KASAN: slab-out-of-bounds Read in __xfrm_decode_session

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: cbafe18c Merge branch 'akpm' (patches from Andrew)
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12f20ca3600000
kernel config: https://syzkaller.appspot.com/x/.config?x=cb5c74e7f328d20b
dashboard link: https://syzkaller.appspot.com/bug?extid=6883e878b7a8f2efeeb2
compiler: gcc (GCC) 9.0.0 20181231 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+6883e8...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in decode_session6
net/xfrm/xfrm_policy.c:3390 [inline]
BUG: KASAN: slab-out-of-bounds in __xfrm_decode_session+0x1cfb/0x2e90
net/xfrm/xfrm_policy.c:3482
Read of size 1 at addr ffff8880915d1b49 by task kworker/0:0/16350

CPU: 0 PID: 16350 Comm: kworker/0:0 Not tainted 5.3.0+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Workqueue: events rt6_probe_deferred
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x172/0x1f0 lib/dump_stack.c:113
print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
__kasan_report.cold+0x1b/0x41 mm/kasan/report.c:506
kasan_report+0x12/0x20 mm/kasan/common.c:634
__asan_report_load1_noabort+0x14/0x20 mm/kasan/generic_report.c:129
decode_session6 net/xfrm/xfrm_policy.c:3390 [inline]
__xfrm_decode_session+0x1cfb/0x2e90 net/xfrm/xfrm_policy.c:3482
xfrm_decode_session include/net/xfrm.h:1137 [inline]
vti_tunnel_xmit+0x277/0x17a0 net/ipv4/ip_vti.c:269
__netdev_start_xmit include/linux/netdevice.h:4420 [inline]
netdev_start_xmit include/linux/netdevice.h:4434 [inline]
xmit_one net/core/dev.c:3280 [inline]
dev_hard_start_xmit+0x1a3/0x9b0 net/core/dev.c:3296
sch_direct_xmit+0x372/0xc30 net/sched/sch_generic.c:313
qdisc_restart net/sched/sch_generic.c:376 [inline]
__qdisc_run+0x577/0x1a00 net/sched/sch_generic.c:384
__dev_xmit_skb net/core/dev.c:3537 [inline]
__dev_queue_xmit+0x169d/0x3720 net/core/dev.c:3842
dev_queue_xmit+0x18/0x20 net/core/dev.c:3906
neigh_direct_output+0x16/0x20 net/core/neighbour.c:1530
neigh_output include/net/neighbour.h:511 [inline]
ip6_finish_output2+0x1034/0x2550 net/ipv6/ip6_output.c:116
__ip6_finish_output+0x444/0xaa0 net/ipv6/ip6_output.c:142
ip6_finish_output+0x38/0x1f0 net/ipv6/ip6_output.c:152
NF_HOOK_COND include/linux/netfilter.h:294 [inline]
ip6_output+0x235/0x7f0 net/ipv6/ip6_output.c:175
dst_output include/net/dst.h:436 [inline]
NF_HOOK include/linux/netfilter.h:305 [inline]
ndisc_send_skb+0xf29/0x14a0 net/ipv6/ndisc.c:505
ndisc_send_ns+0x3a9/0x850 net/ipv6/ndisc.c:647
rt6_probe_deferred+0xe3/0x1a0 net/ipv6/route.c:615
process_one_work+0x9af/0x1740 kernel/workqueue.c:2269
worker_thread+0x98/0xe40 kernel/workqueue.c:2415
kthread+0x361/0x430 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Allocated by task 3892:
save_stack+0x23/0x90 mm/kasan/common.c:69
set_track mm/kasan/common.c:77 [inline]
__kasan_kmalloc mm/kasan/common.c:510 [inline]
__kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:483
kasan_kmalloc+0x9/0x10 mm/kasan/common.c:524
__do_kmalloc mm/slab.c:3655 [inline]
__kmalloc+0x163/0x770 mm/slab.c:3664
kmalloc include/linux/slab.h:557 [inline]
tomoyo_realpath_from_path+0xcd/0x7b0 security/tomoyo/realpath.c:277
tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
tomoyo_path_number_perm+0x1dd/0x520 security/tomoyo/file.c:723
tomoyo_file_ioctl+0x23/0x30 security/tomoyo/tomoyo.c:335
security_file_ioctl+0x77/0xc0 security/security.c:1375
ksys_ioctl+0x57/0xd0 fs/ioctl.c:711
__do_sys_ioctl fs/ioctl.c:720 [inline]
__se_sys_ioctl fs/ioctl.c:718 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 3892:
save_stack+0x23/0x90 mm/kasan/common.c:69
set_track mm/kasan/common.c:77 [inline]
kasan_set_free_info mm/kasan/common.c:332 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/common.c:471
kasan_slab_free+0xe/0x10 mm/kasan/common.c:480
__cache_free mm/slab.c:3425 [inline]
kfree+0x10a/0x2c0 mm/slab.c:3756
tomoyo_realpath_from_path+0x1de/0x7b0 security/tomoyo/realpath.c:319
tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
tomoyo_path_number_perm+0x1dd/0x520 security/tomoyo/file.c:723
tomoyo_file_ioctl+0x23/0x30 security/tomoyo/tomoyo.c:335
security_file_ioctl+0x77/0xc0 security/security.c:1375
ksys_ioctl+0x57/0xd0 fs/ioctl.c:711
__do_sys_ioctl fs/ioctl.c:720 [inline]
__se_sys_ioctl fs/ioctl.c:718 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8880915d0680
which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 1225 bytes to the right of
4096-byte region [ffff8880915d0680, ffff8880915d1680)
The buggy address belongs to the page:
page:ffffea0002457400 refcount:1 mapcount:0 mapping:ffff8880aa402000
index:0x0 compound_mapcount: 0
flags: 0x1fffc0000010200(slab|head)
raw: 01fffc0000010200 ffffea0000d97208 ffffea00025a7b88 ffff8880aa402000
raw: 0000000000000000 ffff8880915d0680 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8880915d1a00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8880915d1a80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff8880915d1b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff8880915d1b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8880915d1c00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.