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BUG: KASAN: use-after-free in atomic_sub_return include/asm-generic/atomic-instrumented.h:258 [inline]
BUG: KASAN: use-after-free in skb_release_data+0x101/0x770 net/core/skbuff.c:563
Write of size 4 at addr ffff8881d6b88fe4 by task syz-executor.2/14833

CPU: 1 PID: 14833 Comm: syz-executor.2 Not tainted 4.14.139+ #36
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0xca/0x134 lib/dump_stack.c:53
 print_address_description+0x60/0x226 mm/kasan/report.c:187
 __kasan_report.cold+0x1a/0x41 mm/kasan/report.c:316
 atomic_sub_return include/asm-generic/atomic-instrumented.h:258 [inline]
 skb_release_data+0x101/0x770 net/core/skbuff.c:563
 skb_release_all+0x46/0x60 net/core/skbuff.c:631
 __kfree_skb net/core/skbuff.c:645 [inline]
 kfree_skb+0xe3/0x370 net/core/skbuff.c:663
 ip6_tnl_start_xmit+0x7ee/0x1b00 net/ipv6/ip6_tunnel.c:1417
 __netdev_start_xmit include/linux/netdevice.h:4033 [inline]
 netdev_start_xmit include/linux/netdevice.h:4042 [inline]
 xmit_one net/core/dev.c:3009 [inline]
 dev_hard_start_xmit+0x19f/0x8c0 net/core/dev.c:3025
 __dev_queue_xmit+0x11e0/0x1d00 net/core/dev.c:3525
 packet_sendmsg_spkt+0xb4f/0x1210 net/packet/af_packet.c:2014
 sock_sendmsg_nosec net/socket.c:646 [inline]
 sock_sendmsg+0xb7/0x100 net/socket.c:656
 ___sys_sendmsg+0x368/0x890 net/socket.c:2062
 __sys_sendmmsg+0x13c/0x360 net/socket.c:2152
 SYSC_sendmmsg net/socket.c:2183 [inline]
 SyS_sendmmsg+0x2f/0x50 net/socket.c:2178
 do_syscall_64+0x19b/0x520 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x459829
RSP: 002b:00007f25f62c3c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 0000000000459829
RDX: 0000000000000001 RSI: 00000000200021c0 RDI: 0000000000000003
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000048050 R11: 0000000000000246 R12: 00007f25f62c46d4
R13: 00000000004c700e R14: 00000000004dc648 R15: 00000000ffffffff

Allocated by task 14833:
 save_stack mm/kasan/common.c:76 [inline]
 set_track mm/kasan/common.c:85 [inline]
 __kasan_kmalloc.part.0+0x53/0xc0 mm/kasan/common.c:495
 slab_post_alloc_hook mm/slab.h:439 [inline]
 slab_alloc_node mm/slub.c:2758 [inline]
 slab_alloc mm/slub.c:2766 [inline]
 __kmalloc_track_caller+0xf1/0x310 mm/slub.c:4333
 __kmalloc_reserve.isra.0+0x2d/0xc0 net/core/skbuff.c:137
 __alloc_skb+0x118/0x5c0 net/core/skbuff.c:205
 alloc_skb include/linux/skbuff.h:980 [inline]
 sock_wmalloc+0xb6/0x110 net/core/sock.c:1925
 packet_sendmsg_spkt+0x3bb/0x1210 net/packet/af_packet.c:1962
 sock_sendmsg_nosec net/socket.c:646 [inline]
 sock_sendmsg+0xb7/0x100 net/socket.c:656
 ___sys_sendmsg+0x368/0x890 net/socket.c:2062
 __sys_sendmmsg+0x13c/0x360 net/socket.c:2152
 SYSC_sendmmsg net/socket.c:2183 [inline]
 SyS_sendmmsg+0x2f/0x50 net/socket.c:2178
 do_syscall_64+0x19b/0x520 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
 0xffffffffffffffff

Freed by task 14833:
 save_stack mm/kasan/common.c:76 [inline]
 set_track mm/kasan/common.c:85 [inline]
 __kasan_slab_free+0x164/0x210 mm/kasan/common.c:457
 slab_free_hook mm/slub.c:1403 [inline]
 slab_free_freelist_hook mm/slub.c:1430 [inline]
 slab_free mm/slub.c:3005 [inline]
 kfree+0xfa/0x320 mm/slub.c:3942
 skb_free_head+0x83/0xa0 net/core/skbuff.c:554
 skb_release_data+0x4e5/0x770 net/core/skbuff.c:574
 skb_release_all+0x46/0x60 net/core/skbuff.c:631
 __kfree_skb net/core/skbuff.c:645 [inline]
 consume_skb+0xdc/0x360 net/core/skbuff.c:705
 packet_rcv+0xdf/0x1290 net/packet/af_packet.c:2178
 dev_queue_xmit_nit+0x6e1/0x970 net/core/dev.c:1975
 xmit_one net/core/dev.c:3005 [inline]
 dev_hard_start_xmit+0xa3/0x8c0 net/core/dev.c:3025
 __dev_queue_xmit+0x11e0/0x1d00 net/core/dev.c:3525
 packet_sendmsg_spkt+0xb4f/0x1210 net/packet/af_packet.c:2014
 sock_sendmsg_nosec net/socket.c:646 [inline]
 sock_sendmsg+0xb7/0x100 net/socket.c:656
 ___sys_sendmsg+0x368/0x890 net/socket.c:2062
 __sys_sendmmsg+0x13c/0x360 net/socket.c:2152
 SYSC_sendmmsg net/socket.c:2183 [inline]
 SyS_sendmmsg+0x2f/0x50 net/socket.c:2178
 do_syscall_64+0x19b/0x520 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
 0xffffffffffffffff

The buggy address belongs to the object at ffff8881d6b88f00
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 228 bytes inside of
 512-byte region [ffff8881d6b88f00, ffff8881d6b89100)
The buggy address belongs to the page:
page:ffffea00075ae200 count:1 mapcount:0 mapping:          (null) index:0x0 compound_mapcount: 0
flags: 0x4000000000010200(slab|head)
raw: 4000000000010200 0000000000000000 0000000000000000 00000001800c000c
raw: ffffea0007304b00 0000000200000002 ffff8881da802c00 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8881d6b88e80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8881d6b88f00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8881d6b88f80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                       ^
 ffff8881d6b89000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8881d6b89080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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