| Message ID | 20240905135700.16394-1-luis.henriques@linux.dev (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [RFC,v2] ceph: ceph: fix out-of-bound array access when doing a file read | expand |
On 9/5/24 21:57, Luis Henriques (SUSE) wrote: > __ceph_sync_read() does not correctly handle reads when the inode size is > zero. It is easy to hit a NULL pointer dereference by continuously reading > a file while, on another client, we keep truncating and writing new data > into it. > > The NULL pointer dereference happens when the inode size is zero but the > read op returns some data (ceph_osdc_wait_request()). This will lead to > 'left' being set to a huge value due to the overflow in: > > left = i_size - off; > > and, in the loop that follows, the pages[] array being accessed beyond > num_pages. > > This patch fixes the issue simply by checking the inode size and returning > if it is zero, even if there was data from the read op. > > Link: https://tracker.ceph.com/issues/67524 > Fixes: 1065da21e5df ("ceph: stop copying to iter at EOF on sync reads") > Signed-off-by: Luis Henriques (SUSE) <luis.henriques@linux.dev> > --- > fs/ceph/file.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/fs/ceph/file.c b/fs/ceph/file.c > index 4b8d59ebda00..41d4eac128bb 100644 > --- a/fs/ceph/file.c > +++ b/fs/ceph/file.c > @@ -1066,7 +1066,7 @@ ssize_t __ceph_sync_read(struct inode *inode, loff_t *ki_pos, > if (ceph_inode_is_shutdown(inode)) > return -EIO; > > - if (!len) > + if (!len || !i_size) > return 0; > /* > * flush any page cache pages in this range. this > @@ -1154,6 +1154,9 @@ ssize_t __ceph_sync_read(struct inode *inode, loff_t *ki_pos, > doutc(cl, "%llu~%llu got %zd i_size %llu%s\n", off, len, > ret, i_size, (more ? " MORE" : "")); > > + if (i_size == 0) > + ret = 0; > + > /* Fix it to go to end of extent map */ > if (sparse && ret >= 0) > ret = ceph_sparse_ext_map_end(op); > Hi Luis, BTW, so in the following code: 1202 idx = 0; 1203 if (ret <= 0) 1204 left = 0; 1205 else if (off + ret > i_size) 1206 left = i_size - off; 1207 else 1208 left = ret; The 'ret' should be larger than '0', right ? If so we do not check anf fix it in the 'else if' branch instead? Because currently the read path code won't exit directly and keep retrying to read if it found that the real content length is longer than the local 'i_size'. Again I am afraid your current fix will break the MIX filelock semantic ? Thanks - Xiubo
On Fri, Sep 06 2024, Xiubo Li wrote: > On 9/5/24 21:57, Luis Henriques (SUSE) wrote: >> __ceph_sync_read() does not correctly handle reads when the inode size is >> zero. It is easy to hit a NULL pointer dereference by continuously reading >> a file while, on another client, we keep truncating and writing new data >> into it. >> >> The NULL pointer dereference happens when the inode size is zero but the >> read op returns some data (ceph_osdc_wait_request()). This will lead to >> 'left' being set to a huge value due to the overflow in: >> >> left = i_size - off; >> >> and, in the loop that follows, the pages[] array being accessed beyond >> num_pages. >> >> This patch fixes the issue simply by checking the inode size and returning >> if it is zero, even if there was data from the read op. >> >> Link: https://tracker.ceph.com/issues/67524 >> Fixes: 1065da21e5df ("ceph: stop copying to iter at EOF on sync reads") >> Signed-off-by: Luis Henriques (SUSE) <luis.henriques@linux.dev> >> --- >> fs/ceph/file.c | 5 ++++- >> 1 file changed, 4 insertions(+), 1 deletion(-) >> >> diff --git a/fs/ceph/file.c b/fs/ceph/file.c >> index 4b8d59ebda00..41d4eac128bb 100644 >> --- a/fs/ceph/file.c >> +++ b/fs/ceph/file.c >> @@ -1066,7 +1066,7 @@ ssize_t __ceph_sync_read(struct inode *inode, loff_t *ki_pos, >> if (ceph_inode_is_shutdown(inode)) >> return -EIO; >> - if (!len) >> + if (!len || !i_size) >> return 0; >> /* >> * flush any page cache pages in this range. this >> @@ -1154,6 +1154,9 @@ ssize_t __ceph_sync_read(struct inode *inode, loff_t *ki_pos, >> doutc(cl, "%llu~%llu got %zd i_size %llu%s\n", off, len, >> ret, i_size, (more ? " MORE" : "")); >> + if (i_size == 0) >> + ret = 0; >> + >> /* Fix it to go to end of extent map */ >> if (sparse && ret >= 0) >> ret = ceph_sparse_ext_map_end(op); >> > Hi Luis, > > BTW, so in the following code: > > 1202 idx = 0; > 1203 if (ret <= 0) > 1204 left = 0; > 1205 else if (off + ret > i_size) > 1206 left = i_size - off; > 1207 else > 1208 left = ret; > > The 'ret' should be larger than '0', right ? Right. (Which means we read something from the file.) > If so we do not check anf fix it in the 'else if' branch instead? Yes, and then we'll have: left = i_size - off; and because 'i_size' is 0, so 'left' will be set to 0xffffffffff... And the loop that follows: while (left > 0) { ... } will keep looping until we get a NULL pointer. Have you tried the reproducer? Cheers,
