KASAN: use-after-free Read in erspan_build_header

[syzbot]

Hello,

syzbot hit the following crash on upstream commit
0d665e7b109d512b7cae3ccef6e8654714887844 (Fri Jan 19 12:49:24 2018 +0000)
mm, page_vma_mapped: Drop faulty pointer arithmetics in check_pte()

So far this crash happened 11 times on upstream.
C reproducer is attached.
syzkaller reproducer is attached.
Raw console output is attached.
compiler: gcc (GCC) 7.1.1 20170620
.config is attached.
user-space arch: i386

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audit: type=1400 audit(1516645172.960:10): avc: denied { sys_chroot }
for pid=3651 comm="syzkaller942389" capability=18
scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023
tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=cap_userns
permissive=1
==================================================================
BUG: KASAN: use-after-free in erspan_build_header+0x3bf/0x3d0
net/ipv4/ip_gre.c:698
Read of size 2 at addr ffff8801d82a834b by task syzkaller942389/3651

CPU: 0 PID: 3651 Comm: syzkaller942389 Not tainted 4.15.0-rc9+ #184
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_build_header+0x3bf/0x3d0 net/ipv4/ip_gre.c:698
erspan_xmit+0x3b8/0x13b0 net/ipv4/ip_gre.c:740
__netdev_start_xmit include/linux/netdevice.h:4042 [inline]
netdev_start_xmit include/linux/netdevice.h:4051 [inline]
packet_direct_xmit+0x315/0x6b0 net/packet/af_packet.c:266
packet_snd net/packet/af_packet.c:2943 [inline]
packet_sendmsg+0x3aed/0x60b0 net/packet/af_packet.c:2968
sock_sendmsg_nosec net/socket.c:638 [inline]
sock_sendmsg+0xca/0x110 net/socket.c:648
SYSC_sendto+0x361/0x5c0 net/socket.c:1729
SyS_sendto+0x40/0x50 net/socket.c:1697
do_syscall_32_irqs_on arch/x86/entry/common.c:327 [inline]
do_fast_syscall_32+0x3ee/0xf9d arch/x86/entry/common.c:389
entry_SYSENTER_compat+0x54/0x63 arch/x86/entry/entry_64_compat.S:129
RIP: 0023:0xf7f0bc79
RSP: 002b:000000000820fdfc EFLAGS: 00000216 ORIG_RAX: 0000000000000171
RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 0000000020003fd9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000020008000
RBP: 000000000000001c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 3767:
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
prepare_creds+0x78/0x360 kernel/cred.c:252
SYSC_faccessat fs/open.c:365 [inline]
SyS_faccessat fs/open.c:353 [inline]
SYSC_access fs/open.c:431 [inline]
SyS_access+0x8f/0x6a0 fs/open.c:429
entry_SYSCALL_64_fastpath+0x29/0xa0

Freed by task 3768:
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
put_cred_rcu+0x263/0x400 kernel/cred.c:126
__rcu_reclaim kernel/rcu/rcu.h:195 [inline]
rcu_do_batch kernel/rcu/tree.c:2758 [inline]
invoke_rcu_callbacks kernel/rcu/tree.c:3012 [inline]
__rcu_process_callbacks kernel/rcu/tree.c:2979 [inline]
rcu_process_callbacks+0xd6c/0x17f0 kernel/rcu/tree.c:2996
__do_softirq+0x2d7/0xb85 kernel/softirq.c:285

The buggy address belongs to the object at ffff8801d82a8300
which belongs to the cache cred_jar of size 168
The buggy address is located 75 bytes inside of
168-byte region [ffff8801d82a8300, ffff8801d82a83a8)
The buggy address belongs to the page:
page:ffffea000760aa00 count:1 mapcount:0 mapping:ffff8801d82a8000 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801d82a8000 0000000000000000 0000000100000010
raw: ffffea00076115a0 ffffea00076138a0 ffff8801dad30380 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801d82a8200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801d82a8280: fb fb fb fb fb fc fc fc fc fc fc fc fc fc fc fc
> ffff8801d82a8300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8801d82a8380: fb fb fb fb fb fc fc fc fc fc fc fc fc fc fc fc
ffff8801d82a8400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
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[ cc William Tu]