fuse: fix leaked notify reply

fuse_request_send_notify_reply() may fail if the connection was reset for
some reason (e.g. fs was unmounted).  Don't leak request reference in this
case.  Besides leaking memory, this resulted in fc->num_waiting not being
decremented and hence fuse_wait_aborted() left in a hanging and unkillable
state.

Fixes: 2d45ba381a ("fuse: add retrieve request")
Fixes: b8f95e5d13 ("fuse: umount should wait for all requests")
Reported-and-tested-by: syzbot+6339eda9cb4ebbc4c37b@syzkaller.appspotmail.com
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Cc: <stable@vger.kernel.org> #v2.6.36

fs/fuse/dev.c

@@ -1768,8 +1768,10 @@ static int fuse_retrieve(struct fuse_conn *fc, struct inode *inode,
 	req->in.args[1].size = total_len;
 
 	err = fuse_request_send_notify_reply(fc, req, outarg->notify_unique);
-	if (err)
+	if (err) {
 		fuse_retrieve_end(fc, req);
+		fuse_put_request(fc, req);
+	}
 
 	return err;
 }