On 9/6/24 19:30, Luis Henriques wrote: > On Fri, Sep 06 2024, Xiubo Li wrote: > >> On 9/5/24 21:57, Luis Henriques (SUSE) wrote: >>> __ceph_sync_read() does not correctly handle reads when the inode size is >>> zero. It is easy to hit a NULL pointer dereference by continuously reading >>> a file while, on another client, we keep truncating and writing new data >>> into it. >>> >>> The NULL pointer dereference happens when the inode size is zero but the >>> read op returns some data (ceph_osdc_wait_request()). This will lead to >>> 'left' being set to a huge value due to the overflow in: >>> >>> left = i_size - off; >>> >>> and, in the loop that follows, the pages[] array being accessed beyond >>> num_pages. >>> >>> This patch fixes the issue simply by checking the inode size and returning >>> if it is zero, even if there was data from the read op. >>> >>> Link: https://tracker.ceph.com/issues/67524 >>> Fixes: 1065da21e5df ("ceph: stop copying to iter at EOF on sync reads") >>> Signed-off-by: Luis Henriques (SUSE) <luis.henriques@linux.dev> >>> --- >>> fs/ceph/file.c | 5 ++++- >>> 1 file changed, 4 insertions(+), 1 deletion(-) >>> >>> diff --git a/fs/ceph/file.c b/fs/ceph/file.c >>> index 4b8d59ebda00..41d4eac128bb 100644 >>> --- a/fs/ceph/file.c >>> +++ b/fs/ceph/file.c >>> @@ -1066,7 +1066,7 @@ ssize_t __ceph_sync_read(struct inode *inode, loff_t *ki_pos, >>> if (ceph_inode_is_shutdown(inode)) >>> return -EIO; >>> - if (!len) >>> + if (!len || !i_size) >>> return 0; >>> /* >>> * flush any page cache pages in this range. this >>> @@ -1154,6 +1154,9 @@ ssize_t __ceph_sync_read(struct inode *inode, loff_t *ki_pos, >>> doutc(cl, "%llu~%llu got %zd i_size %llu%s\n", off, len, >>> ret, i_size, (more ? " MORE" : "")); >>> + if (i_size == 0) >>> + ret = 0; >>> + >>> /* Fix it to go to end of extent map */ >>> if (sparse && ret >= 0) >>> ret = ceph_sparse_ext_map_end(op); >>> >> Hi Luis, >> >> BTW, so in the following code: >> >> 1202 idx = 0; >> 1203 if (ret <= 0) >> 1204 left = 0; >> 1205 else if (off + ret > i_size) >> 1206 left = i_size - off; >> 1207 else >> 1208 left = ret; >> >> The 'ret' should be larger than '0', right ? > Right. (Which means we read something from the file.) > >> If so we do not check anf fix it in the 'else if' branch instead? > Yes, and then we'll have: > > left = i_size - off; > > and because 'i_size' is 0, so 'left' will be set to 0xffffffffff... > And the loop that follows: > > while (left > 0) { > ... > } > > will keep looping until we get a NULL pointer. Have you tried the > reproducer? Hi Luis, Not yet, and recently I haven't get a chance to do that for the reason as you know. Thanks - Xiubo > Cheers,
On Fri, Sep 06 2024, Xiubo Li wrote: > On 9/6/24 19:30, Luis Henriques wrote: >> On Fri, Sep 06 2024, Xiubo Li wrote: >> >>> On 9/5/24 21:57, Luis Henriques (SUSE) wrote: >>>> __ceph_sync_read() does not correctly handle reads when the inode size is >>>> zero. It is easy to hit a NULL pointer dereference by continuously reading >>>> a file while, on another client, we keep truncating and writing new data >>>> into it. >>>> >>>> The NULL pointer dereference happens when the inode size is zero but the >>>> read op returns some data (ceph_osdc_wait_request()). This will lead to >>>> 'left' being set to a huge value due to the overflow in: >>>> >>>> left = i_size - off; >>>> >>>> and, in the loop that follows, the pages[] array being accessed beyond >>>> num_pages. >>>> >>>> This patch fixes the issue simply by checking the inode size and returning >>>> if it is zero, even if there was data from the read op. >>>> >>>> Link: https://tracker.ceph.com/issues/67524 >>>> Fixes: 1065da21e5df ("ceph: stop copying to iter at EOF on sync reads") >>>> Signed-off-by: Luis Henriques (SUSE) <luis.henriques@linux.dev> >>>> --- >>>> fs/ceph/file.c | 5 ++++- >>>> 1 file changed, 4 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/fs/ceph/file.c b/fs/ceph/file.c >>>> index 4b8d59ebda00..41d4eac128bb 100644 >>>> --- a/fs/ceph/file.c >>>> +++ b/fs/ceph/file.c >>>> @@ -1066,7 +1066,7 @@ ssize_t __ceph_sync_read(struct inode *inode, loff_t *ki_pos, >>>> if (ceph_inode_is_shutdown(inode)) >>>> return -EIO; >>>> - if (!len) >>>> + if (!len || !i_size) >>>> return 0; >>>> /* >>>> * flush any page cache pages in this range. this >>>> @@ -1154,6 +1154,9 @@ ssize_t __ceph_sync_read(struct inode *inode, loff_t *ki_pos, >>>> doutc(cl, "%llu~%llu got %zd i_size %llu%s\n", off, len, >>>> ret, i_size, (more ? " MORE" : "")); >>>> + if (i_size == 0) >>>> + ret = 0; >>>> + >>>> /* Fix it to go to end of extent map */ >>>> if (sparse && ret >= 0) >>>> ret = ceph_sparse_ext_map_end(op); >>>> >>> Hi Luis, >>> >>> BTW, so in the following code: >>> >>> 1202 idx = 0; >>> 1203 if (ret <= 0) >>> 1204 left = 0; >>> 1205 else if (off + ret > i_size) >>> 1206 left = i_size - off; >>> 1207 else >>> 1208 left = ret; >>> >>> The 'ret' should be larger than '0', right ? >> Right. (Which means we read something from the file.) >> >>> If so we do not check anf fix it in the 'else if' branch instead? >> Yes, and then we'll have: >> >> left = i_size - off; >> >> and because 'i_size' is 0, so 'left' will be set to 0xffffffffff... >> And the loop that follows: >> >> while (left > 0) { >> ... >> } >> >> will keep looping until we get a NULL pointer. Have you tried the >> reproducer? > > Hi Luis, > > Not yet, and recently I haven't get a chance to do that for the reason as you > know. Hi Xiubo, I know you've been busy, but I was wondering if you (or someone else) had a chance to have a look at this. It's pretty easy to reproduce, and it has been seen in production. Any chances of getting some more feedback on this fix? Cheers,
Hi Xiubo, Hi Ilya, On Mon, Sep 30 2024, Luis Henriques wrote: [...] > Hi Xiubo, > > I know you've been busy, but I was wondering if you (or someone else) had > a chance to have a look at this. It's pretty easy to reproduce, and it > has been seen in production. Any chances of getting some more feedback on > this fix? It has been a while since I first reported this issue. Taking the risk of being "that annoying guy", I'd like to ping you again on this. I've managed to reproduce the issue very easily, and it's also being triggered very frequently in production. Any news? Cheers,
CC Alex Hi Luis, Alex will take over it and help push it recently. I am a bit busy with my new things these days. BTW, if possible please join 'ceph' workspace's #cephfs slack channel and you could push it faster there ? Thanks - Xiubo 在 2024/11/4 22:34, Luis Henriques 写道: > Hi Xiubo, Hi Ilya, > > On Mon, Sep 30 2024, Luis Henriques wrote: > [...] >> Hi Xiubo, >> >> I know you've been busy, but I was wondering if you (or someone else) had >> a chance to have a look at this. It's pretty easy to reproduce, and it >> has been seen in production. Any chances of getting some more feedback on >> this fix? > It has been a while since I first reported this issue. Taking the risk of > being "that annoying guy", I'd like to ping you again on this. I've > managed to reproduce the issue very easily, and it's also being triggered > very frequently in production. Any news? > > Cheers,
Hi Xiubo! On Tue, Nov 05 2024, Xiubo Li wrote: > CC Alex > > Hi Luis, > > Alex will take over it and help push it recently. I am a bit busy with my new > things these days. Thanks a lot. I think the difficult bit to understand (for me, at least!) are any MDS side-effects, as you earlier mentioned the filelocking semantics. I'm not sure if/how this patch may cause troubles there. > BTW, if possible please join 'ceph' workspace's #cephfs slack channel and you > could push it faster there ? I believe that channel is bridged to IRC (OFTC network), where I'm already lurking (nick 'henrix'). And I see you have already ping'ed others there. However, I'm currently on PTO, so my replies there may be asynchronous :-) Cheers,
Hi Xiubo, > BTW, so in the following code: > > 1202 idx = 0; > 1203 if (ret <= 0) > 1204 left = 0; > 1205 else if (off + ret > i_size) > 1206 left = i_size - off; > 1207 else > 1208 left = ret; > > The 'ret' should be larger than '0', right ? > > If so we do not check anf fix it in the 'else if' branch instead? > > Because currently the read path code won't exit directly and keep > retrying to read if it found that the real content length is longer than > the local 'i_size'. > > Again I am afraid your current fix will break the MIX filelock semantic ? Do you think changing left to ssize_t instead of size_t will fix the problem? diff --git a/fs/ceph/file.c b/fs/ceph/file.c index 4b8d59ebda00..f8955773bdd7 100644 --- a/fs/ceph/file.c +++ b/fs/ceph/file.c @@ -1066,7 +1066,7 @@ ssize_t __ceph_sync_read(struct inode *inode, loff_t *ki_pos, if (ceph_inode_is_shutdown(inode)) return -EIO; - if (!len) + if (!len || !i_size) return 0; /* * flush any page cache pages in this range. this @@ -1087,7 +1087,7 @@ ssize_t __ceph_sync_read(struct inode *inode, loff_t *ki_pos, size_t page_off; bool more; int idx; - size_t left; + ssize_t left; struct ceph_osd_req_op *op; u64 read_off = off; u64 read_len = len;
