Subject: KASAN: slab-out-of-bounds Read in erspan_xmit

From: syzbot <[email-masked]>
Date: Mon, 22 Jan 2018 11:58:04 -0800

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.

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Reported-by: [email-masked]
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==================================================================
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
==================================================================

---
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