[PATCH 4.9 02/32] kcm: fix a null pointer dereference in kcm_sendmsg()

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: WANG Cong <xiyou.wangcong@xxxxxxxxx>


[ Upstream commit cd27b96bc13841ee7af25837a6ae86fee87273d6 ]

In commit 98e3862ca2b1 ("kcm: fix 0-length case for kcm_sendmsg()")
I tried to avoid skb allocation for 0-length case, but missed
a check for NULL pointer in the non EOR case.

Fixes: 98e3862ca2b1 ("kcm: fix 0-length case for kcm_sendmsg()")
Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Tom Herbert <tom@xxxxxxxxxxxxxxx>
Signed-off-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>
Acked-by: Tom Herbert <tom@xxxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/kcm/kcmsock.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -1044,8 +1044,10 @@ wait_for_memory:
 	} else {
 		/* Message not complete, save state */
 partial_message:
-		kcm->seq_skb = head;
-		kcm_tx_msg(head)->last_skb = skb;
+		if (head) {
+			kcm->seq_skb = head;
+			kcm_tx_msg(head)->last_skb = skb;
+		}
 	}
 
 	KCM_STATS_ADD(kcm->stats.tx_bytes, copied);