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SubjectKASAN: use-after-free Read in refcount_inc_not_zero_checked (2)
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Hello,

syzbot found the following crash on:

HEAD commit: 9c7dc824 Merge tag '5.1-rc-smb3' of git://git.samba.org/sf..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=170ae6d7200000
kernel config: https://syzkaller.appspot.com/x/.config?x=7e1aaa1cfbfe1abf
dashboard link: https://syzkaller.appspot.com/bug?extid=eff6b596cc8194e2f029
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17e294a3200000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+eff6b596cc8194e2f029@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in atomic_read
include/asm-generic/atomic-instrumented.h:26 [inline]
BUG: KASAN: use-after-free in refcount_inc_not_zero_checked+0x81/0x200
lib/refcount.c:123
Read of size 4 at addr ffff8880a614c280 by task syz-executor.3/7636

CPU: 1 PID: 7636 Comm: syz-executor.3 Not tainted 5.0.0+ #25
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:187
kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317
check_memory_region_inline mm/kasan/generic.c:185 [inline]
check_memory_region+0x123/0x190 mm/kasan/generic.c:191
kasan_check_read+0x11/0x20 mm/kasan/common.c:102
atomic_read include/asm-generic/atomic-instrumented.h:26 [inline]
refcount_inc_not_zero_checked+0x81/0x200 lib/refcount.c:123
refcount_inc_checked+0x17/0x70 lib/refcount.c:156
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:1162
__fput+0x2e5/0x8d0 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:188 [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: 0033:0x411e31
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:00007ffcf55d0f50 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000007 RCX: 0000000000411e31
RDX: 0000000000000000 RSI: 00000000007410c8 RDI: 0000000000000006
RBP: 0000000000000000 R08: 000000000002cf1a R09: 000000000002cf1a
R10: 00007ffcf55d0e80 R11: 0000000000000293 R12: 0000000000000001
R13: 00007ffcf55d0f90 R14: 0000000000000000 R15: 00007ffcf55d0fa0

Allocated by task 7638:
save_stack+0x45/0xd0 mm/kasan/common.c:75
set_track mm/kasan/common.c:87 [inline]
__kasan_kmalloc mm/kasan/common.c:497 [inline]
__kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:470
kasan_kmalloc+0x9/0x10 mm/kasan/common.c:511
__do_kmalloc mm/slab.c:3726 [inline]
__kmalloc+0x15c/0x740 mm/slab.c:3735
kmalloc include/linux/slab.h:550 [inline]
sk_prot_alloc+0x19c/0x2e0 net/core/sock.c:1607
sk_alloc+0x39/0xf70 net/core/sock.c:1661
nr_create+0xb9/0x5e0 net/netrom/af_netrom.c:436
__sock_create+0x3e6/0x750 net/socket.c:1298
sock_create net/socket.c:1338 [inline]
__sys_socket+0x103/0x220 net/socket.c:1368
__do_sys_socket net/socket.c:1377 [inline]
__se_sys_socket net/socket.c:1375 [inline]
__x64_sys_socket+0x73/0xb0 net/socket.c:1375
do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 7636:
save_stack+0x45/0xd0 mm/kasan/common.c:75
set_track mm/kasan/common.c:87 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/common.c:459
kasan_slab_free+0xe/0x10 mm/kasan/common.c:467
__cache_free mm/slab.c:3498 [inline]
kfree+0xcf/0x230 mm/slab.c:3821
sk_prot_free net/core/sock.c:1644 [inline]
__sk_destruct+0x4f1/0x6d0 net/core/sock.c:1726
sk_destruct+0x7b/0x90 net/core/sock.c:1734
__sk_free+0xce/0x300 net/core/sock.c:1745
sk_free+0x42/0x50 net/core/sock.c:1756
sock_put include/net/sock.h:1708 [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:1162
__fput+0x2e5/0x8d0 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:188 [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 ffff8880a614c200
which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 128 bytes inside of
2048-byte region [ffff8880a614c200, ffff8880a614ca00)
The buggy address belongs to the page:
page:ffffea0002985300 count:1 mapcount:0 mapping:ffff88812c3f0c40 index:0x0
compound_mapcount: 0
flags: 0x1fffc0000010200(slab|head)
raw: 01fffc0000010200 ffffea00022f4408 ffffea000218f408 ffff88812c3f0c40
raw: 0000000000000000 ffff8880a614c200 0000000100000003 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8880a614c180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8880a614c200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff8880a614c280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8880a614c300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880a614c380: 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 syzkaller@googlegroups.com.

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syzbot.
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

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