KASAN: use-after-free Read in l2tp_session_queue_purge

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: b98aebd2 Linux 4.14.150
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1333347b600000
kernel config: https://syzkaller.appspot.com/x/.config?x=c52c93b368dac5a7
dashboard link: https://syzkaller.appspot.com/bug?extid=1b475c743d59e27bc4cc
compiler: gcc (GCC) 9.0.0 20181231 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+1b475c...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf2/0x100
net/l2tp/l2tp_core.c:874
Read of size 4 at addr ffff88806c097580 by task syz-executor.1/15392

CPU: 1 PID: 15392 Comm: syz-executor.1 Not tainted 4.14.150 #0
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+0x138/0x197 lib/dump_stack.c:53
print_address_description.cold+0x7c/0x1dc mm/kasan/report.c:252
kasan_report_error mm/kasan/report.c:351 [inline]
kasan_report mm/kasan/report.c:409 [inline]
kasan_report.cold+0xa9/0x2af mm/kasan/report.c:393
__asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:429
l2tp_session_queue_purge+0xf2/0x100 net/l2tp/l2tp_core.c:874
l2tp_tunnel_closeall+0x20c/0x380 net/l2tp/l2tp_core.c:1337
l2tp_udp_encap_destroy+0x99/0x100 net/l2tp/l2tp_core.c:1366
udpv6_destroy_sock+0xb3/0xd0 net/ipv6/udp.c:1444
sk_common_release+0x6b/0x310 net/core/sock.c:2989
udp_lib_close+0x16/0x20 include/net/udp.h:203
inet_release+0xec/0x1c0 net/ipv4/af_inet.c:425
inet6_release+0x53/0x80 net/ipv6/af_inet6.c:450
__sock_release+0xce/0x2b0 net/socket.c:602
sock_close+0x1b/0x30 net/socket.c:1139
__fput+0x275/0x7a0 fs/file_table.c:210
____fput+0x16/0x20 fs/file_table.c:244
task_work_run+0x114/0x190 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:191 [inline]
exit_to_usermode_loop+0x1da/0x220 arch/x86/entry/common.c:164
prepare_exit_to_usermode arch/x86/entry/common.c:199 [inline]
syscall_return_slowpath arch/x86/entry/common.c:270 [inline]
do_syscall_64+0x4bc/0x640 arch/x86/entry/common.c:297
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x4139c1
RSP: 002b:00007fff5db0db60 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000006 RCX: 00000000004139c1
RDX: 0000000000000000 RSI: 0000000000000081 RDI: 0000000000000005
RBP: 0000000000000000 R08: 00000000007616b8 R09: ffffffffffffffff
R10: 00007fff5db0dc30 R11: 0000000000000293 R12: 000000000075bf20
R13: 0000000000000004 R14: 00000000007616c0 R15: 000000000075bf2c

Allocated by task 15409:
save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
save_stack+0x45/0xd0 mm/kasan/kasan.c:447
set_track mm/kasan/kasan.c:459 [inline]
kasan_kmalloc mm/kasan/kasan.c:551 [inline]
kasan_kmalloc+0xce/0xf0 mm/kasan/kasan.c:529
__do_kmalloc mm/slab.c:3720 [inline]
__kmalloc+0x15d/0x7a0 mm/slab.c:3729
kmalloc include/linux/slab.h:493 [inline]
kzalloc include/linux/slab.h:661 [inline]
l2tp_session_create+0x38/0x1600 net/l2tp/l2tp_core.c:1791
pppol2tp_connect+0x11bf/0x18b0 net/l2tp/l2tp_ppp.c:721
SYSC_connect+0x1f6/0x2d0 net/socket.c:1655
SyS_connect+0x24/0x30 net/socket.c:1636
do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x42/0xb7

Freed by task 15409:
save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
save_stack+0x45/0xd0 mm/kasan/kasan.c:447
set_track mm/kasan/kasan.c:459 [inline]
kasan_slab_free+0x75/0xc0 mm/kasan/kasan.c:524
__cache_free mm/slab.c:3496 [inline]
kfree+0xcc/0x270 mm/slab.c:3815
l2tp_session_free+0x176/0x210 net/l2tp/l2tp_core.c:1714
l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:300 [inline]
pppol2tp_session_destruct+0xd8/0x110 net/l2tp/l2tp_ppp.c:460
__sk_destruct+0x4f/0x580 net/core/sock.c:1556
sk_destruct+0xa4/0xd0 net/core/sock.c:1596
__sk_free+0x54/0x230 net/core/sock.c:1604
sk_free+0x35/0x40 net/core/sock.c:1615
sock_put include/net/sock.h:1653 [inline]
pppol2tp_release+0x244/0x300 net/l2tp/l2tp_ppp.c:501
__sock_release+0xce/0x2b0 net/socket.c:602
sock_close+0x1b/0x30 net/socket.c:1139
__fput+0x275/0x7a0 fs/file_table.c:210
____fput+0x16/0x20 fs/file_table.c:244
task_work_run+0x114/0x190 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:191 [inline]
exit_to_usermode_loop+0x1da/0x220 arch/x86/entry/common.c:164
prepare_exit_to_usermode arch/x86/entry/common.c:199 [inline]
syscall_return_slowpath arch/x86/entry/common.c:270 [inline]
do_syscall_64+0x4bc/0x640 arch/x86/entry/common.c:297
entry_SYSCALL_64_after_hwframe+0x42/0xb7

