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

[Paolo Abeni <pabeni@redhat.com>]

On 7/21/26 3:54 PM, Alexandra Winter wrote:
> On 09.07.26 21:17, Hidayath Khan wrote:
>> 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@vger.kernel.org
>> Reviewed-by: Alexandra Winter <wintera@linux.ibm.com>
>> Signed-off-by: Hidayath Khan <hidayath@linux.ibm.com>
>> ---
>>  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)
>> +			iucv_sock_kill(nsk);
>>  		bh_unlock_sock(sk);
>>  		goto out;
>>  	}
>>
>> base-commit: 262b2eac463d880a664cf92af1107b4f9d84ad37
> 
> 
> Gentle ping to netdev maintainers:
> Did this one get lost in the overflow?
> It is all green in patchwork. Is there something you need us to do?
> Should we re-send it?
> I don't see this as urgent or especially dangerous.
It's still alive in PW. Our backlog is unusually huge due to an
unfortunate sequence of season holidays and conferences, but hopefully
it should get back to normality someday in the future :)

/P