nfsd: fix deadlock secinfo+readdir compound

commit 2f6fc056e899bd0144a08da5cacaecbe8997cd74 upstream.

nfsd_lookup_dentry exits with the parent filehandle locked.  fh_put also
unlocks if necessary (nfsd filehandle locking is probably too lenient),
so it gets unlocked eventually, but if the following op in the compound
needs to lock it again, we can deadlock.

A fuzzer ran into this; normal clients don't send a secinfo followed by
a readdir in the same compound.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index 5d3031ecb1dfd1dbb182ff98d2fabe4ba98a393e..5432605cce7d86dc7b94beef4d381737182e0538 100644 (file)
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -880,6 +880,7 @@ nfsd4_secinfo(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
                                    &exp, &dentry);
        if (err)
                return err;
+       fh_unlock(&cstate->current_fh);
        if (dentry->d_inode == NULL) {
                exp_put(exp);
                err = nfserr_noent;