KASAN: use-after-free Read in erspan_xmit

[syzbot]

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+f14b37...@syzkaller.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 syzk...@googlegroups.com.

syzbot will keep track of this bug report.
If you forgot to add the Reported-by tag, once the fix for this bug is
merged
into any tree, please reply to this email with:
#syz fix: exact-commit-title
If you want to test a patch for this bug, please reply with:
#syz test: git://repo/address.git branch
and provide the patch inline or as an attachment.
To mark this as a duplicate of another syzbot report, please reply with:
#syz dup: exact-subject-of-another-report
If it's a one-off invalid bug report, please reply with:
#syz invalid
Note: if the crash happens again, it will cause creation of a new bug
report.
Note: all commands must start from beginning of the line in the email body.

[David Ahern]

[ cc William Tu ]