| Message ID | 20220726202333.165490-1-jlayton@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [RFC] vfs: don't check may_create_in_sticky if the file is already open/created | expand |
On Tue, 2022-07-26 at 16:23 -0400, Jeff Layton wrote: > NFS server is exporting a sticky directory (mode 01777) with root > squashing enabled. Client has protect_regular enabled and then tries to > open a file as root in that directory. File is created (with ownership > set to nobody:nobody) but the open syscall returns an error. > > The problem is may_create_in_sticky, which rejects the open even though > the file has already been created/opened. Only call may_create_in_sticky > if the file hasn't already been opened or created. > > Cc: Christian Brauner <brauner@kernel.org> > Link: https://bugzilla.redhat.com/show_bug.cgi?id=1976829 > Reported-by: Yongchen Yang <yoyang@redhat.com> > Signed-off-by: Jeff Layton <jlayton@kernel.org> > --- > fs/namei.c | 13 +++++++++---- > 1 file changed, 9 insertions(+), 4 deletions(-) > > diff --git a/fs/namei.c b/fs/namei.c > index 1f28d3f463c3..7480b6dc8d27 100644 > --- a/fs/namei.c > +++ b/fs/namei.c > @@ -3495,10 +3495,15 @@ static int do_open(struct nameidata *nd, > return -EEXIST; > if (d_is_dir(nd->path.dentry)) > return -EISDIR; > - error = may_create_in_sticky(mnt_userns, nd, > - d_backing_inode(nd->path.dentry)); > - if (unlikely(error)) > - return error; > + if (!(file->f_mode & (FMODE_OPENED | FMODE_CREATED))) { > + error = may_create_in_sticky(mnt_userns, nd, > + d_backing_inode(nd->path.dentry)); > + if (unlikely(error)) { > + printk("%s: f_mode=0x%x oflag=0x%x\n", > + __func__, file->f_mode, open_flag); > + return error; > + } > + } > } > if ((nd->flags & LOOKUP_DIRECTORY) && !d_can_lookup(nd->path.dentry)) > return -ENOTDIR; I'm pretty sure this patch is the wrong approach, actually, since it doesn't fix the regular (non-atomic) open codepath. Any thoughts on what the right fix might be?
On Tue, Jul 26, 2022 at 04:27:56PM -0400, Jeff Layton wrote: > On Tue, 2022-07-26 at 16:23 -0400, Jeff Layton wrote: > > NFS server is exporting a sticky directory (mode 01777) with root > > squashing enabled. Client has protect_regular enabled and then tries to > > open a file as root in that directory. File is created (with ownership > > set to nobody:nobody) but the open syscall returns an error. > > > > The problem is may_create_in_sticky, which rejects the open even though > > the file has already been created/opened. Only call may_create_in_sticky > > if the file hasn't already been opened or created. > > > > Cc: Christian Brauner <brauner@kernel.org> > > Link: https://bugzilla.redhat.com/show_bug.cgi?id=1976829 > > Reported-by: Yongchen Yang <yoyang@redhat.com> > > Signed-off-by: Jeff Layton <jlayton@kernel.org> > > --- > > fs/namei.c | 13 +++++++++---- > > 1 file changed, 9 insertions(+), 4 deletions(-) > > > > diff --git a/fs/namei.c b/fs/namei.c > > index 1f28d3f463c3..7480b6dc8d27 100644 > > --- a/fs/namei.c > > +++ b/fs/namei.c > > @@ -3495,10 +3495,15 @@ static int do_open(struct nameidata *nd, > > return -EEXIST; > > if (d_is_dir(nd->path.dentry)) > > return -EISDIR; > > - error = may_create_in_sticky(mnt_userns, nd, > > - d_backing_inode(nd->path.dentry)); > > - if (unlikely(error)) > > - return error; > > + if (!