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nfsd: allow fh_want_write to be called twice
[ Upstream commit 0b8f62625d
]
A fuzzer recently triggered lockdep warnings about potential sb_writers
deadlocks caused by fh_want_write().
Looks like we aren't careful to pair each fh_want_write() with an
fh_drop_write().
It's not normally a problem since fh_put() will call fh_drop_write() for
us. And was OK for NFSv3 where we'd do one operation that might call
fh_want_write(), and then put the filehandle.
But an NFSv4 protocol fuzzer can do weird things like call unlink twice
in a compound, and then we get into trouble.
I'm a little worried about this approach of just leaving everything to
fh_put(). But I think there are probably a lot of
fh_want_write()/fh_drop_write() imbalances so for now I think we need it
to be more forgiving.
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
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1 changed files with 4 additions and 1 deletions
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@ -116,8 +116,11 @@ void nfsd_put_raparams(struct file *file, struct raparms *ra);
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static inline int fh_want_write(struct svc_fh *fh)
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{
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int ret = mnt_want_write(fh->fh_export->ex_path.mnt);
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int ret;
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if (fh->fh_want_write)
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return 0;
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ret = mnt_want_write(fh->fh_export->ex_path.mnt);
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if (!ret)
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fh->fh_want_write = true;
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return ret;
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