[PATCH] llc: Return -EINPROGRESS from llc_ui_connect()

[PATCH] llc: Return -EINPROGRESS from llc_ui_connect()

[Ernestas Kulik]

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.

Set rc to -EINPROGRESS before considering blocking, akin to AF_INET
sockets.

Signed-off-by: Ernestas Kulik <ernestas.k@iconn-networks.com>
---
 net/llc/af_llc.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/llc/af_llc.c b/net/llc/af_llc.c
index 59d593bb5d18..9317d092ba84 100644
--- a/net/llc/af_llc.c
+++ b/net/llc/af_llc.c
@@ -515,10 +515,12 @@ static int llc_ui_connect(struct socket *sock, struct sockaddr_unsized *uaddr,
 		sock->state  = SS_UNCONNECTED;
 		sk->sk_state = TCP_CLOSE;
 		goto out;
 	}
 
+	rc = -EINPROGRESS;
+
 	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))
 			goto out;
-- 
2.53.0

Re: [PATCH] llc: Return -EINPROGRESS from llc_ui_connect()

[Jakub Kicinski]

On Wed, 15 Apr 2026 09:34:57 +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.
> 
> Set rc to -EINPROGRESS before considering blocking, akin to AF_INET
> sockets.

Please add a note on how you discovered this issue.
Including whether you're actively using this code or just scanning it
for bugs.

> diff --git a/net/llc/af_llc.c b/net/llc/af_llc.c
> index 59d593bb5d18..9317d092ba84 100644
> --- a/net/llc/af_llc.c
> +++ b/net/llc/af_llc.c
> @@ -515,10 +515,12 @@ static int llc_ui_connect(struct socket *sock, struct sockaddr_unsized *uaddr,
>  		sock->state  = SS_UNCONNECTED;
>  		sk->sk_state = TCP_CLOSE;
>  		goto out;
>  	}
>  
> +	rc = -EINPROGRESS;

Isn't this a bit of an odd placement? ..

>  	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))
>  			goto out;

.. I suspect you mean to target this branch, right?

Re: [PATCH] llc: Return -EINPROGRESS from llc_ui_connect()

[Ernestas Kulik]

On 2026-04-20 21:41, Jakub Kicinski wrote:
> On Wed, 15 Apr 2026 09:34:57 +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.
>>
>> Set rc to -EINPROGRESS before considering blocking, akin to AF_INET
>> sockets.
> 
> Please add a note on how you discovered this issue.
> Including whether you're actively using this code or just scanning it
> for bugs.

Will do. It was discovered while adding support for AF_LLC sockets in 
libcoap, the usual code path for client connections was failing due to 
this specific issue, so I figured the behavior should be analogous to 
AF_INET.

>> diff --git a/net/llc/af_llc.c b/net/llc/af_llc.c
>> index 59d593bb5d18..9317d092ba84 100644
>> --- a/net/llc/af_llc.c
>> +++ b/net/llc/af_llc.c
>> @@ -515,10 +515,12 @@ static int llc_ui_connect(struct socket *sock, struct sockaddr_unsized *uaddr,
>>   		sock->state  = SS_UNCONNECTED;
>>   		sk->sk_state = TCP_CLOSE;
>>   		goto out;
>>   	}
>>   
>> +	rc = -EINPROGRESS;
> 
> Isn't this a bit of an odd placement? ..
> 
>>   	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))
>>   			goto out;
> 
> .. I suspect you mean to target this branch, right?

I can’t remember now why I put it there, but you’re right, that would be 
the better place.

[PATCH v2] llc: Return -EINPROGRESS from llc_ui_connect()

[Ernestas Kulik]

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 before considering blocking, akin to AF_INET
sockets.

Signed-off-by: Ernestas Kulik <ernestas.k@iconn-networks.com>
---
 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

[PATCH v3] llc: Return -EINPROGRESS from llc_ui_connect()

[Ernestas Kulik]

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