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BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 net/l2tp/l2tp_core.c:917
Read of size 4 at addr ffff8801b79a0780 by task syzkaller646172/3775
CPU: 0 PID: 3775 Comm: syzkaller646172 Not tainted 4.9.92-g7cd9561 #1
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
ffff8801c37b7cb0 ffffffff81d9c489 ffffea0006de6800 ffff8801b79a0780
0000000000000000 ffff8801b79a0780 ffffffff82ef0be0 ffff8801c37b7ce8
ffffffff8156556b ffff8801b79a0780 0000000000000004 0000000000000000
Call Trace:
[<ffffffff81d9c489>] __dump_stack lib/dump_stack.c:15 [inline]
[<ffffffff81d9c489>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
[<ffffffff8156556b>] print_address_description+0x6c/0x234 mm/kasan/report.c:256
[<ffffffff815657df>] kasan_report_error mm/kasan/report.c:355 [inline]
[<ffffffff815657df>] kasan_report.cold.6+0xac/0x2f5 mm/kasan/report.c:412
[<ffffffff815395d4>] __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:432
[<ffffffff83597774>] l2tp_session_queue_purge+0xf4/0x100 net/l2tp/l2tp_core.c:917
[<ffffffff835a345b>] pppol2tp_release+0x1fb/0x2e0 net/l2tp/l2tp_ppp.c:492
[<ffffffff82ef0ab6>] sock_release+0x96/0x1c0 net/socket.c:599
[<ffffffff82ef0bf6>] sock_close+0x16/0x20 net/socket.c:1046
[<ffffffff81575c83>] __fput+0x263/0x700 fs/file_table.c:208
[<ffffffff815761a5>] ____fput+0x15/0x20 fs/file_table.c:244
[<ffffffff81195dec>] task_work_run+0x10c/0x180 kernel/task_work.c:116
[<ffffffff8100559c>] tracehook_notify_resume include/linux/tracehook.h:191 [inline]
[<ffffffff8100559c>] exit_to_usermode_loop+0xfc/0x120 arch/x86/entry/common.c:161
[<ffffffff810064d4>] prepare_exit_to_usermode arch/x86/entry/common.c:191 [inline]
[<ffffffff810064d4>] syscall_return_slowpath arch/x86/entry/common.c:260 [inline]
[<ffffffff810064d4>] do_syscall_64+0x364/0x490 arch/x86/entry/common.c:287
[<ffffffff838d58d3>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Allocated by task 3774:
save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
save_stack+0x43/0xd0 mm/kasan/kasan.c:505
set_track mm/kasan/kasan.c:517 [inline]
kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:609
__kmalloc+0x11d/0x300 mm/slub.c:3741
kmalloc include/linux/slab.h:495 [inline]
kzalloc include/linux/slab.h:636 [inline]
l2tp_session_create+0x38/0x1760 net/l2tp/l2tp_core.c:1843
pppol2tp_connect+0x10c5/0x18e0 net/l2tp/l2tp_ppp.c:711
SYSC_connect+0x1b8/0x300 net/socket.c:1562
SyS_connect+0x24/0x30 net/socket.c:1543
do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Freed by task 3774:
save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
save_stack+0x43/0xd0 mm/kasan/kasan.c:505
set_track mm/kasan/kasan.c:517 [inline]
kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:582
slab_free_hook mm/slub.c:1355 [inline]
slab_free_freelist_hook mm/slub.c:1377 [inline]
slab_free mm/slub.c:2958 [inline]
kfree+0xfb/0x310 mm/slub.c:3878
l2tp_session_free+0x166/0x200 net/l2tp/l2tp_core.c:1770
l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:297 [inline]
l2tp_tunnel_closeall+0x284/0x350 net/l2tp/l2tp_core.c:1373
l2tp_udp_encap_destroy+0x87/0xe0 net/l2tp/l2tp_core.c:1394
udpv6_destroy_sock+0xb1/0xd0 net/ipv6/udp.c:1336
sk_common_release+0x6d/0x300 net/core/sock.c:2727
udp_lib_close+0x15/0x20 include/net/udp.h:203
inet_release+0xff/0x1d0 net/ipv4/af_inet.c:434
inet6_release+0x50/0x70 net/ipv6/af_inet6.c:440
sock_release+0x96/0x1c0 net/socket.c:599
sock_close+0x16/0x20 net/socket.c:1046
__fput+0x263/0x700 fs/file_table.c:208
____fput+0x15/0x20 fs/file_table.c:244
task_work_run+0x10c/0x180 kernel/task_work.c:116
tracehook_notify_resume include/linux/tracehook.h:191 [inline]
exit_to_usermode_loop+0xfc/0x120 arch/x86/entry/common.c:161
prepare_exit_to_usermode arch/x86/entry/common.c:191 [inline]
syscall_return_slowpath arch/x86/entry/common.c:260 [inline]
do_syscall_64+0x364/0x490 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_swapgs+0x5d/0xdb
The buggy address belongs to the object at ffff8801b79a0780
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
512-byte region [ffff8801b79a0780, ffff8801b79a0980)
The buggy address belongs to the page:
page:ffffea0006de6800 count:1 mapcount:0 mapping: (null) index:0xffff8801b79a1b80 compound_mapcount: 0
flags: 0x8000000000004080(slab|head)
page dumped because: kasan: bad access detected
Memory state around the buggy address:
ffff8801b79a0680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801b79a0700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8801b79a0780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8801b79a0800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801b79a0880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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