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

[Hidayathulla Khan I]

On 10/07/26 3:04 pm, Jagielski, Jedrzej wrote:
> 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
Hi Jedrzej,

Every other call to iucv_sock_kill() passes a non-NULL socket by 
construction.

If iucv_sock_kill() silently accepted NULL, a future caller wrongly
passing NULL would go unnoticed instead of being caught.

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