(CC'ing Alex) On Wed, Nov 06 2024, Goldwyn Rodrigues wrote: > Hi Xiubo, > >> BTW, so in the following code: >> >> 1202 idx = 0; >> 1203 if (ret <= 0) >> 1204 left = 0; >> 1205 else if (off + ret > i_size) >> 1206 left = i_size - off; >> 1207 else >> 1208 left = ret; >> >> The 'ret' should be larger than '0', right ? >> >> If so we do not check anf fix it in the 'else if' branch instead? >> >> Because currently the read path code won't exit directly and keep >> retrying to read if it found that the real content length is longer than >> the local 'i_size'. >> >> Again I am afraid your current fix will break the MIX filelock semantic ? > > Do you think changing left to ssize_t instead of size_t will > fix the problem? > > diff --git a/fs/ceph/file.c b/fs/ceph/file.c > index 4b8d59ebda00..f8955773bdd7 100644 > --- a/fs/ceph/file.c > +++ b/fs/ceph/file.c > @@ -1066,7 +1066,7 @@ ssize_t __ceph_sync_read(struct inode *inode, loff_t *ki_pos, > if (ceph_inode_is_shutdown(inode)) > return -EIO; > > - if (!len) > + if (!len || !i_size) > return 0; > /* > * flush any page cache pages in this range. this > @@ -1087,7 +1087,7 @@ ssize_t __ceph_sync_read(struct inode *inode, loff_t *ki_pos, > size_t page_off; > bool more; > int idx; > - size_t left; > + ssize_t left; > struct ceph_osd_req_op *op; > u64 read_off = off; > u64 read_len = len; > I *think* (although I haven't tested it) that you're patch should work as well. But I also think it's a bit more hacky: the overflow will still be there: if (ret <= 0) left = 0; else if (off + ret > i_size) left = i_size - off; else left = ret; while (left > 0) { // ... } If 'i_size' is '0', 'left' (which is now signed) will now have a negative value in the 'else if' branch and the loop that follows will not be executed. My version will simply set 'ret' to '0' before this 'if' construct. So, in my opinion, what needs to be figured out is whether this will cause problems on the MDS side or not. Because on the kernel client, it should be safe to ignore reads to an inode that has size set to '0', even if there's already data available to be read. Eventually, the inode metadata will get updated and by then we can retry the read. Unfortunately, the MDS continues to be a huge black box for me and the locking code in particular is very tricky. I'd rather defer this for anyone that is familiar with the code. Cheers,
Hi, Folks.
AFAIK there is no side effect that can affect MDS with this fix.
This crash happens following this patch
"1065da21e5df9d843d2c5165d5d576be000142a6" "ceph: stop copying to iter
at EOF on sync reads".
Per your fix Luis, it seems to address only the cases when i_size goes
to zero but can happen anytime the `i_size` goes below `off`.
I propose fixing it this way:
diff --git a/fs/ceph/file.c b/fs/ceph/file.c
index 4b8d59ebda00..19b084212fee 100644
--- a/fs/ceph/file.c
+++ b/fs/ceph/file.c
@@ -1066,7 +1066,7 @@ ssize_t __ceph_sync_read(struct inode *inode,
loff_t *ki_pos,
if (ceph_inode_is_shutdown(inode))
return -EIO;
- if (!len)
+ if (!len || !i_size)
return 0;
/*
* flush any page cache pages in this range. this
@@ -1200,12 +1200,11 @@ ssize_t __ceph_sync_read(struct inode *inode,
loff_t *ki_pos,
}
idx = 0;
- if (ret <= 0)
- left = 0;
- else if (off + ret > i_size)
- left = i_size - off;
+ if (off + ret > i_size)
+ left = (i_size > off) ? i_size - off : 0;
else
- left = ret;
+ left = (ret > 0) ? ret : 0;
+
while (left > 0) {
size_t plen, copied;
On Thu, Nov 7, 2024 at 1:09 PM Luis Henriques <luis.henriques@linux.dev> wrote:
>
> (CC'ing Alex)
>
> On Wed, Nov 06 2024, Goldwyn Rodrigues wrote:
>
> > Hi Xiubo,
> >
> >> BTW, so in the following code:
> >>
> >> 1202 idx = 0;
> >> 1203 if (ret <= 0)
> >> 1204 left = 0;
> >> 1205 else if (off + ret > i_size)
> >> 1206 left = i_size - off;
> >> 1207 else
> >> 1208 left = ret;
> >>
> >> The 'ret' should be larger than '0', right ?
> >>
> >> If so we do not check anf fix it in the 'else if' branch instead?
> >>
> >> Because currently the read path code won't exit directly and keep
> >> retrying to read if it found that the real content length is longer than
> >> the local 'i_size'.
> >>
> >> Again I am afraid your current fix will break the MIX filelock semantic ?
> >
> > Do you think changing left to ssize_t instead of size_t will
> > fix the problem?
> >
> > diff --git a/fs/ceph/file.c b/fs/ceph/file.c
> > index 4b8d59ebda00..f8955773bdd7 100644
> > --- a/fs/ceph/file.c
> > +++ b/fs/ceph/file.c
> > @@ -1066,7 +1066,7 @@ ssize_t __ceph_sync_read(struct inode *inode, loff_t *ki_pos,
> > if (ceph_inode_is_shutdown(inode))
> > return -EIO;
> >
> > - if (!len)
> > + if (!len || !i_size)
> > return 0;
> > /*
> > * flush any page cache pages in this range. this
> > @@ -1087,7 +1087,7 @@ ssize_t __ceph_sync_read(struct inode *inode, loff_t *ki_pos,
> > size_t page_off;
> > bool more;
> > int idx;
> > - size_t left;
> > + ssize_t left;
> > struct ceph_osd_req_op *op;
> > u64 read_off = off;
> > u64 read_len = len;
> >
>
> I *think* (although I haven't tested it) that you're patch should work as
> well. But I also think it's a bit more hacky: the overflow will still be
> there:
>
> if (ret <= 0)
> left = 0;
> else if (off + ret > i_size)
> left = i_size - off;
> else
> left = ret;
> while (left > 0) {
> // ...
