io_uring/net: ensure socket is marked connected on connect retry

io_uring does non-blocking connection attempts, which can yield some
unexpected results if a connect request is re-attempted by an an
application. This is equivalent to the following sync syscall sequence:

sock = socket(AF_INET, SOCK_STREAM | SOCK_NONBLOCK, IPPROTO_TCP);
connect(sock, &addr, sizeof(addr);

ret == -1 and errno == EINPROGRESS expected here. Now poll for POLLOUT
on sock, and when that returns, we expect the socket to be connected.
But if we follow that procedure with:

connect(sock, &addr, sizeof(addr));

you'd expect ret == -1 and errno == EISCONN here, but you actually get
ret == 0. If we attempt the connection one more time, then we get EISCON
as expected.

io_uring used to do this, but turns out that bluetooth fails with EBADFD
if you attempt to re-connect. Also looks like EISCONN _could_ occur with
this sequence.

Retain the ->in_progress logic, but work-around a potential EISCONN or
EBADFD error and only in those cases look at the sock_error(). This
should work in general and avoid the odd sequence of a repeated connect
request returning success when the socket is already connected.

This is all a side effect of the socket state being in a CONNECTING
state when we get EINPROGRESS, and only a re-connect or other related
operation will turn that into CONNECTED.

Cc: stable@vger.kernel.org
Fixes: 3fb1bd6 ("io_uring/net: handle -EINPROGRESS correct for IORING_OP_CONNECT")
Link: axboe/liburing#980
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: axboe

io_uring/net.c

@@ -1461,16 +1461,6 @@ int io_connect(struct io_kiocb *req, unsigned int issue_flags)
 	int ret;
 	bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK;
 
-	if (connect->in_progress) {
-		struct socket *socket;
-
-		ret = -ENOTSOCK;
-		socket = sock_from_file(req->file);
-		if (socket)
-			ret = sock_error(socket->sk);
-		goto out;
-	}
-
 	if (req_has_async_data(req)) {
 		io = req->async_data;
 	} else {
@@ -1490,9 +1480,7 @@ int io_connect(struct io_kiocb *req, unsigned int issue_flags)
 	    && force_nonblock) {
 		if (ret == -EINPROGRESS) {
 			connect->in_progress = true;
-			return -EAGAIN;
-		}
-		if (ret == -ECONNABORTED) {
+		} else if (ret == -ECONNABORTED) {
 			if (connect->seen_econnaborted)
 				goto out;
 			connect->seen_econnaborted = true;
@@ -1506,6 +1494,16 @@ int io_connect(struct io_kiocb *req, unsigned int issue_flags)
 		memcpy(req->async_data, &__io, sizeof(__io));
 		return -EAGAIN;
 	}
+	if (connect->in_progress) {
+		/*
+		 * At least bluetooth will return -EBADFD on a re-connect
+		 * attempt, and it's (supposedly) also valid to get -EISCONN
+		 * which means the previous result is good. For both of these,
+		 * grab the sock_error() and use that for the completion.
+		 */
+		if (ret == -EBADFD || ret == -EISCONN)
+			ret = sock_error(sock_from_file(req->file)->sk);
+	}
 	if (ret == -ERESTARTSYS)
 		ret = -EINTR;
 out: