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author | J. Bruce Fields <bfields@redhat.com> | 2019-04-12 22:37:30 +0200 |
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committer | J. Bruce Fields <bfields@redhat.com> | 2019-04-24 15:46:35 +0200 |
commit | 0b8f62625dc309651d0efcb6a6247c933acd8b45 (patch) | |
tree | 3f059f6a586a7bcfeaed62896fdd50933aa1ddcb | |
parent | nfsd: knfsd must use the container user namespace (diff) | |
download | linux-0b8f62625dc309651d0efcb6a6247c933acd8b45.tar.xz linux-0b8f62625dc309651d0efcb6a6247c933acd8b45.zip |
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 <bfields@redhat.com>
-rw-r--r-- | fs/nfsd/vfs.h | 5 |
1 files changed, 4 insertions, 1 deletions
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; |