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BUG: KASAN: use-after-free in ifname_compare_aligned include/linux/netfilter/x_tables.h:369 [inline]
BUG: KASAN: use-after-free in ip6_packet_match net/ipv6/netfilter/ip6_tables.c:89 [inline]
BUG: KASAN: use-after-free in ip6t_do_table+0x14e2/0x17e0 net/ipv6/netfilter/ip6_tables.c:333
Read of size 8 at addr ffff8801c8e50000 by task syz-executor.2/5496

CPU: 1 PID: 5496 Comm: syz-executor.2 Not tainted 4.9.141+ #1
 ffff8801d83ff020 ffffffff81b42e79 ffffea0007239400 ffff8801c8e50000
 0000000000000000 ffff8801c8e50000 dffffc0000000000 ffff8801d83ff058
 ffffffff815009b8 ffff8801c8e50000 0000000000000008 0000000000000000
Call Trace:
 [<ffffffff81b42e79>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81b42e79>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff815009b8>] print_address_description+0x6c/0x234 mm/kasan/report.c:256
 [<ffffffff81500dc2>] kasan_report_error mm/kasan/report.c:355 [inline]
 [<ffffffff81500dc2>] kasan_report.cold.6+0x242/0x2fe mm/kasan/report.c:412
 [<ffffffff814f3074>] __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
 [<ffffffff8277f202>] ifname_compare_aligned include/linux/netfilter/x_tables.h:369 [inline]
 [<ffffffff8277f202>] ip6_packet_match net/ipv6/netfilter/ip6_tables.c:89 [inline]
 [<ffffffff8277f202>] ip6t_do_table+0x14e2/0x17e0 net/ipv6/netfilter/ip6_tables.c:333
 [<ffffffff82787bd7>] ip6t_mangle_out net/ipv6/netfilter/ip6table_mangle.c:63 [inline]
 [<ffffffff82787bd7>] ip6table_mangle_hook+0x2d7/0x660 net/ipv6/netfilter/ip6table_mangle.c:85
 [<ffffffff823ddae6>] nf_iterate+0x126/0x310 net/netfilter/core.c:324
 [<ffffffff823ddde4>] nf_hook_slow+0x114/0x1e0 net/netfilter/core.c:355
 [<ffffffff827bcbe4>] nf_hook_thresh include/linux/netfilter.h:191 [inline]
 [<ffffffff827bcbe4>] nf_hook include/linux/netfilter.h:203 [inline]
 [<ffffffff827bcbe4>] __ip6_local_out+0x484/0x620 net/ipv6/output_core.c:164
 [<ffffffff827bcda9>] ip6_local_out+0x29/0x180 net/ipv6/output_core.c:174
 [<ffffffff826a4891>] ip6_send_skb+0xa1/0x340 net/ipv6/ip6_output.c:1751
 [<ffffffff82706689>] udp_v6_send_skb+0x429/0xe70 net/ipv6/udp.c:974
 [<ffffffff827072fd>] udp_v6_push_pending_frames+0x22d/0x340 net/ipv6/udp.c:1007
 [<ffffffff827092b1>] udpv6_sendmsg+0x1dc1/0x2430 net/ipv6/udp.c:1273
 [<ffffffff825952f3>] inet_sendmsg+0x203/0x4d0 net/ipv4/af_inet.c:770
 [<ffffffff822a063b>] sock_sendmsg_nosec net/socket.c:648 [inline]
 [<ffffffff822a063b>] sock_sendmsg+0xbb/0x110 net/socket.c:658
 [<ffffffff822a209a>] ___sys_sendmsg+0x47a/0x840 net/socket.c:1982
 [<ffffffff822a55a1>] __sys_sendmmsg+0x161/0x3d0 net/socket.c:2072
 [<ffffffff822a5845>] SYSC_sendmmsg net/socket.c:2103 [inline]
 [<ffffffff822a5845>] SyS_sendmmsg+0x35/0x60 net/socket.c:2098
 [<ffffffff810056ef>] do_syscall_64+0x19f/0x550 arch/x86/entry/common.c:285
 [<ffffffff82817893>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb

The buggy address belongs to the page:
page:ffffea0007239400 count:0 mapcount:-127 mapping:          (null) index:0x0
flags: 0x4000000000000000()
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801c8e4ff00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8801c8e4ff80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8801c8e50000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                   ^
 ffff8801c8e50080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8801c8e50100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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