(file->f_mode & (FMODE_OPENED | FMODE_CREATED))) { > > + error = may_create_in_sticky(mnt_userns, nd, > > + d_backing_inode(nd->path.dentry)); > > + if (unlikely(error)) { > > + printk("%s: f_mode=0x%x oflag=0x%x\n", > > + __func__, file->f_mode, open_flag); > > + return error; > > + } > > + } > > } > > if ((nd->flags & LOOKUP_DIRECTORY) && !d_can_lookup(nd->path.dentry)) > > return -ENOTDIR; > > I'm pretty sure this patch is the wrong approach, actually, since it > doesn't fix the regular (non-atomic) open codepath. Any thoughts on what Hey Jeff, I haven't quite understood why that won't work for the regular open codepaths. I'm probably missing something obvious. > the right fix might be? When an actual creation has taken place - and not just a lookup - then may_create_in_sticky() assumes that the owner of the inode matches current_fsuid(). That'd would also be problematic on fat or in fact on any fs where the actual inode->i_{g,u}id are based on e.g. uid/gid mount options and not on current_fsuid(), I think? So in order to improve this we would need to work around that assumption in some way. Either by skipping may_create_in_sticky() if the file got created or by adapting may_create_in_sticky(). I only wonder whether skipping may_create_in_sticky() altogether might be a bit too lax. One possibility that came to my mind might be to relax this assumption when the file has been created and the creator has CAP_FOWNER. So (not compile tested or in any way) sm like: diff --git a/fs/namei.c b/fs/namei.c index 1f28d3f463c3..239e9f423346 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -1221,7 +1221,8 @@ int may_linkat(struct user_namespace *mnt_userns, struct path *link) * Returns 0 if the open is allowed, -ve on error. */ static int may_create_in_sticky(struct user_namespace *mnt_userns, - struct nameidata *nd, struct inode *const inode) + struct nameidata *nd, struct inode *const inode, + bool created) { umode_t dir_mode = nd->dir_mode; kuid_t dir_uid = nd->dir_uid; @@ -1230,7 +1231,9 @@ static int may_create_in_sticky(struct user_namespace *mnt_userns, (!sysctl_protected_regular && S_ISREG(inode->i_mode)) || likely(!(dir_mode & S_ISVTX)) || uid_eq(i_uid_into_mnt(mnt_userns, inode), dir_uid) || - uid_eq(current_fsuid(), i_uid_into_mnt(mnt_userns, inode))) + uid_eq(current_fsuid(), i_uid_into_mnt(mnt_userns, inode)) || + (created && + capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FOWNER))) return 0; if (likely(dir_mode & 0002) || @@ -3496,7 +3499,8 @@ static int do_open(struct nameidata *nd, if (d_is_dir(nd->path.dentry)) return -EISDIR; error = may_create_in_sticky(mnt_userns, nd, - d_backing_inode(nd->path.dentry)); + d_backing_inode(nd->path.dentry), + (file->f_mode & FMODE_CREATED)); if (unlikely(error)) return error; }
On Wed, Jul 27, 2022 at 01:34:13PM +0200, Christian Brauner wrote: > On Tue, Jul 26, 2022 at 04:27:56PM -0400, Jeff Layton wrote: > > On Tue, 2022-07-26 at 16:23 -0400, Jeff Layton wrote: > > > NFS server is exporting a sticky directory (mode 01777) with root > > > squashing enabled. Client has protect_regular enabled and then tries to > > > open a file as root in that directory. File is created (with ownership > > > set to nobody:nobody) but the open syscall returns an error. > > > > > > The problem is may_create_in_sticky, which rejects the open even though > > > the file has already been created/opened. Only call may_create_in_sticky > > > if the file hasn't already been opened or created. > > > > > > Cc: Christian Brauner <brauner@kernel.org> > > > Link: https://bugzilla.redhat.com/show_bug.cgi?id=1976829 > > > Reported-by: Yongchen Yang <yoyang@redhat.com> > > > Signed-off-by: Jeff Layton <jlayton@kernel.org> > > > --- > > > fs/namei.c | 13 +++++++++---- > > > 1 file changed, 9 insertions(+), 4 deletions(-) > > > > > > diff --git a/fs/namei.c b/fs/namei.c > > > index 1f28d3f463c3..7480b6dc8d27 100644 > > > --- a/fs/namei.c > > > +++ b/fs/namei.c > > > @@ -3495,10 +3495,15 @@ static int do_open(struct nameidata *nd, > > > return -EEXIST; > > > if (d_is_dir(nd->path.dentry)) > > > return -EISDIR; > > > - error = may_create_in_sticky(mnt_userns, nd, > > > - d_backing_inode(nd->path.dentry)); > > > - if (unlikely(error)) > > > - return error; > > > + if (!(file->f_mode & (FMODE_OPENED | FMODE_CREATED))) { > > > + error = may_create_in_sticky(mnt_userns, nd, > > > + d_backing_inode(nd->path.dentry)); > > > + if (unlikely(error)) { > > > + printk("%s: f_mode=0x%x oflag=0x%x\n", > > > + __func__, file->f_mode, open_flag); > > > + return error; > > > + } > > > + } > > > } > > > if ((nd->flags & LOOKUP_DIRECTORY) && !d_can_lookup(nd->path.dentry)) > > > return -ENOTDIR; > > > > I'm pretty sure this patch is the wrong approach, actually, since it > > doesn't fix the regular (non-atomic) open codepath. Any thoughts on what > > Hey Jeff, > > I haven't quite understood why that won't work for the regular open > codepaths. I'm probably missing something obvious. > > > the right fix might be? > > When an actual creation has taken place - and not just a lookup - then > may_create_in_sticky() assumes that the owner of the inode matches > current_fsuid(). That'd would also be problematic on fat or in fact on > any fs where the actual inode->i_{g,u}id are based on e.g. uid/gid mount > options and not on current_fsuid(), I think? > > So in order to improve this we would need to work around that assumption > in some way. Either by skipping may_create_in_sticky() if the file got > created or by adapting may_create_in_sticky(). > > I only wonder whether skipping may_create_in_sticky() altogether might > be a bit too lax. One possibility that came to my mind might be to relax > this assumption when the file has been created and the creator has > CAP_FOWNER. > > So (not compile tested or in any way) sm like: > > diff --git a/fs/namei.c b/fs/namei.c > index 1f28d3f463c3..239e9f423346 100644 > --- a/fs/namei.c > +++ b/fs/namei.c > @@ -1221,7 +1221,8 @@ int may_linkat(struct user_namespace *mnt_userns, struct path *link) > * Returns 0 if the open is allowed, -ve on error. > */ > static int may_create_in_sticky(struct user_namespace *mnt_userns, > - struct nameidata *nd, struct inode *const inode) > + struct nameidata *nd, struct inode *const inode, > + bool created) > { > umode_t dir_mode = nd->dir_mode; > kuid_t dir_uid = nd->dir_uid; > @@ -1230,7 +1231,9 @@ static int may_create_in_sticky(struct user_namespace *mnt_userns, > (!sysctl_protected_regular && S_ISREG(inode->i_mode)) || > likely(!(dir_mode & S_ISVTX)) || > uid_eq(i_uid_into_mnt(mnt_userns, inode), dir_uid) || > - uid_eq(current_fsuid(), i_uid_into_mnt(mnt_userns, inode))) > + uid_eq(current_fsuid(), i_uid_into_mnt(mnt_userns, inode)) || > + (created && > + capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FOWNER))) Sorry, this should be inode_owner_or_capable(mnt_userns, inode) > return 0; > > if (likely(dir_mode & 0002) || > @@ -3496,7 +3499,8 @@ static int do_open(struct nameidata *nd, > if (d_is_dir(nd->path.dentry)) > return -EISDIR; > error = may_create_in_sticky(mnt_userns, nd, > - d_backing_inode(nd->path.dentry)); > + d_backing_inode(nd->path.dentry), > + (file->f_mode & FMODE_CREATED)); > if (unlikely(error)) > return error; > }
