==================================================================
BUG: KASAN: use-after-free in __ip6_append_data.isra.3+0x3397/0x3460 net/ipv6/ip6_output.c:1375
Read of size 8 at addr ffff8801a54080f0 by task syz-executor.1/5992

CPU: 1 PID: 5992 Comm: syz-executor.1 Not tainted 4.9.141+ #1
 ffff880184377298 ffffffff81b42e79 ffffea0006950200 ffff8801a54080f0
 0000000000000000 ffff8801a54080f0 0000000000000008 ffff8801843772d0
 ffffffff815009b8 ffff8801a54080f0 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
 [<ffffffff82699877>] __ip6_append_data.isra.3+0x3397/0x3460 net/ipv6/ip6_output.c:1375
 [<ffffffff826a4ea1>] ip6_make_skb+0x291/0x480 net/ipv6/ip6_output.c:1831
 [<ffffffff82709379>] udpv6_sendmsg+0x1e89/0x2430 net/ipv6/udp.c:1240
 [<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:ffffea0006950200 count:0 mapcount:-127 mapping:          (null) index:0x0
flags: 0x4000000000000000()
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801a5407f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8801a5408000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff8801a5408080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                                             ^
 ffff8801a5408100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8801a5408180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
selinux_nlmsg_perm: 277 callbacks suppressed
SELinux: unrecognized netlink message: protocol=0 nlmsg_type=0 sclass=netlink_route_socket pig=6018 comm=syz-executor.1
SELinux: unrecognized netlink message: protocol=0 nlmsg_type=0 sclass=netlink_route_socket pig=5995 comm=syz-executor.4