> }
>
> If 'i_size' is '0', 'left' (which is now signed) will now have a negative
> value in the 'else if' branch and the loop that follows will not be
> executed. My version will simply set 'ret' to '0' before this 'if'
> construct.
>
> So, in my opinion, what needs to be figured out is whether this will cause
> problems on the MDS side or not. Because on the kernel client, it should
> be safe to ignore reads to an inode that has size set to '0', even if
> there's already data available to be read. Eventually, the inode metadata
> will get updated and by then we can retry the read.
>
> Unfortunately, the MDS continues to be a huge black box for me and the
> locking code in particular is very tricky. I'd rather defer this for
> anyone that is familiar with the code.
>
> Cheers,
> --
> Luís
>
Hi Alex, [ Thank you for looking into this. ] On Wed, Nov 27 2024, Alex Markuze wrote: > Hi, Folks. > AFAIK there is no side effect that can affect MDS with this fix. > This crash happens following this patch > "1065da21e5df9d843d2c5165d5d576be000142a6" "ceph: stop copying to iter > at EOF on sync reads". > > Per your fix Luis, it seems to address only the cases when i_size goes > to zero but can happen anytime the `i_size` goes below `off`. > I propose fixing it this way: Hmm... you're probably right. I didn't see this happening, but I guess it could indeed happen. > diff --git a/fs/ceph/file.c b/fs/ceph/file.c > index 4b8d59ebda00..19b084212fee 100644 > --- a/fs/ceph/file.c > +++ b/fs/ceph/file.c > @@ -1066,7 +1066,7 @@ ssize_t __ceph_sync_read(struct inode *inode, > loff_t *ki_pos, > if (ceph_inode_is_shutdown(inode)) > return -EIO; > > - if (!len) > + if (!len || !i_size) > return 0; > /* > * flush any page cache pages in this range. this > @@ -1200,12 +1200,11 @@ ssize_t __ceph_sync_read(struct inode *inode, > loff_t *ki_pos, > } > > idx = 0; > - if (ret <= 0) > - left = 0; Right now I don't have any means for testing this patch. However, I don't think this is completely correct. By removing the above condition you're discarding cases where an error has occurred (i.e. where ret is negative). Why not simply modify my patch and do: if (i_size < off) ret = 0; instead of: if (i_size == 0) ret = 0; ? (Again, totally untested!) Cheers,
I didn't discard it though :). I folded it into the `if` statement. I find the if else construct overly verbose and cumbersome. + left = (ret > 0) ? ret : 0; On Thu, Nov 28, 2024 at 7:43 PM Luis Henriques <luis.henriques@linux.dev> wrote: > > Hi Alex, > > [ Thank you for looking into this. ] > > On Wed, Nov 27 2024, Alex Markuze wrote: > > > Hi, Folks. > > AFAIK there is no side effect that can affect MDS with this fix. > > This crash happens following this patch > > "1065da21e5df9d843d2c5165d5d576be000142a6" "ceph: stop copying to iter > > at EOF on sync reads". > > > > Per your fix Luis, it seems to address only the cases when i_size goes > > to zero but can happen anytime the `i_size` goes below `off`. > > I propose fixing it this way: > > Hmm... you're probably right. I didn't see this happening, but I guess it > could indeed happen. > > > diff --git a/fs/ceph/file.c b/fs/ceph/file.c > > index 4b8d59ebda00..19b084212fee 100644 > > --- a/fs/ceph/file.c > > +++ b/fs/ceph/file.c > > @@ -1066,7 +1066,7 @@ ssize_t __ceph_sync_read(struct inode *inode, > > loff_t *ki_pos, > > if (ceph_inode_is_shutdown(inode)) > > return -EIO; > > > > - if (!len) > > + if (!len || !i_size) > > return 0; > > /* > > * flush any page cache pages in this range. this > > @@ -1200,12 +1200,11 @@ ssize_t __ceph_sync_read(struct inode *inode, > > loff_t *ki_pos, > > } > > > > idx = 0; > > - if (ret <= 0) > > - left = 0; > > Right now I don't have any means for testing this patch. However, I don't > think this is completely correct. By removing the above condition you're > discarding cases where an error has occurred (i.e. where ret is negative). > > Why not simply modify my patch and do: > > if (i_size < off) > ret = 0; > > instead of: > if (i_size == 0) > ret = 0; > > ? > > (Again, totally untested!) > > Cheers, > -- > Luís > > > - else if (off + ret > i_size) > > - left = i_size - off; > > + if (off + ret > i_size) > > + left = (i_size > off) ? i_size - off : 0; > > else > > - left = ret; > > + left = (ret > 0) ? ret : 0; > > + > > while (left > 0) { > > size_t plen, copied; > > > > > > On Thu, Nov 7, 2024 at 1:09 PM Luis Henriques <luis.henriques@linux.dev> wrote: > >> > >> (CC'ing Alex) > >> > >> On Wed, Nov 06 2024, Goldwyn Rodrigues wrote: > >> > >> > Hi Xiubo, > >> > > >> >> BTW, so in the following code: > >> >> > >> >> 1202 idx = 0; > >> >> 1203 if (ret <= 0) > >> >> 1204 left = 0; > >> >> 1205 else if (off + ret > i_size) > >> >> 1206 left = i_size - off; > >> >> 1207 else > >> >> 1208 left = ret; > >> >> > >> >> The 'ret' should be larger than '0', right ? > >> >> > >> >> If so we do not check anf fix it in the 'else if' branch instead? > >> >> > >> >> Because currently the read path code won't exit directly and keep > >> >> retrying to read if it found that the real content length is longer than > >> >> the local 'i_size'. > >> >> > >> >> Again I am afraid your current fix will break the MIX filelock semantic ? > >> > > >> > Do you think changing left to ssize_t instead of size_t will > >> > fix the problem? > >> > > >> > diff --git a/fs/ceph/file.c b/fs/ceph/file.c > >> > index 4b8d59ebda00..f8955773bdd7 100644 > >> > --- a/fs/ceph/file.c > >> > +++ b/fs/ceph/file.c > >> > @@ -1066,7 +1066,7 @@ ssize_t __ceph_sync_read(struct inode *inode, loff_t *ki_pos, > >> > if (ceph_inode_is_shutdown(inode)) > >> > return -EIO; > >> > > >> > - if (!len) > >> > + if (!len || !i_size) > >> > return 0; > >> > /* > >> > * flush any page cache pages in this range. this > >> > @@ -1087,7 +1087,7 @@ ssize_t __ceph_sync_read(struct inode *inode, loff_t *ki_pos, > >> > size_t page_off; > >> > bool more; > >> > int idx; > >> > - size_t left; > >> > + ssize_t left; > >> > struct ceph_osd_req_op *op; > >> > u64 read_off = off; > >> > u64 read_len = len; > >> > > >> > >> I *think* (although I haven't tested it) that you're patch should work as > >> well. But I also think it's a bit more hacky: the overflow will still be > >> there: > >> > >> if (ret <= 0) > >> left = 0; > >> else if (off + ret > i_size) > >> left = i_size - off; > >> else > >> left = ret; > >> while (left > 0) { > >> // ... > >> } > >> > >> If 'i_size' is '0', 'left' (which is now signed) will now have a negative > >> value in the 'else if' branch and the loop that follows will not be > >> executed. My version will simply set 'ret' to '0' before this 'if' > >> construct. > >> > >> So, in my opinion, what needs to be figured out is whether this will cause > >> problems on the MDS side or not. Because on the kernel client, it should > >> be safe to ignore reads to an inode that has size set to '0', even if > >> there's already data available to be read. Eventually, the inode metadata > >> will get updated and by then we can retry the read. > >> > >> Unfortunately, the MDS continues to be a huge black box for me and the > >> locking code in particular is very tricky. I'd rather defer this for > >> anyone that is familiar with the code. > >> > >> Cheers, > >> -- > >> Luís > >> >
Hi! On Thu, Nov 28 2024, Alex Markuze wrote: > On Thu, Nov 28, 2024 at 7:43 PM Luis Henriques <luis.henriques@linux.dev> wrote: >> >> Hi Alex, >> >> [ Thank you for looking into this. ] >> >> On Wed, Nov 27 2024, Alex Markuze wrote: >> >> > Hi, Folks. >> > AFAIK there is no side effect that can affect MDS with this fix. >> > This crash happens following this patch >> > "1065da21e5df9d843d2c5165d5d576be000142a6" "ceph: stop copying to iter >> > at EOF on sync reads". >> > >> > Per your fix Luis, it seems to address only the cases when i_size goes >> > to zero but can happen anytime the `i_size` goes below `off`. >> > I propose fixing it this way: >> >> Hmm... you're probably right. I didn't see this happening, but I guess it >> could indeed happen. >> >> > diff --git a/fs/ceph/file.c b/fs/ceph/file.c >> > index 4b8d59ebda00..19b084212fee 100644 >> > --- a/fs/ceph/file.c >> > +++ b/fs/ceph/file.c >> > @@ -1066,7 +1066,7 @@ ssize_t __ceph_sync_read(struct inode *inode, >> > loff_t *ki_pos, >> > if (ceph_inode_is_shutdown(inode)) >> > return -EIO; >> > >> > - if (!len) >> > + if (!len || !i_size) >> > return 0; >> > /* >> > * flush any page cache pages in this range. this >> > @@ -1200,12 +1200,11 @@ ssize_t __ceph_sync_read(struct inode *inode, >> > loff_t *ki_pos, >> > } >> > >> > idx = 0; >> > - if (ret <= 0) >> > - left = 0; >> >> Right now I don't have any means for testing this patch. However, I don't >> think this is completely correct. By removing the above condition you're >> discarding cases where an error has occurred (i.e. where ret is negative). > > I didn't discard it though :). > I folded it into the `if` statement. I find the if else construct > overly verbose and cumbersome. > > + left = (ret > 0) ? ret : 0; > Right, but with your patch, if 'ret < 0', we could still hit the first branch instead of that one: if (off + ret > i_size) left = (i_size > off) ? i_size - off : 0; else left = (ret > 0) ? ret : 0; Cheers,