On Wed, 2022-07-27 at 13:34 +0200, Christian Brauner wrote: > On Tue, Jul 26, 2022 at 04:27:56PM -0400, Jeff Layton wrote: > > On Tue, 2022-07-26 at 16:23 -0400, Jeff Layton wrote: > > > NFS server is exporting a sticky directory (mode 01777) with root > > > squashing enabled. Client has protect_regular enabled and then tries to > > > open a file as root in that directory. File is created (with ownership > > > set to nobody:nobody) but the open syscall returns an error. > > > > > > The problem is may_create_in_sticky, which rejects the open even though > > > the file has already been created/opened. Only call may_create_in_sticky > > > if the file hasn't already been opened or created. > > > > > > Cc: Christian Brauner <brauner@kernel.org> > > > Link: https://bugzilla.redhat.com/show_bug.cgi?id=1976829 > > > Reported-by: Yongchen Yang <yoyang@redhat.com> > > > Signed-off-by: Jeff Layton <jlayton@kernel.org> > > > --- > > > fs/namei.c | 13 +++++++++---- > > > 1 file changed, 9 insertions(+), 4 deletions(-) > > > > > > diff --git a/fs/namei.c b/fs/namei.c > > > index 1f28d3f463c3..7480b6dc8d27 100644 > > > --- a/fs/namei.c > > > +++ b/fs/namei.c > > > @@ -3495,10 +3495,15 @@ static int do_open(struct nameidata *nd, > > > return -EEXIST; > > > if (d_is_dir(nd->path.dentry)) > > > return -EISDIR; > > > - error = may_create_in_sticky(mnt_userns, nd, > > > - d_backing_inode(nd->path.dentry)); > > > - if (unlikely(error)) > > > - return error; > > > + if (!(file->f_mode & (FMODE_OPENED | FMODE_CREATED))) { > > > + error = may_create_in_sticky(mnt_userns, nd, > > > + d_backing_inode(nd->path.dentry)); > > > + if (unlikely(error)) { > > > + printk("%s: f_mode=0x%x oflag=0x%x\n", > > > + __func__, file->f_mode, open_flag); > > > + return error; > > > + } > > > + } > > > } > > > if ((nd->flags & LOOKUP_DIRECTORY) && !d_can_lookup(nd->path.dentry)) > > > return -ENOTDIR; > > > > I'm pretty sure this patch is the wrong approach, actually, since it > > doesn't fix the regular (non-atomic) open codepath. Any thoughts on what > > Hey Jeff, > > I haven't quite understood why that won't work for the regular open > codepaths. I'm probably missing something obvious. > In the normal open codepaths, FMODE_OPENED | FMODE_CREATED are still clear. If we're not doing an atomic_open (i.e. the dentry doesn't exist yet or is negative), then nothing really happens until you get to the vfs_open call. > > the right fix might be? > > When an actual creation has taken place - and not just a lookup - then > may_create_in_sticky() assumes that the owner of the inode matches > current_fsuid(). That'd would also be problematic on fat or in fact on > any fs where the actual inode->i_{g,u}id are based on e.g. uid/gid mount > options and not on current_fsuid(), I think? > > So in order to improve this we would need to work around that assumption > in some way. Either by skipping may_create_in_sticky() if the file got > created or by adapting may_create_in_sticky(). > > I only wonder whether skipping may_create_in_sticky() altogether might > be a bit too lax. One possibility that came to my mind might be to relax > this assumption when the file has been created and the creator has > CAP_FOWNER. > That may be the best option. I'll tinker around with that and see if I can get it to work. Thanks for the suggestion. > So (not compile tested or in any way) sm like: > > diff --git a/fs/namei.c b/fs/namei.c > index 1f28d3f463c3..239e9f423346 100644 > --- a/fs/namei.c > +++ b/fs/namei.c > @@ -1221,7 +1221,8 @@ int may_linkat(struct user_namespace *mnt_userns, struct path *link) > * Returns 0 if the open is allowed, -ve on error. > */ > static int may_create_in_sticky(struct user_namespace *mnt_userns, > - struct nameidata *nd, struct inode *const inode) > + struct nameidata *nd, struct inode *const inode, > + bool created) > { > umode_t dir_mode = nd->dir_mode; > kuid_t dir_uid = nd->dir_uid; > @@ -1230,7 +1231,9 @@ static int may_create_in_sticky(struct user_namespace *mnt_userns, > (!sysctl_protected_regular && S_ISREG(inode->i_mode)) || > likely(!(dir_mode & S_ISVTX)) || > uid_eq(i_uid_into_mnt(mnt_userns, inode), dir_uid) || > - uid_eq(current_fsuid(), i_uid_into_mnt(mnt_userns, inode))) > + uid_eq(current_fsuid(), i_uid_into_mnt(mnt_userns, inode)) || > + (created && > + capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FOWNER))) > return 0; > > if (likely(dir_mode & 0002) || > @@ -3496,7 +3499,8 @@ static int do_open(struct nameidata *nd, > if (d_is_dir(nd->path.dentry)) > return -EISDIR; > error = may_create_in_sticky(mnt_userns, nd, > - d_backing_inode(nd->path.dentry)); > + d_backing_inode(nd->path.dentry), > + (file->f_mode & FMODE_CREATED)); > if (unlikely(error)) > return error; > } I think that still won't fix it in the normal open codepath. FMODE_CREATED won't be set, so this will just end up failing again.
On Wed, Jul 27, 2022 at 08:04:34AM -0400, Jeff Layton wrote: > On Wed, 2022-07-27 at 13:34 +0200, Christian Brauner wrote: > > On Tue, Jul 26, 2022 at 04:27:56PM -0400, Jeff Layton wrote: > > > On Tue, 2022-07-26 at 16:23 -0400, Jeff Layton wrote: > > > > NFS server is exporting a sticky directory (mode 01777) with root > > > > squashing enabled. Client has protect_regular enabled and then tries to > > > > open a file as root in that directory. File is created (with ownership > > > > set to nobody:nobody) but the open syscall returns an error. > > > > > > > > The problem is may_create_in_sticky, which rejects the open even though > > > > the file has already been created/opened. Only call may_create_in_sticky > > > > if the file hasn't already been opened or created. > > > > > > > > Cc: Christian Brauner <brauner@kernel.org> > > > > Link: https://bugzilla.redhat.com/show_bug.cgi?id=1976829 > > > > Reported-by: Yongchen Yang <yoyang@redhat.com> > > > > Signed-off-by: Jeff Layton <jlayton@kernel.org> > > > > --- > > > > fs/namei.c | 13 +++++++++---- > > > > 1 file changed, 9 insertions(+), 4 deletions(-) > > > > > > > > diff --git a/fs/namei.c b/fs/namei.c > > > > index 1f28d3f463c3..7480b6dc8d27 100644 > > > > --- a/fs/namei.c > > > > +++ b/fs/namei.c > > > > @@ -3495,10 +3495,15 @@ static int do_open(struct nameidata *nd, > > > > return -EEXIST; > > > > if (d_is_dir(nd->path.dentry)) > > > > return -EISDIR; > > > > - error = may_create_in_sticky(mnt_userns, nd, > > > > - d_backing_inode(nd->path.dentry)); > > > > - if (unlikely(error)) > > > > - return error; > > > > + if (!