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BUG: KASAN: slab-out-of-bounds in ip6_dst_idev include/net/ip6_fib.h:192 [inline]
BUG: KASAN: slab-out-of-bounds in ip6_xmit+0x1f76/0x2260 net/ipv6/ip6_output.c:264
Read of size 8 at addr ffff8801b900a018 by task syzkaller777193/4505

CPU: 1 PID: 4505 Comm: syzkaller777193 Not tainted 4.16.0-rc4+ #269
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x24d lib/dump_stack.c:53
 print_address_description+0x73/0x250 mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report+0x23c/0x360 mm/kasan/report.c:412
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
 ip6_dst_idev include/net/ip6_fib.h:192 [inline]
 ip6_xmit+0x1f76/0x2260 net/ipv6/ip6_output.c:264
 inet6_csk_xmit+0x2fc/0x580 net/ipv6/inet6_connection_sock.c:139
 l2tp_xmit_core net/l2tp/l2tp_core.c:1053 [inline]
 l2tp_xmit_skb+0x105f/0x1410 net/l2tp/l2tp_core.c:1148
 pppol2tp_sendmsg+0x470/0x670 net/l2tp/l2tp_ppp.c:341
 sock_sendmsg_nosec net/socket.c:629 [inline]
 sock_sendmsg+0xca/0x110 net/socket.c:639
 ___sys_sendmsg+0x767/0x8b0 net/socket.c:2047
 __sys_sendmsg+0xe5/0x210 net/socket.c:2081
 SYSC_sendmsg net/socket.c:2092 [inline]
 SyS_sendmsg+0x2d/0x50 net/socket.c:2088
 do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x443b19
RSP: 002b:00000000007ef0e8 EFLAGS: 00000217 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00000000ffffffff RCX: 0000000000443b19
RDX: 0000000000000081 RSI: 000000002037ffc8 RDI: 0000000000000004
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000217 R12: 0000000000000000
R13: 0000000000000003 R14: 0000000000000000 R15: 0000000000001380

Allocated by task 2962:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:552
 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:489
 kmem_cache_alloc+0x12e/0x760 mm/slab.c:3541
 getname_flags+0xcb/0x580 fs/namei.c:138
 user_path_at_empty+0x2d/0x50 fs/namei.c:2568
 user_path_at include/linux/namei.h:57 [inline]
 SYSC_faccessat fs/open.c:384 [inline]
 SyS_faccessat fs/open.c:353 [inline]
 SYSC_access fs/open.c:431 [inline]
 SyS_access+0x22c/0x6a0 fs/open.c:429
 do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

Freed by task 2962:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:520
 kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:527
 __cache_free mm/slab.c:3485 [inline]
 kmem_cache_free+0x83/0x2a0 mm/slab.c:3743
 putname+0xee/0x130 fs/namei.c:258
 filename_lookup+0x315/0x500 fs/namei.c:2323
 user_path_at_empty+0x40/0x50 fs/namei.c:2568
 user_path_at include/linux/namei.h:57 [inline]
 SYSC_faccessat fs/open.c:384 [inline]
 SyS_faccessat fs/open.c:353 [inline]
 SYSC_access fs/open.c:431 [inline]
 SyS_access+0x22c/0x6a0 fs/open.c:429
 do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

The buggy address belongs to the object at ffff8801b900ac80
 which belongs to the cache names_cache of size 4096
The buggy address is located 3176 bytes to the left of
 4096-byte region [ffff8801b900ac80, ffff8801b900bc80)
The buggy address belongs to the page:
page:ffffea0006e40280 count:1 mapcount:0 mapping:ffff8801b900ac80 index:0x0 compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffff8801b900ac80 0000000000000000 0000000100000001
raw: ffffea0006e5d2a0 ffffea0006e5fba0 ffff8801da5d6600 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801b9009f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8801b9009f80: 00 00 00 00 fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8801b900a000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                            ^
 ffff8801b900a080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8801b900a100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
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