fuse: prevent fuse_put_request on invalid pointer

fuse_direct_io() has a loop where requests are allocated in each
iteration. if allocation fails, the loop is broken out and follows
into an unconditional fuse_put_request() on that invalid pointer.
Signed-off-by: NAnand V. Avati <avati@gluster.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>
Cc: stable@kernel.org

fs/fuse/file.c

@@ -1063,7 +1063,8 @@ ssize_t fuse_direct_io(struct file *file, const char __user *buf,
 				break;
 		}
 	}
-	fuse_put_request(fc, req);
+	if (!IS_ERR(req))
+		fuse_put_request(fc, req);
 	if (res > 0)
 		*ppos = pos;