io_uring: fix memory leak of UNIX domain socket inode

Opening and closing an io_uring instance leaks a UNIX domain socket
inode.  This is because the ->file of the io_uring instance's internal
UNIX domain socket is set to point to the io_uring file, but then
sock_release() sees the non-NULL ->file and assumes the inode reference
is held by the file so doesn't call iput().  That's not the case here,
since the reference is still meant to be held by the socket; the actual
inode of the io_uring file is different.

Fix this leak by NULL-ing out ->file before releasing the socket.

Reported-by: syzbot+111cb28d9f583693aefa@syzkaller.appspotmail.com
Fixes: 2b188cc1bb85 ("Add io_uring IO interface")
Cc: <stable@vger.kernel.org> # v5.1+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 0fbb486a320e927bb47aa1ac63fcea6ef6284760..86a2bd7219005b149f76b811117d5312ef8a63b8 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2777,8 +2777,10 @@ static void io_ring_ctx_free(struct io_ring_ctx *ctx)
        io_eventfd_unregister(ctx);
 
 #if defined(CONFIG_UNIX)
-       if (ctx->ring_sock)
+       if (ctx->ring_sock) {
+               ctx->ring_sock->file = NULL; /* so that iput() is called */
                sock_release(ctx->ring_sock);
+       }
 #endif
 
        io_mem_free(ctx->sq_ring);