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

[Hidayath Khan <hidayath@linux.ibm.com>]

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
-- 
2.52.0