp, if ((acc & NFSD_MAY_TRUNC) && IS_APPEND(inode)) return nfserr_perm; + /* + * For the purpose of permission checking of NLM requests, + * the locker must have READ access or own the file + */ + if (acc & NFSD_MAY_NLM) + acc = NFSD_MAY_READ | NFSD_MAY_OWNER_OVERRIDE; + /* * The file owner always gets access permission for accesses that * would normally be checked at open time. This is to make
NLM locking calls need to pass thru file permission checking and for that prior to calling inode_permission() we need to set appropriate access mask. Fixes: 4cc9b9f2bf4d ("nfsd: refine and rename NFSD_MAY_LOCK") Signed-off-by: Olga Kornievskaia <okorniev@redhat.com> --- fs/nfsd/vfs.c | 7 +++++++ 1 file changed, 7 insertions(+)