linux-kernel - Re: net/kcm: GPF in kcm

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Message-ID: <CAM_iQpUAz+CNEJ=L=H5=_6WmcrD+Rsa9ZO3XPwVkp4kCjXGkSw@mail.gmail.com>
Date:   Mon, 13 Feb 2017 09:06:44 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     David Miller <davem@...emloft.net>,
        Tom Herbert <tom@...bertland.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Daniel Borkmann <daniel@...earbox.net>,
        Eric Dumazet <edumazet@...gle.com>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: net/kcm: GPF in kcm_sendmsg

On Mon, Feb 13, 2017 at 7:14 AM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> Hello,
>
> The following program triggers GPF in kcm_sendmsg:
>
>
> // autogenerated by syzkaller (http://github.com/google/syzkaller)
> #define _GNU_SOURCE
> #include <sys/socket.h>
> #include <sys/types.h>
> #include <sys/stat.h>
> #include <stddef.h>
> #include <string.h>
> #include <unistd.h>
>
> int main()
> {
>   int sock = socket(41 /*AF_KCM*/, SOCK_SEQPACKET, 0);
>   struct mmsghdr msg;
>   memset(&msg, 0, sizeof(msg));
>   sendmmsg(sock, &msg, 1, 0);
>   return 0;
> }
>
>
> general protection fault: 0000 [#1] SMP KASAN
> Modules linked in:
> CPU: 2 PID: 2935 Comm: a.out Not tainted 4.10.0-rc8+ #218
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> task: ffff88006b506440 task.stack: ffff8800662b8000
> RIP: 0010:kcm_sendmsg+0x92e/0x2240 net/kcm/kcmsock.c:1048

Hmm, head is NULL in kcm_tx_msg(head)->last_skb = skb;,
I missed the !eor case in the previous fix.


> RSP: 0018:ffff8800662bf720 EFLAGS: 00010202
> RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
> RDX: 0000000000000008 RSI: ffff88006b506c38 RDI: 0000000000000040
> RBP: ffff8800662bfa00 R08: 0000000000000001 R09: 0000000000000000
> R10: 0000000000000006 R11: 0000000000000000 R12: 7fffffffffffffff
> R13: dffffc0000000000 R14: 0000000000000000 R15: ffff88006af12040
> FS:  0000000001077880(0000) GS:ffff88006d100000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000004b2140 CR3: 00000000651b7000 CR4: 00000000001406e0
> Call Trace:
>  sock_sendmsg_nosec net/socket.c:635 [inline]
>  sock_sendmsg+0xca/0x110 net/socket.c:645
>  ___sys_sendmsg+0x4a3/0x9f0 net/socket.c:1985
>  __sys_sendmmsg+0x25c/0x750 net/socket.c:2075
>  SYSC_sendmmsg net/socket.c:2106 [inline]
>  SyS_sendmmsg+0x35/0x60 net/socket.c:2101
>  entry_SYSCALL_64_fastpath+0x1f/0xc2
> RIP: 0033:0x436dc9
> RSP: 002b:00007ffe84e1a938 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
> RAX: ffffffffffffffda RBX: 0000000000401730 RCX: 0000000000436dc9
> RDX: 0000000000000001 RSI: 00007ffe84e1a950 RDI: 0000000000000003
> RBP: 0000000000000000 R08: 000000000000000b R09: 0000000000000004
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000004002b0
> R13: 00007ffe84e1aa88 R14: 0000000000000002 R15: 0000000000000000
> Code: 02 00 0f 85 d4 14 00 00 48 8b 85 c0 fd ff ff 48 8d 78 40 49 89
> 87 30 05 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80>
> 3c 02 00 0f 85 9d 14 00 00 48 8b 85 c0 fd ff ff 4c 89 70 40
> RIP: kcm_sendmsg+0x92e/0x2240 net/kcm/kcmsock.c:1048 RSP: ffff8800662bf720
> ---[ end trace 62093774c8609871 ]---
>
>
> On commit 7089db84e356562f8ba737c29e472cc42d530dbc (4.10-rc8).