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

syzbot found the following crash on:

HEAD commit: b71acb0e3721 Merge branch 'linus' of git://git.kernel.org/..
git tree: net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=12227977400000
kernel config: https://syzkaller.appspot.com/x/.config?x=4b137b8ba637eb77
dashboard link: https://syzkaller.appspot.com/bug?extid=b0775615fa4c4479b691
compiler: gcc (GCC) 8.0.1 20180413 (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+b0775615fa4c4479b691@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_sub_and_test_checked+0x9d/0x310
lib/refcount.c:179
Read of size 4 at addr ffff88808c97fec8 by task syz-executor4/9549

CPU: 1 PID: 9549 Comm: syz-executor4 Not tainted 4.20.0+ #363
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+0x1d3/0x2c6 lib/dump_stack.c:113
print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412
check_memory_region_inline mm/kasan/kasan.c:260 [inline]
check_memory_region+0x13e/0x1b0 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_sub_and_test_checked+0x9d/0x310 lib/refcount.c:179
refcount_dec_and_test_checked+0x1a/0x20 lib/refcount.c:212
x25_neigh_put include/net/x25.h:252 [inline]
x25_connect+0xc45/0x1050 net/x25/af_x25.c:823
__sys_connect+0x37d/0x4c0 net/socket.c:1664
__do_sys_connect net/socket.c:1675 [inline]
__se_sys_connect net/socket.c:1672 [inline]
__x64_sys_connect+0x73/0xb0 net/socket.c:1672
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457ec9
Code: 6d b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
ff 0f 83 3b b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f61b98b5c78 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000457ec9
RDX: 0000000000000012 RSI: 0000000020000080 RDI: 0000000000000005
RBP: 000000000073c0e0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f61b98b66d4
R13: 00000000004be405 R14: 00000000004ce5f0 R15: 00000000ffffffff

Allocated by task 5951:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553
kmem_cache_alloc_trace+0x152/0x750 mm/slab.c:3620
kmalloc include/linux/slab.h:546 [inline]
x25_link_device_up+0xb2/0x500 net/x25/x25_link.c:249
x25_device_event+0x116/0x2b0 net/x25/af_x25.c:242
notifier_call_chain+0x17e/0x380 kernel/notifier.c:93
__raw_notifier_call_chain kernel/notifier.c:394 [inline]
raw_notifier_call_chain+0x2d/0x40 kernel/notifier.c:401
call_netdevice_notifiers_info+0x3f/0x90 net/core/dev.c:1739
call_netdevice_notifiers_extack net/core/dev.c:1751 [inline]
call_netdevice_notifiers net/core/dev.c:1765 [inline]
__dev_notify_flags+0x17a/0x480 net/core/dev.c:7605
dev_change_flags+0x109/0x160 net/core/dev.c:7643
dev_ifsioc+0x7da/0xa80 net/core/dev_ioctl.c:237
dev_ioctl+0x1b5/0xcc0 net/core/dev_ioctl.c:488
sock_do_ioctl+0x1f6/0x420 net/socket.c:973
sock_ioctl+0x313/0x690 net/socket.c:1074
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:509 [inline]
do_vfs_ioctl+0x1de/0x1790 fs/ioctl.c:696
ksys_ioctl+0xa9/0xd0 fs/ioctl.c:713
__do_sys_ioctl fs/ioctl.c:720 [inline]
__se_sys_ioctl fs/ioctl.c:718 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 9519:
save_stack+0x43/0xd0 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:3498 [inline]
kfree+0xcf/0x230 mm/slab.c:3817
x25_neigh_put include/net/x25.h:253 [inline]
x25_connect+0xc67/0x1050 net/x25/af_x25.c:823
__sys_connect+0x37d/0x4c0 net/socket.c:1664
__do_sys_connect net/socket.c:1675 [inline]
__se_sys_connect net/socket.c:1672 [inline]
__x64_sys_connect+0x73/0xb0 net/socket.c:1672
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff88808c97fe00
which belongs to the cache kmalloc-256 of size 256
The buggy address is located 200 bytes inside of
256-byte region [ffff88808c97fe00, ffff88808c97ff00)
The buggy address belongs to the page:
page:ffffea0002325fc0 count:1 mapcount:0 mapping:ffff88812c3f07c0
index:0xffff88808c97f2c0
flags: 0x1fffc0000000200(slab)
raw: 01fffc0000000200 ffffea00021df608 ffffea00017f8748 ffff88812c3f07c0
raw: ffff88808c97f2c0 ffff88808c97f040 0000000100000007 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88808c97fd80: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
ffff88808c97fe00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff88808c97fe80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88808c97ff00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88808c97ff80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


---
This bug is generated by a bot. It may contain errors.
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