Date:   Mon, 22 Jan 2018 15:45:22 -0700
From:   David Ahern <dsahern@...il.com>
To:     syzbot <syzbot+9723f2d288e49b492cf0@...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: slab-out-of-bounds 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 5 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+9723f2d288e49b492cf0@...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: slab-out-of-bounds in erspan_xmit+0x22d4/0x2430
> net/ipv4/ip_gre.c:735
> Read of size 2 at addr ffff8801c50bb08b by task syzkaller525754/3647
> 
> CPU: 0 PID: 3647 Comm: syzkaller525754 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: 0033:0x445649
> RSP: 002b:00007ffe82dde5b8 EFLAGS: 00000217 ORIG_RAX: 000000000000002c
> RAX: ffffffffffffffda RBX: ffffffffffffffff RCX: 0000000000445649
> RDX: 0000000000000000 RSI: 0000000020003fd9 RDI: 0000000000000004
> RBP: 00000000004a78c5 R08: 0000000020008000 R09: 000000000000001c
> R10: 0000000000000000 R11: 0000000000000217 R12: 0000000000402720
> R13: 00000000004027b0 R14: 0000000000000000 R15: 0000000000000000
> 
> Allocated by task 3221:
>  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
>  getname_flags+0xcb/0x580 fs/namei.c:138
>  getname+0x19/0x20 fs/namei.c:209
>  do_sys_open+0x2e7/0x6d0 fs/open.c:1053
>  SYSC_open fs/open.c:1077 [inline]
>  SyS_open+0x2d/0x40 fs/open.c:1072
>  entry_SYSCALL_64_fastpath+0x29/0xa0
> 
> Freed by task 3221:
>  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
>  putname+0xee/0x130 fs/namei.c:258
>  do_sys_open+0x31b/0x6d0 fs/open.c:1068
>  SYSC_open fs/open.c:1077 [inline]
>  SyS_open+0x2d/0x40 fs/open.c:1072
>  entry_SYSCALL_64_fastpath+0x29/0xa0
> 
> The buggy address belongs to the object at ffff8801c50ba000
>  which belongs to the cache names_cache of size 4096
> The buggy address is located 139 bytes to the right of
>  4096-byte region [ffff8801c50ba000, ffff8801c50bb000)
> The buggy address belongs to the page:
> page:ffffea0007142e80 count:1 mapcount:0 mapping:ffff8801c50ba000
> index:0x0 compound_mapcount: 0
> flags: 0x2fffc0000008100(slab|head)
> raw: 02fffc0000008100 ffff8801c50ba000 0000000000000000 0000000100000001
> raw: ffffea0007145320 ffffea00071433a0 ffff8801dae2c600 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>  ffff8801c50baf80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8801c50bb000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>> ffff8801c50bb080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>                       ^
>  ffff8801c50bb100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  ffff8801c50bb180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ==================================================================
> 
> 
> ---
> 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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