netdev - Re: net/l2tp:BUG: KASAN: use-after-free in l2tp_ip6

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Message-ID: <CAM_iQpWpf--gXPy7zD7ax4vt-foMCh_dw8Pbb3=y_gSgegeF3Q@mail.gmail.com>
Date:   Sun, 16 Oct 2016 12:50:31 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Baozeng Ding <sploving1@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: net/l2tp:BUG: KASAN: use-after-free in l2tp_ip6_close

On Sun, Oct 16, 2016 at 8:07 AM, Baozeng Ding <sploving1@...il.com> wrote:
> Hello,
> While running syzkaller fuzzer I have got the following use-after-free
> bug in l2tp_ip6_close. The kernel version is 4.8.0+ (on Oct 7 commit d1f5323370fceaed43a7ee38f4c7bfc7e70f28d0).
>
> BUG: KASAN: use-after-free in l2tp_ip6_close+0x22e/0x290 at addr ffff8800081b0ed8
> Write of size 8 by task syz-executor/10987
> CPU: 0 PID: 10987 Comm: syz-executor Not tainted 4.8.0+ #39
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.8.2-0-g33fbe13 by qemu-project.org 04/01/2014
>  ffff880031d97838 ffffffff829f835b ffff88001b5a1640 ffff8800081b0ec0
>  ffff8800081b15a0 ffff8800081b6d20 ffff880031d97860 ffffffff8174d3cc
>  ffff880031d978f0 ffff8800081b0e80 ffff88001b5a1640 ffff880031d978e0
> Call Trace:
>  [<ffffffff829f835b>] dump_stack+0xb3/0x118 lib/dump_stack.c:15
>  [<ffffffff8174d3cc>] kasan_object_err+0x1c/0x70 mm/kasan/report.c:156
>  [<     inline     >] print_address_description mm/kasan/report.c:194
>  [<ffffffff8174d666>] kasan_report_error+0x1f6/0x4d0 mm/kasan/report.c:283
>  [<     inline     >] kasan_report mm/kasan/report.c:303
>  [<ffffffff8174db7e>] __asan_report_store8_noabort+0x3e/0x40 mm/kasan/report.c:329
>  [<     inline     >] __write_once_size ./include/linux/compiler.h:249
>  [<     inline     >] __hlist_del ./include/linux/list.h:622
>  [<     inline     >] hlist_del_init ./include/linux/list.h:637
>  [<ffffffff8579047e>] l2tp_ip6_close+0x22e/0x290 net/l2tp/l2tp_ip6.c:239


This one looks pretty interesting, how the hell could we call ____fput() twice
on the same fd...


