Given a zero sk_sndtimeo, llc_ui_connect() skips waiting for state
change and returns 0, confusing userspace applications that will assume
the socket is connected, making e.g. getpeername() calls error out.

More specifically, the issue was discovered in libcoap, where
newly-added AF_LLC socket support was behaving differently from AF_INET
connections due to EINPROGRESS handling being skipped.

Set rc to -EINPROGRESS if connect() would not block, akin to AF_INET
sockets.

Signed-off-by: Ernestas Kulik <ernestas.k@iconn-networks.com>
---
v2:
- Add note about discovering the issue
- Make rc assignment conditional
v3:
- Fix commit message after v2 changes
---
 net/llc/af_llc.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/llc/af_llc.c b/net/llc/af_llc.c
index 59d593bb5d18..1b210db3119e 100644
--- a/net/llc/af_llc.c
+++ b/net/llc/af_llc.c
@@ -518,12 +518,14 @@ static int llc_ui_connect(struct socket *sock, struct sockaddr_unsized *uaddr,
 	}
 
 	if (sk->sk_state == TCP_SYN_SENT) {
 		const long timeo = sock_sndtimeo(sk, flags & O_NONBLOCK);
 
-		if (!timeo || !llc_ui_wait_for_conn(sk, timeo))
+		if (!timeo || !llc_ui_wait_for_conn(sk, timeo)) {
+			rc = -EINPROGRESS;
 			goto out;
+		}
 
 		rc = sock_intr_errno(timeo);
 		if (signal_pending(current))
 			goto out;
 	}
-- 
2.53.0

On Tue, Apr 21, 2026 at 09:02:26AM +0300, Ernestas Kulik wrote:
> Given a zero sk_sndtimeo, llc_ui_connect() skips waiting for state
> change and returns 0, confusing userspace applications that will assume
> the socket is connected, making e.g. getpeername() calls error out.
> 
> More specifically, the issue was discovered in libcoap, where
> newly-added AF_LLC socket support was behaving differently from AF_INET
> connections due to EINPROGRESS handling being skipped.
> 
> Set rc to -EINPROGRESS if connect() would not block, akin to AF_INET
> sockets.
> 
> Signed-off-by: Ernestas Kulik <ernestas.k@iconn-networks.com>
> ---
> v2:
> - Add note about discovering the issue
> - Make rc assignment conditional
> v3:
> - Fix commit message after v2 changes

Reviewed-by: Simon Horman <horms@kernel.org>