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SubjectKASAN: use-after-free Read in tomoyo_realpath_from_path

syzbot found the following crash on:

HEAD commit: 788a0249 Merge tag 'arc-5.2-rc4' of git://
git tree: upstream
console output:
kernel config:
dashboard link:
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:

IMPORTANT: if you fix the bug, please add the following tag to the commit:

BUG: KASAN: use-after-free in tomoyo_get_socket_name
security/tomoyo/realpath.c:238 [inline]
BUG: KASAN: use-after-free in tomoyo_realpath_from_path+0x722/0x7a0
Read of size 2 at addr ffff8880a91276d0 by task syz-executor.3/17397

CPU: 0 PID: 17397 Comm: syz-executor.3 Not tainted 5.2.0-rc3+ #12
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x172/0x1f0 lib/dump_stack.c:113
print_address_description.cold+0x7c/0x20d mm/kasan/report.c:188
__kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317
kasan_report+0x12/0x20 mm/kasan/common.c:614
__asan_report_load2_noabort+0x14/0x20 mm/kasan/generic_report.c:130
tomoyo_get_socket_name security/tomoyo/realpath.c:238 [inline]
tomoyo_realpath_from_path+0x722/0x7a0 security/tomoyo/realpath.c:284
tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
tomoyo_check_open_permission+0x2a8/0x3f0 security/tomoyo/file.c:771
tomoyo_file_open security/tomoyo/tomoyo.c:319 [inline]
tomoyo_file_open+0xa9/0xd0 security/tomoyo/tomoyo.c:314
security_file_open+0x71/0x300 security/security.c:1454
do_dentry_open+0x373/0x1250 fs/open.c:765
vfs_open+0xa0/0xd0 fs/open.c:887
do_last fs/namei.c:3416 [inline]
path_openat+0x10e9/0x46d0 fs/namei.c:3533
do_filp_open+0x1a1/0x280 fs/namei.c:3563
do_sys_open+0x3fe/0x5d0 fs/open.c:1070
__do_sys_open fs/open.c:1088 [inline]
__se_sys_open fs/open.c:1083 [inline]
__x64_sys_open+0x7e/0xc0 fs/open.c:1083
do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
RIP: 0033:0x413161
Code: 75 14 b8 02 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 04 19 00 00 c3 48
83 ec 08 e8 0a fa ff ff 48 89 04 24 b8 02 00 00 00 0f 05 <48> 8b 3c 24 48
89 c2 e8 53 fa ff ff 48 89 d0 48 83 c4 08 48 3d 01
RSP: 002b:00007f65230f8bb0 EFLAGS: 00000293 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 0000000000413161
RDX: fffffffffffffffa RSI: 0000000000000000 RDI: 00007f65230f8bd0
RBP: 000000000075c060 R08: 0000000000000050 R09: 000000000000000f
R10: 0000000000000004 R11: 0000000000000293 R12: 00007f65230f96d4
R13: 00000000004c83f6 R14: 00000000004dea40 R15: 00000000ffffffff

Allocated by task 17373:
save_stack+0x23/0x90 mm/kasan/common.c:71
set_track mm/kasan/common.c:79 [inline]
__kasan_kmalloc mm/kasan/common.c:489 [inline]
__kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:462
kasan_kmalloc+0x9/0x10 mm/kasan/common.c:503
__do_kmalloc mm/slab.c:3660 [inline]
__kmalloc+0x15c/0x740 mm/slab.c:3669
kmalloc include/linux/slab.h:552 [inline]
sk_prot_alloc+0x19c/0x2e0 net/core/sock.c:1602
sk_alloc+0x39/0xf70 net/core/sock.c:1656
base_sock_create drivers/isdn/mISDN/socket.c:758 [inline]
mISDN_sock_create+0xb4/0x3a0 drivers/isdn/mISDN/socket.c:780
__sock_create+0x3d8/0x730 net/socket.c:1424
sock_create net/socket.c:1475 [inline]
__sys_socket+0x103/0x220 net/socket.c:1517
__do_sys_socket net/socket.c:1526 [inline]
__se_sys_socket net/socket.c:1524 [inline]
__x64_sys_socket+0x73/0xb0 net/socket.c:1524
do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301

Freed by task 17371:
save_stack+0x23/0x90 mm/kasan/common.c:71
set_track mm/kasan/common.c:79 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/common.c:451
kasan_slab_free+0xe/0x10 mm/kasan/common.c:459
__cache_free mm/slab.c:3432 [inline]
kfree+0xcf/0x220 mm/slab.c:3755
sk_prot_free net/core/sock.c:1639 [inline]
__sk_destruct+0x4f7/0x6e0 net/core/sock.c:1725
sk_destruct+0x7b/0x90 net/core/sock.c:1733
__sk_free+0xce/0x300 net/core/sock.c:1744
sk_free+0x42/0x50 net/core/sock.c:1755
sock_put include/net/sock.h:1723 [inline]
base_sock_release+0x269/0x279 drivers/isdn/mISDN/socket.c:628
__sock_release+0xce/0x2a0 net/socket.c:601
sock_close+0x1b/0x30 net/socket.c:1273
__fput+0x2ff/0x890 fs/file_table.c:280
____fput+0x16/0x20 fs/file_table.c:313
task_work_run+0x145/0x1c0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:185 [inline]
exit_to_usermode_loop+0x273/0x2c0 arch/x86/entry/common.c:168
prepare_exit_to_usermode arch/x86/entry/common.c:199 [inline]
syscall_return_slowpath arch/x86/entry/common.c:279 [inline]
do_syscall_64+0x58e/0x680 arch/x86/entry/common.c:304

The buggy address belongs to the object at ffff8880a91276c0
which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 16 bytes inside of
2048-byte region [ffff8880a91276c0, ffff8880a9127ec0)
The buggy address belongs to the page:
page:ffffea0002a44980 refcount:1 mapcount:0 mapping:ffff8880aa400c40
index:0x0 compound_mapcount: 0
flags: 0x1fffc0000010200(slab|head)
raw: 01fffc0000010200 ffffea00022c9f88 ffffea0002234408 ffff8880aa400c40
raw: 0000000000000000 ffff8880a91265c0 0000000100000003 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8880a9127580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880a9127600: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
> ffff8880a9127680: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
ffff8880a9127700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880a9127780: 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.
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