module/sock: detect POLLHUP in is_connected with buffered data

When the peer closes a connection but unread data remains in the
receive buffer, recv(MSG_PEEK) returns > 0 and is_connected()
incorrectly reports true. Add poll(POLLHUP) check before
recv(MSG_PEEK) to detect peer hangup regardless of buffered data.

Fixes spdk#3842

Assisted-by: Cursor
Change-Id: Id5a835a6a3d1ceeac08e17ded2d442c300a176d2
Signed-off-by: Tomasz Zawadzki <tomasz.zawadzki@nutanix.com>
Reviewed-on: https://review.spdk.io/c/spdk/spdk/+/27957
Community-CI: Mellanox Build Bot
Tested-by: SPDK Automated Test System <spdkbot@gmail.com>
Reviewed-by: Jim Harris <jim.harris@nvidia.com>
Reviewed-by: Aleksey Marchuk <alexeymar@nvidia.com>

Author: tomzawadzki

module/sock/posix/posix.c

@@ -1768,11 +1768,19 @@ posix_sock_is_connected(struct spdk_sock *_sock)
 	struct spdk_posix_sock *sock = __posix_sock(_sock);
 	uint8_t byte;
 	int rc;
+	struct pollfd pfd;
 
 	if (posix_sock_is_connecting(sock)) {
 		return false;
 	}
 
+	pfd.fd = sock->fd;
+	pfd.events = 0;
+	pfd.revents = 0;
+	if (poll(&pfd, 1, 0) >= 0 && (pfd.revents & POLLHUP)) {
+		return false;
+	}
+
 	rc = recv(sock->fd, &byte, 1, MSG_PEEK);
 	if (rc == 0) {
 		return false;

module/sock/uring/uring.c

@@ -1501,6 +1501,14 @@ uring_sock_is_connected(struct spdk_sock *_sock)
 	struct spdk_uring_sock *sock = __uring_sock(_sock);
 	uint8_t byte;
 	int rc;
+	struct pollfd pfd;
+
+	pfd.fd = sock->fd;
+	pfd.events = 0;
+	pfd.revents = 0;
+	if (poll(&pfd, 1, 0) >= 0 && (pfd.revents & POLLHUP)) {
+		return false;
+	}
 
 	rc = recv(sock->fd, &byte, 1, MSG_PEEK | MSG_DONTWAIT);
 	if (rc == 0) {