The buggy address belongs to the object at ffff88806c097580
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
512-byte region [ffff88806c097580, ffff88806c097780)
The buggy address belongs to the page:
page:ffffea0001b025c0 count:1 mapcount:0 mapping:ffff88806c097080 index:0x0
flags: 0x1fffc0000000100(slab)
raw: 01fffc0000000100 ffff88806c097080 0000000000000000 0000000100000006
raw: ffffea00024ec0a0 ffffea0002634c60 ffff8880aa800940 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88806c097480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88806c097500: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff88806c097580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88806c097600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88806c097680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit: b98aebd2 Linux 4.14.150
git tree: linux-4.14.y

console output: https://syzkaller.appspot.com/x/log.txt?x=108a5a97600000

kernel config: https://syzkaller.appspot.com/x/.config?x=c52c93b368dac5a7
dashboard link: https://syzkaller.appspot.com/bug?extid=1b475c743d59e27bc4cc
compiler: gcc (GCC) 9.0.0 20181231 (experimental)

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11d85ce4e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+1b475c...@syzkaller.appspotmail.com

audit: type=1400 audit(1572246139.146:38): avc: denied { map } for
pid=6982 comm="syz-executor.0"
path=2F6D656D66643A73656375726974792E73656C696E7578202864656C6574656429
dev="tmpfs" ino=26873
scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023
tcontext=unconfined_u:object_r:tmpfs_t:s0 tclass=file permissive=1
hrtimer: interrupt took 42858 ns

==================================================================
BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf2/0x100
net/l2tp/l2tp_core.c:874

Read of size 4 at addr ffff8880902b0000 by task syz-executor.0/7094

CPU: 0 PID: 7094 Comm: syz-executor.0 Not tainted 4.14.150 #0

RIP: 0033:0x413ad1
RSP: 002b:00007ffea8c928e0 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000007 RCX: 0000000000413ad1
RDX: 0000000000000000 RSI: 0000000000000081 RDI: 0000000000000006
RBP: 0000000000000000 R08: 0000000000760f58 R09: ffffffffffffffff
R10: 00007ffea8c929b0 R11: 0000000000000293 R12: 000000000075bf20
R13: 0000000000000003 R14: 0000000000760f60 R15: 000000000075bf2c

Allocated by task 7095:

save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
save_stack+0x45/0xd0 mm/kasan/kasan.c:447
set_track mm/kasan/kasan.c:459 [inline]
kasan_kmalloc mm/kasan/kasan.c:551 [inline]
kasan_kmalloc+0xce/0xf0 mm/kasan/kasan.c:529
__do_kmalloc mm/slab.c:3720 [inline]
__kmalloc+0x15d/0x7a0 mm/slab.c:3729
kmalloc include/linux/slab.h:493 [inline]
kzalloc include/linux/slab.h:661 [inline]
l2tp_session_create+0x38/0x1600 net/l2tp/l2tp_core.c:1791
pppol2tp_connect+0x11bf/0x18b0 net/l2tp/l2tp_ppp.c:721
SYSC_connect+0x1f6/0x2d0 net/socket.c:1655
SyS_connect+0x24/0x30 net/socket.c:1636
do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x42/0xb7

Freed by task 7095:

The buggy address belongs to the object at ffff8880902b0000

which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of

512-byte region [ffff8880902b0000, ffff8880902b0200)

The buggy address belongs to the page:

page:ffffea000240ac00 count:1 mapcount:0 mapping:ffff8880902b0000 index:0x0
flags: 0x1fffc0000000100(slab)
raw: 01fffc0000000100 ffff8880902b0000 0000000000000000 0000000100000006
raw: ffffea00023fbf20 ffffea0002362aa0 ffff8880aa800940 0000000000000000

page dumped because: kasan: bad access detected

Memory state around the buggy address:

ffff8880902aff00: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
ffff8880902aff80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff8880902b0000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8880902b0080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880902b0100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================