RE: [PATCH net] net/af_iucv: fix NULL deref in afiucv_hs_callback_syn()

[Jagielski, Jedrzej]

From: Hidayath Khan <hidayath@xxxxxxxxxxxxx> 
Sent: Thursday, July 9, 2026 9:18 PM

>afiucv_hs_callback_syn() allocates the child socket with GFP_ATOMIC.
>If the allocation fails, nsk is NULL.
>
>The connection-refused path is entered when the listen state check
>fails, the accept backlog is full, or nsk is NULL. The code
>unconditionally calls iucv_sock_kill(nsk) in that path.
>
>iucv_sock_kill() does not accept a NULL socket pointer and immediately
>dereferences sk via sock_flag(sk, SOCK_ZAPPED). When nsk is NULL,
>calling iucv_sock_kill(nsk) results in a NULL pointer dereference.
>
>Only call iucv_sock_kill() when a child socket was successfully
>allocated.
>
>Fixes: 3881ac441f64 ("af_iucv: add HiperSockets transport")
>Cc: stable@xxxxxxxxxxxxxxx
>Reviewed-by: Alexandra Winter <wintera@xxxxxxxxxxxxx>
>Signed-off-by: Hidayath Khan <hidayath@xxxxxxxxxxxxx>
>---
> net/iucv/af_iucv.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
>diff --git a/net/iucv/af_iucv.c b/net/iucv/af_iucv.c
>index fed240b453bd..f5b1ec44b6ae 100644
>--- a/net/iucv/af_iucv.c
>+++ b/net/iucv/af_iucv.c
>@@ -1872,7 +1872,8 @@ static int afiucv_hs_callback_syn(struct sock *sk, struct sk_buff *skb)
> 		afiucv_swap_src_dest(skb);
> 		trans_hdr->flags = AF_IUCV_FLAG_SYN | AF_IUCV_FLAG_FIN;
> 		err = dev_queue_xmit(skb);
>-		iucv_sock_kill(nsk);
>+		if (nsk)

Hi Hidayath

why not to move this check into iucv_sock_kill()?
would prevent from potential similar issues in the future

>+			iucv_sock_kill(nsk);
> 		bh_unlock_sock(sk);
> 		goto out;
> 	}
>
>base-commit: 262b2eac463d880a664cf92af1107b4f9d84ad37
>-- 
>2.52.0