KASAN: use-after-free Read in refcount_inc_not_zero_checked

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 19bb613a Linux 4.19.37
git tree: linux-4.19.y
console output: https://syzkaller.appspot.com/x/log.txt?x=12d7c362a00000
kernel config: https://syzkaller.appspot.com/x/.config?x=2f4f1677ff80cdff
dashboard link: https://syzkaller.appspot.com/bug?extid=e49a36b299ae130dcde1
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+e49a36...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in atomic_read
include/asm-generic/atomic-instrumented.h:21 [inline]
BUG: KASAN: use-after-free in refcount_inc_not_zero_checked+0x7b/0x200
lib/refcount.c:120
Read of size 4 at addr ffff8880a13ed1c0 by task syz-executor.5/11324

CPU: 1 PID: 11324 Comm: syz-executor.5 Not tainted 4.19.37 #5
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:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report mm/kasan/report.c:412 [inline]
kasan_report.cold+0x8c/0x2ba mm/kasan/report.c:396
check_memory_region_inline mm/kasan/kasan.c:260 [inline]
check_memory_region+0x123/0x190 mm/kasan/kasan.c:267
kasan_check_read+0x11/0x20 mm/kasan/kasan.c:272
atomic_read include/asm-generic/atomic-instrumented.h:21 [inline]
refcount_inc_not_zero_checked+0x7b/0x200 lib/refcount.c:120
refcount_inc_checked+0x17/0x70 lib/refcount.c:153
sock_hold include/net/sock.h:647 [inline]
nr_release+0x62/0x3c0 net/netrom/af_netrom.c:523
__sock_release+0xd3/0x2b0 net/socket.c:579
sock_close+0x1b/0x30 net/socket.c:1140
__fput+0x2df/0x8b0 fs/file_table.c:278
____fput+0x16/0x20 fs/file_table.c:309
task_work_run+0x14a/0x1c0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:193 [inline]
exit_to_usermode_loop+0x273/0x2c0 arch/x86/entry/common.c:166
prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
do_syscall_64+0x52d/0x610 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x412b61
Code: 75 14 b8 03 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 e4 1a 00 00 c3 48
83 ec 08 e8 0a fc ff ff 48 89 04 24 b8 03 00 00 00 0f 05 <48> 8b 3c 24 48
89 c2 e8 53 fc ff ff 48 89 d0 48 83 c4 08 48 3d 01
RSP: 002b:00007ffc1ff1fad0 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000007 RCX: 0000000000412b61
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000006
RBP: 0000000000000001 R08: 000000006bf79866 R09: 000000006bf7986a
R10: 00007ffc1ff1fbb0 R11: 0000000000000293 R12: 000000000073c900
R13: 000000000073c900 R14: 000000000003c97b R15: 000000000073c0ec

Allocated by task 11326:
save_stack+0x45/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
kasan_kmalloc mm/kasan/kasan.c:553 [inline]
kasan_kmalloc+0xce/0xf0 mm/kasan/kasan.c:531
__do_kmalloc mm/slab.c:3727 [inline]
__kmalloc+0x15d/0x750 mm/slab.c:3736
kmalloc include/linux/slab.h:520 [inline]
sk_prot_alloc+0x19c/0x2e0 net/core/sock.c:1469
sk_alloc+0x39/0xf70 net/core/sock.c:1523
nr_create+0xb9/0x5e0 net/netrom/af_netrom.c:436
__sock_create+0x3e6/0x750 net/socket.c:1276
sock_create net/socket.c:1316 [inline]
__sys_socket+0x103/0x220 net/socket.c:1346
__do_sys_socket net/socket.c:1355 [inline]
__se_sys_socket net/socket.c:1353 [inline]
__x64_sys_socket+0x73/0xb0 net/socket.c:1353
do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 11324:
save_stack+0x45/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/kasan.c:521
kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
__cache_free mm/slab.c:3503 [inline]
kfree+0xcf/0x230 mm/slab.c:3822
sk_prot_free net/core/sock.c:1506 [inline]
__sk_destruct+0x4f1/0x6d0 net/core/sock.c:1588
sk_destruct+0x7b/0x90 net/core/sock.c:1596
__sk_free+0xce/0x300 net/core/sock.c:1607
sk_free+0x42/0x50 net/core/sock.c:1618
sock_put include/net/sock.h:1702 [inline]
nr_release+0x337/0x3c0 net/netrom/af_netrom.c:557
__sock_release+0xd3/0x2b0 net/socket.c:579
sock_close+0x1b/0x30 net/socket.c:1140
__fput+0x2df/0x8b0 fs/file_table.c:278
____fput+0x16/0x20 fs/file_table.c:309
task_work_run+0x14a/0x1c0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:193 [inline]
exit_to_usermode_loop+0x273/0x2c0 arch/x86/entry/common.c:166
prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
do_syscall_64+0x52d/0x610 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8880a13ed140
which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 128 bytes inside of
2048-byte region [ffff8880a13ed140, ffff8880a13ed940)
The buggy address belongs to the page:
page:ffffea000284fb00 count:1 mapcount:0 mapping:ffff88812c3f0c40 index:0x0
compound_mapcount: 0
flags: 0x1fffc0000008100(slab|head)
raw: 01fffc0000008100 ffffea000270a088 ffffea000284b588 ffff88812c3f0c40
raw: 0000000000000000 ffff8880a13ec040 0000000100000003 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8880a13ed080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8880a13ed100: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
> ffff8880a13ed180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8880a13ed200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880a13ed280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.