==================================================================
BUG: KASAN: slab-out-of-bounds in _decode_session6+0x124c/0x1370 net/ipv6/xfrm6_policy.c:159
Read of size 1 at addr ffff8801bb4d4987 by task syz-executor0/15676

CPU: 0 PID: 15676 Comm: syz-executor0 Not tainted 4.14.67+ #1
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0xb9/0x11b lib/dump_stack.c:53
 print_address_description+0x60/0x22b mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report.cold.6+0x11b/0x2dd mm/kasan/report.c:409
 _decode_session6+0x124c/0x1370 net/ipv6/xfrm6_policy.c:159
 __xfrm_decode_session+0x64/0x100 net/xfrm/xfrm_policy.c:2366
 xfrm_decode_session include/net/xfrm.h:1175 [inline]
 vti6_tnl_xmit+0x31b/0x1550 net/ipv6/ip6_vti.c:549
 __netdev_start_xmit include/linux/netdevice.h:4023 [inline]
 netdev_start_xmit include/linux/netdevice.h:4032 [inline]
 xmit_one net/core/dev.c:2987 [inline]
 dev_hard_start_xmit+0x191/0x890 net/core/dev.c:3003
 __dev_queue_xmit+0x13d9/0x1f40 net/core/dev.c:3503
 __bpf_tx_skb net/core/filter.c:1708 [inline]
 __bpf_redirect_common net/core/filter.c:1746 [inline]
 __bpf_redirect+0x5b0/0x990 net/core/filter.c:1753
 ____bpf_clone_redirect net/core/filter.c:1786 [inline]
 bpf_clone_redirect+0x1d4/0x2b0 net/core/filter.c:1758
 ___bpf_prog_run+0x248e/0x5c70 kernel/bpf/core.c:1012

Allocated by task 15676:
 save_stack mm/kasan/kasan.c:447 [inline]
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc.part.1+0x4f/0xd0 mm/kasan/kasan.c:551
 slab_post_alloc_hook mm/slab.h:442 [inline]
 slab_alloc_node mm/slub.c:2723 [inline]
 slab_alloc mm/slub.c:2731 [inline]
 __kmalloc_track_caller+0x104/0x300 mm/slub.c:4288
 __kmalloc_reserve.isra.8+0x2f/0xc0 net/core/skbuff.c:137
 pskb_expand_head+0x117/0xb30 net/core/skbuff.c:1461
 skb_ensure_writable+0x237/0x2e0 net/core/skbuff.c:5007
 __bpf_try_make_writable net/core/filter.c:1403 [inline]
 bpf_try_make_writable net/core/filter.c:1409 [inline]
 bpf_try_make_head_writable net/core/filter.c:1417 [inline]
 ____bpf_clone_redirect net/core/filter.c:1780 [inline]
 bpf_clone_redirect+0x119/0x2b0 net/core/filter.c:1758
 ___bpf_prog_run+0x248e/0x5c70 kernel/bpf/core.c:1012

Freed by task 13968:
 save_stack mm/kasan/kasan.c:447 [inline]
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0xac/0x190 mm/kasan/kasan.c:524
 slab_free_hook mm/slub.c:1389 [inline]
 slab_free_freelist_hook mm/slub.c:1410 [inline]
 slab_free mm/slub.c:2966 [inline]
 kfree+0xf5/0x310 mm/slub.c:3897
 skb_free_head+0x83/0xa0 net/core/skbuff.c:550
 skb_release_data+0x495/0x610 net/core/skbuff.c:570
 skb_release_all+0x46/0x60 net/core/skbuff.c:627
 __kfree_skb net/core/skbuff.c:641 [inline]
 kfree_skb+0xc8/0x340 net/core/skbuff.c:659
 unix_dgram_sendmsg+0x5e5/0xf50 net/unix/af_unix.c:1818
 unix_seqpacket_sendmsg+0xed/0x160 net/unix/af_unix.c:2062
 sock_sendmsg_nosec net/socket.c:645 [inline]
 sock_sendmsg+0xb5/0x100 net/socket.c:655
 ___sys_sendmsg+0x41d/0x890 net/socket.c:2061
 __sys_sendmmsg+0x13d/0x360 net/socket.c:2151
 SYSC_sendmmsg net/socket.c:2182 [inline]
 SyS_sendmmsg+0x2f/0x50 net/socket.c:2177
 do_syscall_64+0x19b/0x4b0 arch/x86/entry/common.c:289
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

The buggy address belongs to the object at ffff8801bb4d4780
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 7 bytes to the right of
 512-byte region [ffff8801bb4d4780, ffff8801bb4d4980)
The buggy address belongs to the page:
page:ffffea0006ed3500 count:1 mapcount:0 mapping:          (null) index:0x0 compound_mapcount: 0
flags: 0x4000000000008100(slab|head)
raw: 4000000000008100 0000000000000000 0000000000000000 00000001800c000c
raw: 0000000000000000 0000000a00000001 ffff8801da802c00 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801bb4d4880: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8801bb4d4900: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff8801bb4d4980: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                   ^
 ffff8801bb4d4a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801bb4d4a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================