Subject: KASAN: use-after-free Read in l2cap_chan_close

From: syzbot <[email-masked]>
Date: Fri, 07 Feb 2020 09:18:12 -0800

Hello,

syzbot found the following crash on:

HEAD commit:    90568ecf Merge tag 'kvm-5.6-2' of git://git.kernel.org/pub..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16fe894ee00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=69fa012479f9a62
dashboard link: https://syzkaller.appspot.com/bug?extid=96414aa0033c363d8458
compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=142dd4e9e00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=102c37f1e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: [email-masked]

==================================================================
BUG: KASAN: use-after-free in l2cap_chan_close+0x48/0x990 net/bluetooth/l2cap_core.c:730
Read of size 8 at addr ffff888096950000 by task kworker/1:102/2868

CPU: 1 PID: 2868 Comm: kworker/1:102 Not tainted 5.5.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events do_enable_set
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1fb/0x318 lib/dump_stack.c:118
 print_address_description+0x74/0x5c0 mm/kasan/report.c:374
 __kasan_report+0x149/0x1c0 mm/kasan/report.c:506
 kasan_report+0x26/0x50 mm/kasan/common.c:641
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:135
 l2cap_chan_close+0x48/0x990 net/bluetooth/l2cap_core.c:730
 do_enable_set+0x660/0x900 net/bluetooth/6lowpan.c:1074
 process_one_work+0x7f5/0x10f0 kernel/workqueue.c:2264
 worker_thread+0xbbc/0x1630 kernel/workqueue.c:2410
 kthread+0x332/0x350 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Allocated by task 2870:
 save_stack mm/kasan/common.c:72 [inline]
 set_track mm/kasan/common.c:80 [inline]
 __kasan_kmalloc+0x118/0x1c0 mm/kasan/common.c:515
 kasan_kmalloc+0x9/0x10 mm/kasan/common.c:529
 kmem_cache_alloc_trace+0x221/0x2f0 mm/slab.c:3551
 kmalloc include/linux/slab.h:555 [inline]
 kzalloc include/linux/slab.h:669 [inline]
 l2cap_chan_create+0x50/0x320 net/bluetooth/l2cap_core.c:446
 chan_create net/bluetooth/6lowpan.c:640 [inline]
 bt_6lowpan_listen net/bluetooth/6lowpan.c:959 [inline]
 do_enable_set+0x6a4/0x900 net/bluetooth/6lowpan.c:1078
 process_one_work+0x7f5/0x10f0 kernel/workqueue.c:2264
 worker_thread+0xbbc/0x1630 kernel/workqueue.c:2410
 kthread+0x332/0x350 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Freed by task 2870:
 save_stack mm/kasan/common.c:72 [inline]
 set_track mm/kasan/common.c:80 [inline]
 kasan_set_free_info mm/kasan/common.c:337 [inline]
 __kasan_slab_free+0x12e/0x1e0 mm/kasan/common.c:476
 kasan_slab_free+0xe/0x10 mm/kasan/common.c:485
 __cache_free mm/slab.c:3426 [inline]
 kfree+0x10d/0x220 mm/slab.c:3757
 l2cap_chan_destroy net/bluetooth/l2cap_core.c:484 [inline]
 kref_put include/linux/kref.h:65 [inline]
 l2cap_chan_put+0x170/0x190 net/bluetooth/l2cap_core.c:498
 do_enable_set+0x66c/0x900 net/bluetooth/6lowpan.c:1075
 process_one_work+0x7f5/0x10f0 kernel/workqueue.c:2264
 worker_thread+0xbbc/0x1630 kernel/workqueue.c:2410
 kthread+0x332/0x350 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

The buggy address belongs to the object at ffff888096950000
 which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 0 bytes inside of
 2048-byte region [ffff888096950000, ffff888096950800)
The buggy address belongs to the page:
page:ffffea00025a5400 refcount:1 mapcount:0 mapping:ffff8880aa400e00 index:0x0
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea00027d1548 ffffea0002397808 ffff8880aa400e00
raw: 0000000000000000 ffff888096950000 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88809694ff00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff88809694ff80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff888096950000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff888096950080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888096950100: 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 [email-masked].

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches