kcm: fix a null pointer dereference in kcm_sendmsg()

[ 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@google.com>
Cc: Tom Herbert <tom@herbertland.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index 64f0e8531af0..a646f3481240 100644
--- 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);