Subject: Re: use-after-free in sctp_do_sm

From: Vlad Yasevich <[email-masked]>
Date: Wed, 25 Nov 2015 10:12:28 -0500

On 11/24/2015 03:45 PM, Neil Horman wrote:
> On Tue, Nov 24, 2015 at 11:10:32AM +0100, Dmitry Vyukov wrote:
>> On Tue, Nov 24, 2015 at 10:31 AM, Dmitry Vyukov <[email-masked]> wrote:
>>> On Tue, Nov 24, 2015 at 10:15 AM, Dmitry Vyukov <[email-masked]> wrote:
>>>> Hello,
>>>>
>>>> The following program triggers use-after-free in sctp_do_sm:
>>>>
>>>> // autogenerated by syzkaller (http://github.com/google/syzkaller)
>>>> #include <syscall.h>
>>>> #include <string.h>
>>>> #include <stdint.h>
>>>>
>>>> int main()
>>>> {
>>>>         long r0 = syscall(SYS_socket, 0xaul, 0x80805ul, 0x0ul, 0, 0, 0);
>>>>         long r1 = syscall(SYS_mmap, 0x20000000ul, 0x10000ul, 0x3ul,
>>>> 0x32ul, 0xfffffffffffffffful, 0x0ul);
>>>>         memcpy((void*)0x20002fe4,
>>>> "\x0a\x00\x33\xe7\xeb\x9d\xcf\x61\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\xc5\xc8\x88\x64",
>>>> 28);
>>>>         long r3 = syscall(SYS_bind, r0, 0x20002fe4ul, 0x1cul, 0, 0, 0);
>>>>         memcpy((void*)0x20000faa,
>>>> "\x9b\x01\x7d\xcd\xb8\x6a\xc7\x3d\x09\x3a\x07\x00\xa7\xc4\xe9\xee\x0a\xd6\xec\xde\x26\x75\x5f\x22\xae\x4e\x33\x00\xb0\x76\x10\x70\xd6\xca\x19\xbc\x15\x83\xcf\x2e\xbc\x99\x0c\x5e\x83\x89\xc1\x44\x9c\x6e\x74\xd8\x5d\x5d\xd0\xf0\xdf\x47\xc0\x00\x71\x0b\x55\x4c\xab\xf0\xd8\x90\xd5\x92\x8c\x6e\x33\x22\x15\x5b\x19\xfb\xed\xdd\xa6\xac\xcb\x60\xcf\xe2\xde\xed\xdb\x95\x5c\xaa\x20\xa3",
>>>> 94);
>>>>         memcpy((void*)0x2000033a,
>>>> "\x02\x00\x33\xe2\x7f\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00",
>>>> 128);
>>>>         long r6 = syscall(SYS_sendto, r0, 0x20000faaul, 0x5eul,
>>>> 0x81ul, 0x2000033aul, 0x80ul);
>>>>         return 0;
>>>> }
>>>>
>>>>
>>>> ==================================================================
>>>> BUG: KASAN: use-after-free in sctp_do_sm+0x42f6/0x4f60 at addr ffff880036fa80a8
>>>> Read of size 4 by task a.out/5664
>>>> =============================================================================
>>>> BUG kmalloc-4096 (Tainted: G    B          ): kasan: bad access detected
>>>> -----------------------------------------------------------------------------
>>>>
>>>> INFO: Allocated in sctp_association_new+0x6f/0x1ea0 age=8 cpu=1 pid=5664
>>>> [<      none      >] kmem_cache_alloc_trace+0x1cf/0x220 ./mm/slab.c:3707
>>>> [<      none      >] sctp_association_new+0x6f/0x1ea0
>>>> [<      none      >] sctp_sendmsg+0x1954/0x28e0
>>>> [<      none      >] inet_sendmsg+0x316/0x4f0 ./net/ipv4/af_inet.c:802
>>>> [<     inline     >] __sock_sendmsg_nosec ./net/socket.c:641
>>>> [<     inline     >] __sock_sendmsg ./net/socket.c:651
>>>> [<      none      >] sock_sendmsg+0xca/0x110 ./net/socket.c:662
>>>> [<      none      >] SYSC_sendto+0x208/0x350 ./net/socket.c:1841
>>>> [<      none      >] SyS_sendto+0x40/0x50 ./net/socket.c:1862
>>>> [<      none      >] entry_SYSCALL_64_fastpath+0x16/0x7a
>>>>
>>>> INFO: Freed in sctp_association_put+0x150/0x250 age=14 cpu=1 pid=5664
>>>> [<      none      >] kfree+0x199/0x1b0 ./mm/slab.c:1211
>>>> [<      none      >] sctp_association_put+0x150/0x250
>>>> [<      none      >] sctp_association_free+0x498/0x630
>>>> [<      none      >] sctp_do_sm+0xd8b/0x4f60
>>>> [<      none      >] sctp_primitive_SHUTDOWN+0xa9/0xd0
>>>> [<      none      >] sctp_close+0x616/0x790
>>>> [<      none      >] inet_release+0xed/0x1c0 ./net/ipv4/af_inet.c:471
>>>> [<      none      >] inet6_release+0x50/0x70 ./net/ipv6/af_inet6.c:416
>>>> [<     inline     >] constant_test_bit ././arch/x86/include/asm/bitops.h:321
>>>> [<      none      >] sock_release+0x8d/0x200 ./net/socket.c:601