Good catch, I'm reworking the ergonomics of this function, this ret error code is checked and carried through the loop and checked every other line. On Thu, Nov 28, 2024 at 8:53 PM Luis Henriques <luis.henriques@linux.dev> wrote: > > Hi! > > On Thu, Nov 28 2024, Alex Markuze wrote: > > On Thu, Nov 28, 2024 at 7:43 PM Luis Henriques <luis.henriques@linux.dev> wrote: > >> > >> Hi Alex, > >> > >> [ Thank you for looking into this. ] > >> > >> On Wed, Nov 27 2024, Alex Markuze wrote: > >> > >> > Hi, Folks. > >> > AFAIK there is no side effect that can affect MDS with this fix. > >> > This crash happens following this patch > >> > "1065da21e5df9d843d2c5165d5d576be000142a6" "ceph: stop copying to iter > >> > at EOF on sync reads". > >> > > >> > Per your fix Luis, it seems to address only the cases when i_size goes > >> > to zero but can happen anytime the `i_size` goes below `off`. > >> > I propose fixing it this way: > >> > >> Hmm... you're probably right. I didn't see this happening, but I guess it > >> could indeed happen. > >> > >> > diff --git a/fs/ceph/file.c b/fs/ceph/file.c > >> > index 4b8d59ebda00..19b084212fee 100644 > >> > --- a/fs/ceph/file.c > >> > +++ b/fs/ceph/file.c > >> > @@ -1066,7 +1066,7 @@ ssize_t __ceph_sync_read(struct inode *inode, > >> > loff_t *ki_pos, > >> > if (ceph_inode_is_shutdown(inode)) > >> > return -EIO; > >> > > >> > - if (!len) > >> > + if (!len || !i_size) > >> > return 0; > >> > /* > >> > * flush any page cache pages in this range. this > >> > @@ -1200,12 +1200,11 @@ ssize_t __ceph_sync_read(struct inode *inode, > >> > loff_t *ki_pos, > >> > } > >> > > >> > idx = 0; > >> > - if (ret <= 0) > >> > - left = 0; > >> > >> Right now I don't have any means for testing this patch. However, I don't > >> think this is completely correct. By removing the above condition you're > >> discarding cases where an error has occurred (i.e. where ret is negative). > > > > I didn't discard it though :). > > I folded it into the `if` statement. I find the if else construct > > overly verbose and cumbersome. > > > > + left = (ret > 0) ? ret : 0; > > > > Right, but with your patch, if 'ret < 0', we could still hit the first > branch instead of that one: > > if (off + ret > i_size) > left = (i_size > off) ? i_size - off : 0; > else > left = (ret > 0) ? ret : 0; > > Cheers, > -- > Luís >
This patch does three things:
1. The allocated pages are bound to the request, simplifying the
memory management especially on the bad path.
2. ret is checked at the earliest point instead of being carried
through the loop.
3. The overflow bug is fixed.
diff --git a/fs/ceph/file.c b/fs/ceph/file.c
index 4b8d59ebda00..9522d5218c04 100644
--- a/fs/ceph/file.c
+++ b/fs/ceph/file.c
@@ -1066,7 +1066,7 @@ ssize_t __ceph_sync_read(struct inode *inode,
loff_t *ki_pos,
if (ceph_inode_is_shutdown(inode))
return -EIO;
- if (!len)
+ if (!len || !i_size)
return 0;
/*
* flush any page cache pages in this range. this
@@ -1086,7 +1086,7 @@ ssize_t __ceph_sync_read(struct inode *inode,
loff_t *ki_pos,
int num_pages;
size_t page_off;
bool more;
- int idx;
+ int idx = 0;
size_t left;
struct ceph_osd_req_op *op;
u64 read_off = off;
@@ -1127,7 +1127,7 @@ ssize_t __ceph_sync_read(struct inode *inode,
loff_t *ki_pos,
osd_req_op_extent_osd_data_pages(req, 0, pages, read_len,
offset_in_page(read_off),
- false, false);
+ false, true);
op = &req->r_ops[0];
if (sparse) {
@@ -1160,7 +1160,15 @@ ssize_t __ceph_sync_read(struct inode *inode,
loff_t *ki_pos,
else if (ret == -ENOENT)
ret = 0;
- if (ret > 0 && IS_ENCRYPTED(inode)) {
+ if (ret < 0) {
+ ceph_osdc_put_request(req);
+
+ if (ret == -EBLOCKLISTED)
+ fsc->blocklisted = true;
+ break;
+ }
+
+ if (IS_ENCRYPTED(inode)) {
int fret;
fret = ceph_fscrypt_decrypt_extents(inode, pages,
@@ -1186,10 +1194,8 @@ ssize_t __ceph_sync_read(struct inode *inode,
loff_t *ki_pos,
ret = min_t(ssize_t, fret, len);
}
- ceph_osdc_put_request(req);
-
/* Short read but not EOF? Zero out the remainder. */
- if (ret >= 0 && ret < len && (off + ret < i_size)) {
+ if (ret < len && (off + ret < i_size)) {
int zlen = min(len - ret, i_size - off - ret);
int zoff = page_off + ret;
@@ -1199,13 +1205,11 @@ ssize_t __ceph_sync_read(struct inode *inode,
loff_t *ki_pos,
ret += zlen;
}
- idx = 0;
- if (ret <= 0)
- left = 0;
- else if (off + ret > i_size)
- left = i_size - off;
+ if (off + ret > i_size)
+ left = (i_size > off) ? i_size - off : 0;
else
left = ret;
+
while (left > 0) {
size_t plen, copied;
@@ -1221,13 +1225,8 @@ ssize_t __ceph_sync_read(struct inode *inode,
loff_t *ki_pos,
break;
}
}
- ceph_release_page_vector(pages, num_pages);
- if (ret < 0) {
- if (ret == -EBLOCKLISTED)
- fsc->blocklisted = true;
- break;
- }
+ ceph_osdc_put_request(req);
if (off >= i_size || !more)
break;
On Thu, Nov 28, 2024 at 9:09 PM Alex Markuze <amarkuze@redhat.com> wrote:
>
> Good catch, I'm reworking the ergonomics of this function, this ret
> error code is checked and carried through the loop and checked every
> other line.
