[ 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 0bf9e7bf5800..9140b9cf3870 100644 --- a/fs/nfsd/vfs.h +++ b/fs/nfsd/vfs.h @@ -116,8 +116,11 @@ 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;