* [PATCH] NFSD: memory corruption due to writing beyond the stat array
@ 2011-02-01 14:16 Konstantin Khorenko
2011-02-02 18:19 ` J. Bruce Fields
0 siblings, 1 reply; 2+ messages in thread
From: Konstantin Khorenko @ 2011-02-01 14:16 UTC (permalink / raw)
To: J. Bruce Fields, Neil Brown; +Cc: linux-nfs, Linux Kernel Mailing List
[-- Attachment #1: Type: text/plain, Size: 1419 bytes --]
Hi All,
i've found a bug which makes NFSD to corrupt memory due to writing beyond the stat array.
Initially this issue was found on 2.6.18-x RHEL5 kernel, but the same seems to be true for the current mainstream kernel (checked on 2.6.38-rc3).
./fs/nfsd/vfs.c:
static inline struct raparms *
nfsd_get_raparms(dev_t dev, ino_t ino)
{
...
// here we searched our file in a readahead cache
// but not found it
...
depth = nfsdstats.ra_size*11/10;
...
// some stuff, but "depth" is not changed
...
nfsdstats.ra_depth[depth*10/nfsdstats.ra_size]++;
...
}
And here we write to the 12th array element
(nfsdstats.ra_size*11/10*10/nfsdstats.ra_size == 11), while ra_depth has only
11 elements:
struct nfsd_stats {
...
unsigned int ra_depth[11]; /* number of times ra entry was found that deep
* in the cache (10percentiles). [10] = not found */
#ifdef CONFIG_NFSD_V4
unsigned int nfs4_opcount[LAST_NFS4_OP + 1]; /* count of individual
nfsv4 operations */
#endif
};
This means that each time we did not find a file in a readahead cache we
corrupt memory. Fortunately in a kernel with NFSDv4 compiled in it corrupts
(inc) NFS4 ops counter, but in a kernel with NFSDv4 disabled it corrupts (inc)
some other data, that lays in the memory beyond nfsdstats.
Proposed fix is attached.
--
Best regards,
Konstantin Khorenko
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NFSD: The patch fixes writing beyond the array.
If nfsd fails to find an exported via NFS file in the readahead cache,
it should increment corresponding nfsdstats counter (ra_depth[10]), but
due to a bug writes beside the stat array, corrupting following field.
In a kernel with NFSDv4 compiled in it corrupts (inc) NFS4 counter:
the number of individual nfsv4 operations.
In a kernel with NFSDv4 disabled it corrupts (inc) some other data,
that lays in the memory beyond nfsdstats.
Signed-off-by: Konstantin Khorenko <khorenko@openvz.org>
--- a/fs/nfsd/vfs.c.nfsd 2011-01-05 03:50:19.000000000 +0300
+++ b/fs/nfsd/vfs.c 2011-02-01 16:39:28.000000000 +0300
@@ -809,7 +809,7 @@ nfsd_get_raparms(dev_t dev, ino_t ino)
if (ra->p_count == 0)
frap = rap;
}
- depth = nfsdstats.ra_size*11/10;
+ depth = nfsdstats.ra_size;
if (!frap) {
spin_unlock(&rab->pb_lock);
return NULL;
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH] NFSD: memory corruption due to writing beyond the stat array
2011-02-01 14:16 [PATCH] NFSD: memory corruption due to writing beyond the stat array Konstantin Khorenko
@ 2011-02-02 18:19 ` J. Bruce Fields
0 siblings, 0 replies; 2+ messages in thread
From: J. Bruce Fields @ 2011-02-02 18:19 UTC (permalink / raw)
To: Konstantin Khorenko; +Cc: Neil Brown, linux-nfs, Linux Kernel Mailing List
On Tue, Feb 01, 2011 at 05:16:29PM +0300, Konstantin Khorenko wrote:
> Hi All,
>
> i've found a bug which makes NFSD to corrupt memory due to writing beyond the stat array.
>
> Initially this issue was found on 2.6.18-x RHEL5 kernel, but the same seems to be true for the current mainstream kernel (checked on 2.6.38-rc3).
>
> ./fs/nfsd/vfs.c:
> static inline struct raparms *
> nfsd_get_raparms(dev_t dev, ino_t ino)
> {
> ...
> // here we searched our file in a readahead cache
> // but not found it
> ...
> depth = nfsdstats.ra_size*11/10;
> ...
> // some stuff, but "depth" is not changed
> ...
> nfsdstats.ra_depth[depth*10/nfsdstats.ra_size]++;
> ...
> }
>
> And here we write to the 12th array element
> (nfsdstats.ra_size*11/10*10/nfsdstats.ra_size == 11),
Actually, I think that's true only if ra_size is divisible by 10; if
not, then depth will be something *less* than ra_size*11/10, so
depth*10/ra_size will be something less than 11 (namely 10).
> This means that each time we did not find a file in a readahead cache we
> corrupt memory.
... and ra_size is set to 16 * min(2, numthreads/8), so I think you'll
hit this only if min(2, numthreads/8) (rounded down) is a multiple of 5?
So for example someone using a number of threads that's a power of 2
shouldn't hit this case.
> Fortunately in a kernel with NFSDv4 compiled in it corrupts
> (inc) NFS4 ops counter, but in a kernel with NFSDv4 disabled it corrupts (inc)
> some other data, that lays in the memory beyond nfsdstats.
>
> Proposed fix is attached.
So after the fix:
> - depth = nfsdstats.ra_size*11/10;
> + depth = nfsdstats.ra_size;
depth*10/nfsdstats will always be 10 in this case. Looks good.
Thanks for finding this!
--b.
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2011-02-02 18:19 ` J. Bruce Fields
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