>>>> [<      none      >] sock_close+0x16/0x20 ./net/socket.c:1188
>>>> [<      none      >] __fput+0x21d/0x6e0 ./fs/file_table.c:265
>>>> [<      none      >] ____fput+0x15/0x20 ./fs/file_table.c:84
>>>> [<      none      >] task_work_run+0x163/0x1f0 ./include/trace/events/rcu.h:20
>>>> [<     inline     >] __list_add ./include/linux/list.h:42
>>>> [<     inline     >] list_add_tail ./include/linux/list.h:76
>>>> [<     inline     >] list_move_tail ./include/linux/list.h:168
>>>> [<     inline     >] reparent_leader ./kernel/exit.c:618
>>>> [<     inline     >] forget_original_parent ./kernel/exit.c:669
>>>> [<     inline     >] exit_notify ./kernel/exit.c:697
>>>> [<      none      >] do_exit+0x809/0x2b90 ./kernel/exit.c:878
>>>> [<      none      >] do_group_exit+0x108/0x320 ./kernel/exit.c:985
>>>>
>>>> INFO: Slab 0xffffea0000dbea00 objects=7 used=1 fp=0xffff880036fa8000
>>>> flags=0x100000000004080
>>>> INFO: Object 0xffff880036fa8000 @offset=0 fp=0xffff880036fad668
>>>> CPU: 1 PID: 5664 Comm: a.out Tainted: G    B           4.4.0-rc1+ #81
>>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>>>>  00000000ffffffff ffff880061d6f700 ffffffff825d3336 ffff88003e806d00
>>>>  ffff880036fa8000 ffff880036fa8000 ffff880061d6f730 ffffffff81618784
>>>>  ffff88003e806d00 ffffea0000dbea00 ffff880036fa8000 0000000000000000
>>>>
>>>> Call Trace:
>>>>  [<ffffffff8162131e>] __asan_report_load4_noabort+0x3e/0x40
>>>>  [<ffffffff8475ac76>] sctp_do_sm+0x42f6/0x4f60
>>>>  [<ffffffff847b50e9>] sctp_primitive_SHUTDOWN+0xa9/0xd0
>>>>  [<ffffffff847a1426>] sctp_close+0x616/0x790
>>>>  [<ffffffff8409bb0d>] inet_release+0xed/0x1c0 ./net/ipv4/af_inet.c:471
>>>>  [<ffffffff84192cc0>] inet6_release+0x50/0x70 ./net/ipv6/af_inet6.c:416
>>>>  [<     inline     >] constant_test_bit ././arch/x86/include/asm/bitops.h:321
>>>>  [<ffffffff83dc78cd>] sock_release+0x8d/0x200 ./net/socket.c:601
>>>>  [<ffffffff83dc7a56>] sock_close+0x16/0x20 ./net/socket.c:1188
>>>>  [<ffffffff81662f5d>] __fput+0x21d/0x6e0 ./fs/file_table.c:265
>>>>  [<ffffffff816634a5>] ____fput+0x15/0x20 ./fs/file_table.c:84
>>>>  [<ffffffff812a33d3>] task_work_run+0x163/0x1f0 ./include/trace/events/rcu.h:20
>>>>  [<     inline     >] __list_add ./include/linux/list.h:42
>>>>  [<     inline     >] list_add_tail ./include/linux/list.h:76
>>>>  [<     inline     >] list_move_tail ./include/linux/list.h:168
>>>>  [<     inline     >] reparent_leader ./kernel/exit.c:618
>>>>  [<     inline     >] forget_original_parent ./kernel/exit.c:669
>>>>  [<     inline     >] exit_notify ./kernel/exit.c:697
>>>>  [<ffffffff812505d9>] do_exit+0x809/0x2b90 ./kernel/exit.c:878
>>>>  [<ffffffff81252ad8>] do_group_exit+0x108/0x320 ./kernel/exit.c:985
>>>>  [<ffffffff81252d0d>] SyS_exit_group+0x1d/0x20 ./kernel/exit.c:1002
>>>>  [<ffffffff84bf0c36>] entry_SYSCALL_64_fastpath+0x16/0x7a
>>>> ==================================================================
>>>>
>>>>
>>>> I am on commit 90b55590c43258a157a2a143748455dcc50fbb53 of net-next (Nov 22).
>>
>> The right commit is:
>>
>> commit 7d267278a9ece963d77eefec61630223fce08c6c
>> Author: Rainer Weikusat
>> Date:   Fri Nov 20 22:07:23 2015 +0000
>>     unix: avoid use-after-free in ep_remove_wait_queue
> This commit doesn't seem to exist

I don't think this matters...  I think what's happening is that a close is happening on a
socket still in connection initialization phase and we've never handled that particularly
well...

Net-next kernel with mem debugging hangs on boot for me with a ton of printks suppressed.
Will try the net kernel to see if that's better

-vlad
> 
> Neil
> 
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