From 0b8f62625dc309651d0efcb6a6247c933acd8b45 Mon Sep 17 00:00:00 2001 From: "J. Bruce Fields" Date: Fri, 12 Apr 2019 16:37:30 -0400 Subject: nfsd: allow fh_want_write to be called twice 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 --- fs/nfsd/vfs.h | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) (limited to 'fs/nfsd/vfs.h') 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; -- cgit v1.2.3-59-g8ed1b