>  [<ffffffff850b2dfd>] inet_release+0xed/0x1c0 net/ipv4/af_inet.c:415
>  [<ffffffff851dc5a0>] inet6_release+0x50/0x70 net/ipv6/af_inet6.c:422
>  [<ffffffff84c4581d>] sock_release+0x8d/0x1d0 net/socket.c:570
>  [<ffffffff84c45976>] sock_close+0x16/0x20 net/socket.c:1017
>  [<ffffffff817a108c>] __fput+0x28c/0x780 fs/file_table.c:208
>  [<ffffffff817a1605>] ____fput+0x15/0x20 fs/file_table.c:244
>  [<ffffffff813774f9>] task_work_run+0xf9/0x170
>  [<ffffffff81324aae>] do_exit+0x85e/0x2a00
>  [<ffffffff81326dc8>] do_group_exit+0x108/0x330
>  [<ffffffff81348cf7>] get_signal+0x617/0x17a0 kernel/signal.c:2307
>  [<ffffffff811b49af>] do_signal+0x7f/0x18f0
>  [<ffffffff810039bf>] exit_to_usermode_loop+0xbf/0x150 arch/x86/entry/common.c:156
>  [<     inline     >] prepare_exit_to_usermode arch/x86/entry/common.c:190
>  [<ffffffff81006060>] syscall_return_slowpath+0x1a0/0x1e0 arch/x86/entry/common.c:259
>  [<ffffffff85e4d726>] entry_SYSCALL_64_fastpath+0xc4/0xc6
> Object at ffff8800081b0ec0, in cache L2TP/IPv6 size: 1448
> Allocated:
> PID = 10987
>  [ 1116.897025] [<ffffffff811ddcb6>] save_stack_trace+0x16/0x20
>  [ 1116.897025] [<ffffffff8174c736>] save_stack+0x46/0xd0
>  [ 1116.897025] [<ffffffff8174c9ad>] kasan_kmalloc+0xad/0xe0
>  [ 1116.897025] [<ffffffff8174cee2>] kasan_slab_alloc+0x12/0x20
>  [ 1116.897025] [<     inline     >] slab_post_alloc_hook mm/slab.h:417
>  [ 1116.897025] [<     inline     >] slab_alloc_node mm/slub.c:2708
>  [ 1116.897025] [<     inline     >] slab_alloc mm/slub.c:2716
>  [ 1116.897025] [<ffffffff817476a8>] kmem_cache_alloc+0xc8/0x2b0 mm/slub.c:2721
>  [ 1116.897025] [<ffffffff84c4f6a9>] sk_prot_alloc+0x69/0x2b0 net/core/sock.c:1326
>  [ 1116.897025] [<ffffffff84c58ac8>] sk_alloc+0x38/0xae0 net/core/sock.c:1388
>  [ 1116.897025] [<ffffffff851ddf67>] inet6_create+0x2d7/0x1000 net/ipv6/af_inet6.c:182
>  [ 1116.897025] [<ffffffff84c4af7b>] __sock_create+0x37b/0x640 net/socket.c:1153
>  [ 1116.897025] [<     inline     >] sock_create net/socket.c:1193
>  [ 1116.897025] [<     inline     >] SYSC_socket net/socket.c:1223
>  [ 1116.897025] [<ffffffff84c4b46f>] SyS_socket+0xef/0x1b0 net/socket.c:1203
>  [ 1116.897025] [<ffffffff85e4d685>] entry_SYSCALL_64_fastpath+0x23/0xc6
> Freed:
> PID = 10987
>  [ 1116.897025] [<ffffffff811ddcb6>] save_stack_trace+0x16/0x20
>  [ 1116.897025] [<ffffffff8174c736>] save_stack+0x46/0xd0
>  [ 1116.897025] [<ffffffff8174cf61>] kasan_slab_free+0x71/0xb0
>  [ 1116.897025] [<     inline     >] slab_free_hook mm/slub.c:1352
>  [ 1116.897025] [<     inline     >] slab_free_freelist_hook mm/slub.c:1374
>  [ 1116.897025] [<     inline     >] slab_free mm/slub.c:2951
>  [ 1116.897025] [<ffffffff81748b28>] kmem_cache_free+0xc8/0x330 mm/slub.c:2973
>  [ 1116.897025] [<     inline     >] sk_prot_free net/core/sock.c:1369
>  [ 1116.897025] [<ffffffff84c541eb>] __sk_destruct+0x32b/0x4f0 net/core/sock.c:1444
>  [ 1116.897025] [<ffffffff84c5aca4>] sk_destruct+0x44/0x80 net/core/sock.c:1452
>  [ 1116.897025] [<ffffffff84c5ad33>] __sk_free+0x53/0x220 net/core/sock.c:1460
>  [ 1116.897025] [<ffffffff84c5af23>] sk_free+0x23/0x30 net/core/sock.c:1471
>  [ 1116.897025] [<ffffffff84c5cb6c>] sk_common_release+0x28c/0x3e0 ./include/net/sock.h:1589
>  [ 1116.897025] [<ffffffff8579044e>] l2tp_ip6_close+0x1fe/0x290 net/l2tp/l2tp_ip6.c:243
>  [ 1116.897025] [<ffffffff850b2dfd>] inet_release+0xed/0x1c0 net/ipv4/af_inet.c:415
>  [ 1116.897025] [<ffffffff851dc5a0>] inet6_release+0x50/0x70 net/ipv6/af_inet6.c:422
>  [ 1116.897025] [<ffffffff84c4581d>] sock_release+0x8d/0x1d0 net/socket.c:570
>  [ 1116.897025] [<ffffffff84c45976>] sock_close+0x16/0x20 net/socket.c:1017
>  [ 1116.897025] [<ffffffff817a108c>] __fput+0x28c/0x780 fs/file_table.c:208
>  [ 1116.897025] [<ffffffff817a1605>] ____fput+0x15/0x20 fs/file_table.c:244
>  [ 1116.897025] [<ffffffff813774f9>] task_work_run+0xf9/0x170
>  [ 1116.897025] [<ffffffff81324aae>] do_exit+0x85e/0x2a00
>  [ 1116.897025] [<ffffffff81326dc8>] do_group_exit+0x108/0x330
>  [ 1116.897025] [<ffffffff81348cf7>] get_signal+0x617/0x17a0 kernel/signal.c:2307
>  [ 1116.897025] [<ffffffff811b49af>] do_signal+0x7f/0x18f0
>  [ 1116.897025] [<ffffffff810039bf>] exit_to_usermode_loop+0xbf/0x150 arch/x86/entry/common.c:156
>  [ 1116.897025] [<     inline     >] prepare_exit_to_usermode arch/x86/entry/common.c:190
>  [ 1116.897025] [<ffffffff81006060>] syscall_return_slowpath+0x1a0/0x1e0 arch/x86/entry/common.c:259
>  [ 1116.897025] [<ffffffff85e4d726>] entry_SYSCALL_64_fastpath+0xc4/0xc6
> Memory state around the buggy address:
>  ffff8800081b0d80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff8800081b0e00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>>ffff8800081b0e80: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
>                                                     ^
>  ffff8800081b0f00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8800081b0f80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
>
> Best Regards,
> Baozeng Ding