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Subject[PATCH 3.2 141/199] ping: fix a null pointer dereference
3.2.87-rc1 review patch.  If anyone has any objections, please let me know.

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

From: WANG Cong <xiyou.wangcong@gmail.com>

commit 73d2c6678e6c3af7e7a42b1e78cd0211782ade32 upstream.

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.

Fixes: c319b4d76b9e ("net: ipv4: add IPPROTO_ICMP socket kind")
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Tested-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
net/ipv4/ping.c | 2 ++
1 file changed, 2 insertions(+)

--- a/net/ipv4/ping.c
+++ b/net/ipv4/ping.c
@@ -452,6 +452,8 @@ static int ping_push_pending_frames(stru
{
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);
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