Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 5.1 086/155] nfsd: allow fh_want_write to be called twice | Date | Thu, 13 Jun 2019 10:33:18 +0200 |
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[ Upstream commit 0b8f62625dc309651d0efcb6a6247c933acd8b45 ]
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> --- fs/nfsd/vfs.h | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/fs/nfsd/vfs.h b/fs/nfsd/vfs.h index a7e107309f76..db351247892d 100644 --- a/fs/nfsd/vfs.h +++ b/fs/nfsd/vfs.h @@ -120,8 +120,11 @@ void nfsd_put_raparams(struct file *file, struct raparms *ra); static inline int fh_want_write(struct svc_fh *fh) { - int ret = mnt_want_write(fh->fh_export->ex_path.mnt); + int ret; + if (fh->fh_want_write) + return 0; + ret = mnt_want_write(fh->fh_export->ex_path.mnt); if (!ret) fh->fh_want_write = true; return ret; -- 2.20.1
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