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SubjectKASAN: use-after-free Read in refcount_inc_not_zero_checked
From
Hello,

syzbot found the following crash on:

HEAD commit: 6a1d293238c1 Add linux-next specific files for 20181224
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=100ff080c00000
kernel config: https://syzkaller.appspot.com/x/.config?x=af046212050aa3ac
dashboard link: https://syzkaller.appspot.com/bug?extid=defa700d16f1bd1b9a05
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+defa700d16f1bd1b9a05@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in atomic_read
include/generated/atomic-instrumented.h:26 [inline]
BUG: KASAN: use-after-free in refcount_inc_not_zero_checked+0x90/0x2c0
lib/refcount.c:120
Read of size 4 at addr ffff8880576b03c0 by task syz-executor0/12972

CPU: 1 PID: 12972 Comm: syz-executor0 Not tainted 4.20.0-rc7-next-20181224
#1
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+0x1db/0x2d0 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:100
atomic_read include/generated/atomic-instrumented.h:26 [inline]
refcount_inc_not_zero_checked+0x90/0x2c0 lib/refcount.c:120
refcount_inc_checked+0x17/0x70 lib/refcount.c:153
sock_hold include/net/sock.h:643 [inline]
nr_release+0x62/0x3c0 net/netrom/af_netrom.c:523
__sock_release+0xd3/0x250 net/socket.c:579
sock_close+0x1b/0x30 net/socket.c:1141
__fput+0x3cd/0xaa0 fs/file_table.c:279
____fput+0x16/0x20 fs/file_table.c:312
task_work_run+0x1f4/0x2b0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:188 [inline]
exit_to_usermode_loop+0x32a/0x3b0 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+0x696/0x800 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x411c91
Code: 75 14 b8 03 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 94 19 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:00007fff4f364100 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000005 RCX: 0000000000411c91
RDX: 0000000000000000 RSI: 000000000000123b RDI: 0000000000000004
RBP: 0000000000000000 R08: 000000003436323b R09: 000000003436323f
R10: 00007fff4f364030 R11: 0000000000000293 R12: 0000000000000000
R13: 0000000000000001 R14: 00000000000014d3 R15: 0000000000000000

Allocated by task 12976:
save_stack+0x45/0xd0 mm/kasan/common.c:73
set_track mm/kasan/common.c:85 [inline]
kasan_kmalloc mm/kasan/common.c:482 [inline]
kasan_kmalloc+0xcf/0xe0 mm/kasan/common.c:455
__do_kmalloc mm/slab.c:3709 [inline]
__kmalloc+0x15c/0x740 mm/slab.c:3718
kmalloc include/linux/slab.h:550 [inline]
sk_prot_alloc+0x19c/0x2e0 net/core/sock.c:1477
sk_alloc+0xd7/0x1690 net/core/sock.c:1531
nr_create+0xb9/0x5e0 net/netrom/af_netrom.c:436
__sock_create+0x532/0x930 net/socket.c:1277
sock_create net/socket.c:1317 [inline]
__sys_socket+0x106/0x260 net/socket.c:1347
__do_sys_socket net/socket.c:1356 [inline]
__se_sys_socket net/socket.c:1354 [inline]
__x64_sys_socket+0x73/0xb0 net/socket.c:1354
do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 12972:
save_stack+0x45/0xd0 mm/kasan/common.c:73
set_track mm/kasan/common.c:85 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/common.c:444
kasan_slab_free+0xe/0x10 mm/kasan/common.c:452
__cache_free mm/slab.c:3485 [inline]
kfree+0xcf/0x230 mm/slab.c:3804
sk_prot_free net/core/sock.c:1514 [inline]
__sk_destruct+0x76d/0xa60 net/core/sock.c:1596
sk_destruct+0x7b/0x90 net/core/sock.c:1604
__sk_free+0xce/0x300 net/core/sock.c:1615
sk_free+0x42/0x50 net/core/sock.c:1626
sock_put include/net/sock.h:1703 [inline]
nr_release+0x337/0x3c0 net/netrom/af_netrom.c:557
__sock_release+0xd3/0x250 net/socket.c:579
sock_close+0x1b/0x30 net/socket.c:1141
__fput+0x3cd/0xaa0 fs/file_table.c:279
____fput+0x16/0x20 fs/file_table.c:312
task_work_run+0x1f4/0x2b0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:188 [inline]
exit_to_usermode_loop+0x32a/0x3b0 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+0x696/0x800 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8880576b0340
which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 128 bytes inside of
2048-byte region [ffff8880576b0340, ffff8880576b0b40)
The buggy address belongs to the page:
page:ffffea00015dac00 count:1 mapcount:0 mapping:ffff88812c3f0c40 index:0x0
compound_mapcount: 0
flags: 0x1fffc0000010200(slab|head)
raw: 01fffc0000010200 ffffea000237cc88 ffffea0002528808 ffff88812c3f0c40
raw: 0000000000000000 ffff8880576b0340 0000000100000003 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8880576b0280: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8880576b0300: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
> ffff8880576b0380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8880576b0400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880576b0480: 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.

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