Re: net/icmp: null-ptr-deref in ping_v4_push_pending_frames

[Cong Wang]

On Mon, Feb 6, 2017 at 11:39 AM, Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote:
> Hi,
>
> I've got the following error report while running the syzkaller fuzzer.
>
> The null-ptr-deref is caused by sendto() on a socket(PF_INET,
> SOCK_DGRAM, PROT_ICMP).
> Note, that this requires the ability to create such sockets, which can
> be configured by net.ipv4.ping_group_range
> (https://lwn.net/Articles/422330/).
>
> A reproducer and .config are attached.
>
> On commit a572a1b999489efb591287632279c6c9eca3e4ed.
>
> 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
> RIP: 0033:0x445879
> RSP: 002b:00007f6f7c715b58 EFLAGS: 00000282 ORIG_RAX: 000000000000002c
> RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 0000000000445879
> RDX: 0000000000000008 RSI: 0000000020001000 RDI: 0000000000000005
> RBP: 00000000006e1ca0 R08: 0000000020ed9ff0 R09: 0000000000000010
> R10: 0000000020000010 R11: 0000000000000282 R12: 0000000000708000
> R13: 0000000000000000 R14: 00007f6f7c7169c0 R15: 00007f6f7c716700
> Code: 38 ca 7c 08 84 c9 0f 85 35 03 00 00 49 8d bf c2 00 00 00 66 89
> 83 a2 fe ff ff 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <0f>
> b6 14 02 48 89 f8 83 e0 07 83 c0 01 38 d0 7c 08 84 d2 0f 85
> RIP: ping_v4_push_pending_frames net/ipv4/ping.c:647 [inline] RSP:
> ffff880069bef8b8
> RIP: ping_v4_sendmsg+0x1acd/0x23f0 net/ipv4/ping.c:837 RSP: ffff880069bef8b8
> ---[ end trace 13dad24b243d08a7 ]---

This fixes it for me:

diff --git a/net/ipv4/ping.c b/net/ipv4/ping.c
index 86cca61..68d77b1 100644
--- a/net/ipv4/ping.c
+++ b/net/ipv4/ping.c
@@ -642,6 +642,8 @@ static int ping_v4_push_pending_frames(struct sock
*sk, struct pingfakehdr *pfh,
 {
        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);