Patch "ping: fix a null pointer dereference" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

ping: fix a null pointer dereference

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
ping-fix-a-null-pointer-dereference.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: WANG Cong <[email protected]>
Date: Tue, 7 Feb 2017 12:59:46 -0800
Subject: ping: fix a null pointer dereference

From: WANG Cong <[email protected]>

[ Upstream commit 73d2c6678e6c3af7e7a42b1e78cd0211782ade32 ]

Andrey reported a kernel crash:

  general protection fault: 0000 [#1] SMP KASAN
  Dumping ftrace buffer:
     (ftrace buffer empty)
  Modules linked in:
  CPU: 2 PID: 3880 Comm: syz-executor1 Not tainted 4.10.0-rc6+ #124
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
  task: ffff880060048040 task.stack: ffff880069be8000
  RIP: 0010:ping_v4_push_pending_frames net/ipv4/ping.c:647 [inline]
  RIP: 0010:ping_v4_sendmsg+0x1acd/0x23f0 net/ipv4/ping.c:837
  RSP: 0018:ffff880069bef8b8 EFLAGS: 00010206
  RAX: dffffc0000000000 RBX: ffff880069befb90 RCX: 0000000000000000
  RDX: 0000000000000018 RSI: ffff880069befa30 RDI: 00000000000000c2
  RBP: ffff880069befbb8 R08: 0000000000000008 R09: 0000000000000000
  R10: 0000000000000002 R11: 0000000000000000 R12: ffff880069befab0
  R13: ffff88006c624a80 R14: ffff880069befa70 R15: 0000000000000000
  FS:  00007f6f7c716700(0000) GS:ffff88006de00000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 00000000004a6f28 CR3: 000000003a134000 CR4: 00000000000006e0
  Call Trace:
   inet_sendmsg+0x164/0x5b0 net/ipv4/af_inet.c:744
   sock_sendmsg_nosec net/socket.c:635 [inline]
   sock_sendmsg+0xca/0x110 net/socket.c:645
   SYSC_sendto+0x660/0x810 net/socket.c:1687
   SyS_sendto+0x40/0x50 net/socket.c:1655
   entry_SYSCALL_64_fastpath+0x1f/0xc2

This is because we miss a check for NULL pointer for skb_peek() when the queue is empty. Other places already have the same check.

---
 net/ipv4/ping.c |    2 ++
 1 file changed, 2 insertions(+)

@@ -642,6 +642,8 @@ static int ping_v4_push_pending_frames(s
 {
 	struct sk_buff *skb = skb_peek(&sk->sk_write_queue);
 
+	if (!skb)
+		return 0;
 	pfh->wcheck = csum_partial((char *)&pfh->icmph,
 		sizeof(struct icmphdr), pfh->wcheck);
 	pfh->icmph.checksum = csum_fold(pfh->wcheck);

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/sit-fix-a-double-free-on-error-path.patch queue-4.9/ping-fix-a-null-pointer-dereference.patch queue-4.9/net-use-a-work-queue-to-defer-net_disable_timestamp-work.patch