(file->f_mode & (FMODE_OPENED | FMODE_CREATED))) { > > > > + error = may_create_in_sticky(mnt_userns, nd, > > > > + d_backing_inode(nd->path.dentry)); > > > > + if (unlikely(error)) { > > > > + printk("%s: f_mode=0x%x oflag=0x%x\n", > > > > + __func__, file->f_mode, open_flag); > > > > + return error; > > > > + } > > > > + } > > > > } > > > > if ((nd->flags & LOOKUP_DIRECTORY) && !d_can_lookup(nd->path.dentry)) > > > > return -ENOTDIR; > > > > > > I'm pretty sure this patch is the wrong approach, actually, since it > > > doesn't fix the regular (non-atomic) open codepath. Any thoughts on what > > > > Hey Jeff, > > > > I haven't quite understood why that won't work for the regular open > > codepaths. I'm probably missing something obvious. > > > > In the normal open codepaths, FMODE_OPENED | FMODE_CREATED are still > clear. If we're not doing an atomic_open (i.e. the dentry doesn't exist > yet or is negative), then nothing really happens until you get to the > vfs_open call. Hm, so for atomic open with O_CREAT it's: path_openat() -> open_last_lookups() -> lookup_open() /* * This is ->atomic_open() and FMODE_CREATED is set in the fs so * for NFS it's done in: * fs/nfs/dir.c: file->f_mode |= FMODE_CREATED; */ -> atomic_open() and for regular O_CREAT open it's: path_openat() -> open_last_lookups() -> lookup_open() { if (!dentry->d_inode && (open_flag & O_CREAT)) { file->f_mode |= FMODE_CREATED; } and that should all get surfaced to: path_openat() -> do_open() -> may_create_in_sticky() ?
On Wed, 2022-07-27 at 14:32 +0200, Christian Brauner wrote: > On Wed, Jul 27, 2022 at 08:04:34AM -0400, Jeff Layton wrote: > > On Wed, 2022-07-27 at 13:34 +0200, Christian Brauner wrote: > > > On Tue, Jul 26, 2022 at 04:27:56PM -0400, Jeff Layton wrote: > > > > On Tue, 2022-07-26 at 16:23 -0400, Jeff Layton wrote: > > > > > NFS server is exporting a sticky directory (mode 01777) with root > > > > > squashing enabled. Client has protect_regular enabled and then tries to > > > > > open a file as root in that directory. File is created (with ownership > > > > > set to nobody:nobody) but the open syscall returns an error. > > > > > > > > > > The problem is may_create_in_sticky, which rejects the open even though > > > > > the file has already been created/opened. Only call may_create_in_sticky > > > > > if the file hasn't already been opened or created. > > > > > > > > > > Cc: Christian Brauner <brauner@kernel.org> > > > > > Link: https://bugzilla.redhat.com/show_bug.cgi?id=1976829 > > > > > Reported-by: Yongchen Yang <yoyang@redhat.com> > > > > > Signed-off-by: Jeff Layton <jlayton@kernel.org> > > > > > --- > > > > > fs/namei.c | 13 +++++++++---- > > > > > 1 file changed, 9 insertions(+), 4 deletions(-) > > > > > > > > > > diff --git a/fs/namei.c b/fs/namei.c > > > > > index 1f28d3f463c3..7480b6dc8d27 100644 > > > > > --- a/fs/namei.c > > > > > +++ b/fs/namei.c > > > > > @@ -3495,10 +3495,15 @@ static int do_open(struct nameidata *nd, > > > > > return -EEXIST; > > > > > if (d_is_dir(nd->path.dentry)) > > > > > return -EISDIR; > > > > > - error = may_create_in_sticky(mnt_userns, nd, > > > > > - d_backing_inode(nd->path.dentry)); > > > > > - if (unlikely(error)) > > > > > - return error; > > > > > + if (!