Date:   Wed, 7 Jun 2017 10:43:41 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Gene Blue <geneblue.mail@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        James Morris <jmorris@...ei.org>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Patrick McHardy <kaber@...sh.net>,
        netdev <netdev@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: general protection fault in deactivate_slab

On Tue, Jun 6, 2017 at 4:24 AM, Andrey Konovalov <andreyknvl@...gle.com> wrote:
> On Tue, Jun 6, 2017 at 1:00 PM, Andrey Konovalov <andreyknvl@...gle.com> wrote:
>> On Tue, Jun 6, 2017 at 12:30 PM, Gene Blue <geneblue.mail@...il.com> wrote:
>>> Hi:
>>>   I got this crash when fuzzing the kernel with syzkaller.
>>>
>>>   My kernel version is  4.11.0-rc1 directly download from kernel.org.
>>>
>>>   And this crash is reproducible. Three times in total during the period of
>>> fuzzing.
>>
>> Hi!
>>
>> This has already been reported and fixed:
>> https://groups.google.com/forum/#!topic/syzkaller/e3I2c8X2oWo
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=232cd35d0804cc241eb887bb8d4d9b3b9881c64a
>
> Apparently I was wrong, this is actually a different bug, the stack
> trace just looks similar. I got the same report once on 4.12-rc3 which
> has "ipv6: fix out of bound writes in __ip6_append_data()".

But this one is IPv4. ;) We need a similar fix for IPv4 too, but it
is still _not_ related to this one which is inside slab allocator.

>
> kasan: GPF could be caused by NULL-ptr deref or user memory access
> general protection fault: 0000 [#1] SMP KASAN
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> Modules linked in:
> CPU: 1 PID: 32220 Comm: syz-executor6 Not tainted 4.12.0-rc3+ #3
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> task: ffff880037009700 task.stack: ffff880026ae0000
> RIP: 0010:get_freepointer mm/slub.c:243 [inline]
> RIP: 0010:deactivate_slab+0x63/0x5f0 mm/slub.c:2020
> RSP: 0018:ffff880026ae6f40 EFLAGS: 00010006
> RAX: 0000000000000000 RBX: ffffea0000e09400 RCX: 0000000000000000
> RDX: 00e906298e83888b RSI: ffffea0000e09400 RDI: ffff88003e80cf40
> RBP: ffff880026ae7000 R08: ffff880038253818 R09: ffff880038254018
> R10: ffff880026ae7020 R11: 0000000000000001 R12: 0000000000000000
> R13: 00e906298e83888b R14: ffff88003e80cf40 R15: ffff88003e80cf40
> FS:  00007f34fa033700(0000) GS:ffff88003ed00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f34fa032db8 CR3: 00000000388b2000 CR4: 00000000000006e0
> Call Trace:
>  ___slab_alloc+0x4f0/0x550 mm/slub.c:2595
>  __slab_alloc+0x51/0x90 mm/slub.c:2621
>  slab_alloc_node mm/slub.c:2684 [inline]
>  __kmalloc_node_track_caller+0x179/0x360 mm/slub.c:4303
>  __kmalloc_reserve.isra.32+0x46/0xe0 net/core/skbuff.c:138
>  __alloc_skb+0x15c/0x770 net/core/skbuff.c:231
>  alloc_skb include/linux/skbuff.h:936 [inline]
>  sock_wmalloc+0x156/0x1f0 net/core/sock.c:1879
>  __ip_append_data.isra.48+0x1e43/0x2d80 net/ipv4/ip_output.c:1041


I don't understand why we could cause NULL-ptr deref in slab allocator.
Is that slab overwritten by mistake already?


> bond0: bcsf0 ether type (3) is different from other slaves (1), can
> not enslave it
>  ip_append_data.part.49+0xe3/0x160 net/ipv4/ip_output.c:1235
>  ip_append_data+0x5f/0x80 net/ipv4/ip_output.c:1224
>  udp_sendmsg+0x10ae/0x2ce0 net/ipv4/udp.c:1073
>  inet_sendmsg+0x169/0x5c0 net/ipv4/af_inet.c:762
>  sock_sendmsg_nosec net/socket.c:633 [inline]
>  sock_sendmsg+0xcf/0x110 net/socket.c:643
>  ___sys_sendmsg+0x98a/0xa90 net/socket.c:1997
> bond0: bcsf0 ether type (3) is different from other slaves (1), can
> not enslave it
>  __sys_sendmsg+0x13d/0x320 net/socket.c:2031
> sctp: [Deprecated]: syz-executor7 (pid 32255) Use of struct
> sctp_assoc_value in delayed_ack socket option.
> Use struct sctp_sack_info instead
>  SYSC_sendmsg net/socket.c:2042 [inline]
>  SyS_sendmsg+0x32/0x50 net/socket.c:2038
> sctp: [Deprecated]: syz-executor7 (pid 32255) Use of struct
> sctp_assoc_value in delayed_ack socket option.
> Use struct sctp_sack_info instead
>  entry_SYSCALL_64_fastpath+0x1f/0xbe
> RIP: 0033:0x446179
> RSP: 002b:00007f34fa032c08 EFLAGS: 00000282 ORIG_RAX: 000000000000002e
> RAX: ffffffffffffffda RBX: 00000000000042a0 RCX: 0000000000446179
> RDX: 0000000000000800 RSI: 0000000020760000 RDI: 0000000000000005
> RBP: 00000000ffffffff R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000282 R12: 0000000000000005
> R13: 0000000000000000 R14: 00007f34fa0339c0 R15: 00007f34fa033700
> Code: 3a 48 8b 84 c7 d0 00 00 00 48 89 45 88 31 c0 4d 85 e4 0f 95 c0
> 83 c0 0f 48 85 d2 89 45 80 0f 84 7a 05 00 00 48 63 47 20 49 89 d5 <4c>
> 8b 34 02 4c 89 e2 4d 85 f6 0f 84 6b 05 00 00 48 8b 4b 18 49
> RIP: get_freepointer mm/slub.c:243 [inline] RSP: ffff880026ae6f40
> RIP: deactivate_slab+0x63/0x5f0 mm/slub.c:2020 RSP: ffff880026ae6f40
> sctp: [Deprecated]: syz-executor7 (pid 32258) Use of struct
> sctp_assoc_value in delayed_ack socket option.
> Use struct sctp_sack_info instead
> ---[ end trace 743c7af6619c952b ]---
> Kernel panic - not syncing: Fatal exception
> sctp: [Deprecated]: syz-executor7 (pid 32258) Use of struct
> sctp_assoc_value in delayed_ack socket option.
> Use struct sctp_sack_info instead
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> Kernel Offset: disabled
> Rebooting in 86400 seconds..
>
>

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