>
> On Thu, Nov 28, 2024 at 8:53 PM Luis Henriques <luis.henriques@linux.dev> wrote:
> >
> > Hi!
> >
> > On Thu, Nov 28 2024, Alex Markuze wrote:
> > > On Thu, Nov 28, 2024 at 7:43 PM Luis Henriques <luis.henriques@linux.dev> wrote:
> > >>
> > >> Hi Alex,
> > >>
> > >> [ Thank you for looking into this. ]
> > >>
> > >> On Wed, Nov 27 2024, Alex Markuze wrote:
> > >>
> > >> > Hi, Folks.
> > >> > AFAIK there is no side effect that can affect MDS with this fix.
> > >> > This crash happens following this patch
> > >> > "1065da21e5df9d843d2c5165d5d576be000142a6" "ceph: stop copying to iter
> > >> > at EOF on sync reads".
> > >> >
> > >> > Per your fix Luis, it seems to address only the cases when i_size goes
> > >> > to zero but can happen anytime the `i_size` goes below `off`.
> > >> > I propose fixing it this way:
> > >>
> > >> Hmm... you're probably right. I didn't see this happening, but I guess it
> > >> could indeed happen.
> > >>
> > >> > diff --git a/fs/ceph/file.c b/fs/ceph/file.c
> > >> > index 4b8d59ebda00..19b084212fee 100644
> > >> > --- a/fs/ceph/file.c
> > >> > +++ b/fs/ceph/file.c
> > >> > @@ -1066,7 +1066,7 @@ ssize_t __ceph_sync_read(struct inode *inode,
> > >> > loff_t *ki_pos,
> > >> > if (ceph_inode_is_shutdown(inode))
> > >> > return -EIO;
> > >> >
> > >> > - if (!len)
> > >> > + if (!len || !i_size)
> > >> > return 0;
> > >> > /*
> > >> > * flush any page cache pages in this range. this
> > >> > @@ -1200,12 +1200,11 @@ ssize_t __ceph_sync_read(struct inode *inode,
> > >> > loff_t *ki_pos,
> > >> > }
> > >> >
> > >> > idx = 0;
> > >> > - if (ret <= 0)
> > >> > - left = 0;
> > >>
> > >> Right now I don't have any means for testing this patch. However, I don't
> > >> think this is completely correct. By removing the above condition you're
> > >> discarding cases where an error has occurred (i.e. where ret is negative).
> > >
> > > I didn't discard it though :).
> > > I folded it into the `if` statement. I find the if else construct
> > > overly verbose and cumbersome.
> > >
> > > + left = (ret > 0) ? ret : 0;
> > >
> >
> > Right, but with your patch, if 'ret < 0', we could still hit the first
> > branch instead of that one:
> >
> > if (off + ret > i_size)
> > left = (i_size > off) ? i_size - off : 0;
> > else
> > left = (ret > 0) ? ret : 0;
> >
> > Cheers,
> > --
> > Luís
> >
diff --git a/fs/ceph/file.c b/fs/ceph/file.c index 4b8d59ebda00..41d4eac128bb 100644 --- a/fs/ceph/file.c +++ b/fs/ceph/file.c @@ -1066,7 +1066,7 @@ ssize_t __ceph_sync_read(struct inode *inode, loff_t *ki_pos, if (ceph_inode_is_shutdown(inode)) return -EIO; - if (!len) + if (!len || !i_size) return 0; /* * flush any page cache pages in this range. this @@ -1154,6 +1154,9 @@ ssize_t __ceph_sync_read(struct inode *inode, loff_t *ki_pos, doutc(cl, "%llu~%llu got %zd i_size %llu%s\n", off, len, ret, i_size, (more ? " MORE" : "")); + if (i_size == 0) + ret = 0; + /* Fix it to go to end of extent map */ if (sparse && ret >= 0) ret = ceph_sparse_ext_map_end(op);
__ceph_sync_read() does not correctly handle reads when the inode size is zero. It is easy to hit a NULL pointer dereference by continuously reading a file while, on another client, we keep truncating and writing new data into it. The NULL pointer dereference happens when the inode size is zero but the read op returns some data (ceph_osdc_wait_request()). This will lead to 'left' being set to a huge value due to the overflow in: left = i_size - off; and, in the loop that follows, the pages[] array being accessed beyond num_pages. This patch fixes the issue simply by checking the inode size and returning if it is zero, even if there was data from the read op. Link: https://tracker.ceph.com/issues/67524 Fixes: 1065da21e5df ("ceph: stop copying to iter at EOF on sync reads") Signed-off-by: Luis Henriques (SUSE) <luis.henriques@linux.dev> --- fs/ceph/file.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)