(file->f_mode & (FMODE_OPENED | FMODE_CREATED))) { > > > > > + error = may_create_in_sticky(mnt_userns, nd, > > > > > + d_backing_inode(nd->path.dentry)); > > > > > + if (unlikely(error)) { > > > > > + printk("%s: f_mode=0x%x oflag=0x%x\n", > > > > > + __func__, file->f_mode, open_flag); > > > > > + return error; > > > > > + } > > > > > + } > > > > > } > > > > > if ((nd->flags & LOOKUP_DIRECTORY) && !d_can_lookup(nd->path.dentry)) > > > > > return -ENOTDIR; > > > > > > > > I'm pretty sure this patch is the wrong approach, actually, since it > > > > doesn't fix the regular (non-atomic) open codepath. Any thoughts on what > > > > > > Hey Jeff, > > > > > > I haven't quite understood why that won't work for the regular open > > > codepaths. I'm probably missing something obvious. > > > > > > > In the normal open codepaths, FMODE_OPENED | FMODE_CREATED are still > > clear. If we're not doing an atomic_open (i.e. the dentry doesn't exist > > yet or is negative), then nothing really happens until you get to the > > vfs_open call. > > Hm, so for atomic open with O_CREAT it's: > > path_openat() > -> open_last_lookups() > -> lookup_open() > /* > * This is ->atomic_open() and FMODE_CREATED is set in the fs so > * for NFS it's done in: > * fs/nfs/dir.c: file->f_mode |= FMODE_CREATED; > */ > -> atomic_open() > > and for regular O_CREAT open it's: > > path_openat() > -> open_last_lookups() > -> lookup_open() > { > if (!dentry->d_inode && (open_flag & O_CREAT)) { > file->f_mode |= FMODE_CREATED; > } > > > and that should all get surfaced to: > > path_openat() > -> do_open() > -> may_create_in_sticky() > > ? Basically, yes, but we also need to deal with the case where the file already exists. That's being denied currently too and I don't think it should be.
On Wed, Jul 27, 2022 at 09:00:46AM -0400, Jeff Layton wrote: > On Wed, 2022-07-27 at 14:32 +0200, Christian Brauner wrote: > > On Wed, Jul 27, 2022 at 08:04:34AM -0400, Jeff Layton wrote: > > > On Wed, 2022-07-27 at 13:34 +0200, Christian Brauner wrote: > > > > On Tue, Jul 26, 2022 at 04:27:56PM -0400, Jeff Layton wrote: > > > > > On Tue, 2022-07-26 at 16:23 -0400, Jeff Layton wrote: > > > > > > NFS server is exporting a sticky directory (mode 01777) with root > > > > > > squashing enabled. Client has protect_regular enabled and then tries to > > > > > > open a file as root in that directory. File is created (with ownership > > > > > > set to nobody:nobody) but the open syscall returns an error. > > > > > > > > > > > > The problem is may_create_in_sticky, which rejects the open even though > > > > > > the file has already been created/opened. Only call may_create_in_sticky > > > > > > if the file hasn't already been opened or created. > > > > > > > > > > > > Cc: Christian Brauner <brauner@kernel.org> > > > > > > Link: https://bugzilla.redhat.com/show_bug.cgi?id=1976829 > > > > > > Reported-by: Yongchen Yang <yoyang@redhat.com> > > > > > > Signed-off-by: Jeff Layton <jlayton@kernel.org> > > > > > > --- > > > > > > fs/namei.c | 13 +++++++++---- > > > > > > 1 file changed, 9 insertions(+), 4 deletions(-) > > > > > > > > > > > > diff --git a/fs/namei.c b/fs/namei.c > > > > > > index 1f28d3f463c3..7480b6dc8d27 100644 > > > > > > --- a/fs/namei.c > > > > > > +++ b/fs/namei.c > > > > > > @@ -3495,10 +3495,15 @@ static int do_open(struct nameidata *nd, > > > > > > return -EEXIST; > > > > > > if (d_is_dir(nd->path.dentry)) > > > > > > return -EISDIR; > > > > > > - error = may_create_in_sticky(mnt_userns, nd, > > > > > > - d_backing_inode(nd->path.dentry)); > > > > > > - if (unlikely(error)) > > > > > > - return error; > > > > > > + if (!