Date:   Mon, 22 Jan 2018 15:44:36 -0700
From:   David Ahern <dsahern@...il.com>
To:     syzbot <syzbot+f14b3703cd8d7670203f@...kaller.appspotmail.com>,
        davem@...emloft.net, kuznet@....inr.ac.ru,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, yoshfuji@...ux-ipv6.org,
        William Tu <u9012063@...il.com>
Subject: Re: KASAN: use-after-free Read in erspan_xmit

[ cc William Tu ]

On 1/22/18 12:58 PM, syzbot wrote:
> Hello,
> 
> syzbot hit the following crash on net-next commit
> 9d6474e458b13a94a0d5b141f2b8f38adf1991ae (Mon Jan 22 02:55:38 2018 +0000)
> tun: add missing rcu annotation
> 
> So far this crash happened 9 times on net-next.
> C reproducer is attached.
> syzkaller reproducer is attached.
> Raw console output is attached.
> compiler: gcc (GCC) 7.1.1 20170620
> .config is attached.
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+f14b3703cd8d7670203f@...kaller.appspotmail.com
> It will help syzbot understand when the bug is fixed. See footer for
> details.
> If you forward the report, please keep this part and the footer.
> 
> ==================================================================
> BUG: KASAN: use-after-free in erspan_xmit+0x22d4/0x2430
> net/ipv4/ip_gre.c:735
> Read of size 2 at addr ffff8801d890fa8b by task syzkaller099344/3658
> 
> CPU: 0 PID: 3658 Comm: syzkaller099344 Not tainted 4.15.0-rc8+ #203
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:17 [inline]
>  dump_stack+0x194/0x257 lib/dump_stack.c:53
>  print_address_description+0x73/0x250 mm/kasan/report.c:252
>  kasan_report_error mm/kasan/report.c:351 [inline]
>  kasan_report+0x25b/0x340 mm/kasan/report.c:409
>  __asan_report_load_n_noabort+0xf/0x20 mm/kasan/report.c:440
>  erspan_xmit+0x22d4/0x2430 net/ipv4/ip_gre.c:735
>  __netdev_start_xmit include/linux/netdevice.h:4053 [inline]
>  netdev_start_xmit include/linux/netdevice.h:4062 [inline]
>  packet_direct_xmit+0x3ad/0x790 net/packet/af_packet.c:267
>  packet_snd net/packet/af_packet.c:2944 [inline]
>  packet_sendmsg+0x3aed/0x60b0 net/packet/af_packet.c:2969
>  sock_sendmsg_nosec net/socket.c:630 [inline]
>  sock_sendmsg+0xca/0x110 net/socket.c:640
>  SYSC_sendto+0x361/0x5c0 net/socket.c:1721
>  SyS_sendto+0x40/0x50 net/socket.c:1689
>  entry_SYSCALL_64_fastpath+0x29/0xa0
> RIP: 0033:0x4455b9
> RSP: 002b:00007ffdea868098 EFLAGS: 00000217 ORIG_RAX: 000000000000002c
> RAX: ffffffffffffffda RBX: 0000000000000068 RCX: 00000000004455b9
> RDX: 0000000000000000 RSI: 0000000020003fd9 RDI: 0000000000000004
> RBP: 00000000004a7153 R08: 0000000020008000 R09: 000000000000001c
> R10: 0000000000000001 R11: 0000000000000217 R12: 00000000004026f0
> R13: 0000000000402780 R14: 0000000000000000 R15: 0000000000000000
> 
> Allocated by task 3727:
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:447
>  set_track mm/kasan/kasan.c:459 [inline]
>  kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:551
>  kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:489
>  kmem_cache_alloc+0x12e/0x760 mm/slab.c:3544
>  dup_mm kernel/fork.c:1187 [inline]
>  copy_mm+0x30a/0x131b kernel/fork.c:1250
>  copy_process.part.38+0x1ee9/0x4b20 kernel/fork.c:1752
>  copy_process kernel/fork.c:1565 [inline]
>  _do_fork+0x1f7/0xfe0 kernel/fork.c:2044
>  SYSC_clone kernel/fork.c:2154 [inline]
>  SyS_clone+0x37/0x50 kernel/fork.c:2148
>  do_syscall_64+0x273/0x920 arch/x86/entry/common.c:285
>  return_from_SYSCALL_64+0x0/0x75
> 
> Freed by task 3728:
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:447
>  set_track mm/kasan/kasan.c:459 [inline]
>  kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524
>  __cache_free mm/slab.c:3488 [inline]
>  kmem_cache_free+0x83/0x2a0 mm/slab.c:3746
>  __mmdrop+0x242/0x3d0 kernel/fork.c:911
>  mmdrop include/linux/sched/mm.h:43 [inline]
>  __mmput kernel/fork.c:933 [inline]
>  mmput+0x537/0x6d0 kernel/fork.c:944
>  exec_mmap fs/exec.c:1039 [inline]
>  flush_old_exec+0xc8b/0x2010 fs/exec.c:1271
>  load_elf_binary+0x87b/0x4c10 fs/binfmt_elf.c:864
>  search_binary_handler+0x142/0x6b0 fs/exec.c:1638
>  exec_binprm fs/exec.c:1680 [inline]
>  do_execveat_common.isra.30+0x1754/0x23c0 fs/exec.c:1802
>  do_execve fs/exec.c:1847 [inline]
>  SYSC_execve fs/exec.c:1928 [inline]
>  SyS_execve+0x39/0x50 fs/exec.c:1923
>  do_syscall_64+0x273/0x920 arch/x86/entry/common.c:285
>  return_from_SYSCALL_64+0x0/0x75
> 
> The buggy address belongs to the object at ffff8801d890f980
>  which belongs to the cache mm_struct of size 1440
> The buggy address is located 267 bytes inside of
>  1440-byte region [ffff8801d890f980, ffff8801d890ff20)
> The buggy address belongs to the page:
> page:ffffea0007624380 count:1 mapcount:0 mapping:ffff8801d890e080
> index:0x0 compound_mapcount: 0
> flags: 0x2fffc0000008100(slab|head)
> raw: 02fffc0000008100 ffff8801d890e080 0000000000000000 0000000100000005
> raw: ffffea0007629720 ffffea000763c5a0 ffff8801dae279c0 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>  ffff8801d890f980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8801d890fa00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>> ffff8801d890fa80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                       ^
>  ffff8801d890fb00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8801d890fb80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
> 
> 
> ---
> This bug is generated by a dumb bot. It may contain errors.
> See https://goo.gl/tpsmEJ for details.
> Direct all questions to syzkaller@...glegroups.com.
> 
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