(file->f_mode & (FMODE_OPENED | FMODE_CREATED))) { > > > > > > + error = may_create_in_sticky(mnt_userns, nd, > > > > > > + d_backing_inode(nd->path.dentry)); > > > > > > + if (unlikely(error)) { > > > > > > + printk("%s: f_mode=0x%x oflag=0x%x\n", > > > > > > + __func__, file->f_mode, open_flag); > > > > > > + return error; > > > > > > + } > > > > > > + } > > > > > > } > > > > > > if ((nd->flags & LOOKUP_DIRECTORY) && !d_can_lookup(nd->path.dentry)) > > > > > > return -ENOTDIR; > > > > > > > > > > I'm pretty sure this patch is the wrong approach, actually, since it > > > > > doesn't fix the regular (non-atomic) open codepath. Any thoughts on what > > > > > > > > Hey Jeff, > > > > > > > > I haven't quite understood why that won't work for the regular open > > > > codepaths. I'm probably missing something obvious. > > > > > > > > > > In the normal open codepaths, FMODE_OPENED | FMODE_CREATED are still > > > clear. If we're not doing an atomic_open (i.e. the dentry doesn't exist > > > yet or is negative), then nothing really happens until you get to the > > > vfs_open call. > > > > Hm, so for atomic open with O_CREAT it's: > > > > path_openat() > > -> open_last_lookups() > > -> lookup_open() > > /* > > * This is ->atomic_open() and FMODE_CREATED is set in the fs so > > * for NFS it's done in: > > * fs/nfs/dir.c: file->f_mode |= FMODE_CREATED; > > */ > > -> atomic_open() > > > > and for regular O_CREAT open it's: > > > > path_openat() > > -> open_last_lookups() > > -> lookup_open() > > { > > if (!dentry->d_inode && (open_flag & O_CREAT)) { > > file->f_mode |= FMODE_CREATED; > > } > > > > > > and that should all get surfaced to: > > > > path_openat() > > -> do_open() > > -> may_create_in_sticky() > > > > ? > > Basically, yes, but we also need to deal with the case where the file > already exists. That's being denied currently too and I don't think it > should be. Yeah, that's the part I'm not sure I agree with (see other thread).
diff --git a/fs/namei.c b/fs/namei.c index 1f28d3f463c3..7480b6dc8d27 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -3495,10 +3495,15 @@ static int do_open(struct nameidata *nd, return -EEXIST; if (d_is_dir(nd->path.dentry)) return -EISDIR; - error = may_create_in_sticky(mnt_userns, nd, - d_backing_inode(nd->path.dentry)); - if (unlikely(error)) - return error; + if (!(file->f_mode & (FMODE_OPENED | FMODE_CREATED))) { + error = may_create_in_sticky(mnt_userns, nd, + d_backing_inode(nd->path.dentry)); + if (unlikely(error)) { + printk("%s: f_mode=0x%x oflag=0x%x\n", + __func__, file->f_mode, open_flag); + return error; + } + } } if ((nd->flags & LOOKUP_DIRECTORY) && !d_can_lookup(nd->path.dentry)) return -ENOTDIR;
NFS server is exporting a sticky directory (mode 01777) with root squashing enabled. Client has protect_regular enabled and then tries to open a file as root in that directory. File is created (with ownership set to nobody:nobody) but the open syscall returns an error. The problem is may_create_in_sticky, which rejects the open even though the file has already been created/opened. Only call may_create_in_sticky if the file hasn't already been opened or created. Cc: Christian Brauner <brauner@kernel.org> Link: https://bugzilla.redhat.com/show_bug.cgi?id=1976829 Reported-by: Yongchen Yang <yoyang@redhat.com> Signed-off-by: Jeff Layton <jlayton@kernel.org> --- fs/namei.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-)