KASAN: use-after-free Read in l2cap_chan

KASAN: use-after-free Read in l2cap_chan_close
Status: upstream: reported C repro on 2020/02/07 17:18
Reported-by: syzbot+96414aa0033c363d8458@syzkaller.appspotmail.com
First crash: 9d20h, last: 8d10h

Cause bisection: the bug happens on the oldest tested release
Crash: WARNING in sysfs_warn_dup (log)
Repro: C syz .config

similar bugs (2):
Kernel	Title	Repro	Bisected	Count	Last	Reported	Patched	Status
linux-4.14	KASAN: use-after-free Read in l2cap_chan_close	C		1	9d06h	9d06h	0/1	upstream: reported C repro on 2020/02/08 02:54
linux-4.19	KASAN: use-after-free Read in l2cap_chan_close	C		1	10d	10d	0/1	upstream: reported C repro on 2020/02/06 18:16

Sample crash report:

==================================================================
BUG: KASAN: use-after-free in l2cap_chan_close+0x661/0xa10 net/bluetooth/l2cap_core.c:734
Read of size 1 at addr ffff88808abbf020 by task kworker/0:1/9817

CPU: 0 PID: 9817 Comm: kworker/0:1 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+0x197/0x210 lib/dump_stack.c:118
 print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
 __kasan_report.cold+0x1b/0x32 mm/kasan/report.c:506
 kasan_report+0x12/0x20 mm/kasan/common.c:641
 __asan_report_load1_noabort+0x14/0x20 mm/kasan/generic_report.c:132
 l2cap_chan_close+0x661/0xa10 net/bluetooth/l2cap_core.c:734
 do_enable_set+0x53f/0x960 net/bluetooth/6lowpan.c:1074
 process_one_work+0xa05/0x17a0 kernel/workqueue.c:2264
 worker_thread+0x98/0xe40 kernel/workqueue.c:2410
 kthread+0x361/0x430 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Allocated by task 9817:
 save_stack+0x23/0x90 mm/kasan/common.c:72
 set_track mm/kasan/common.c:80 [inline]
 __kasan_kmalloc mm/kasan/common.c:515 [inline]
 __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:488
 kasan_kmalloc+0x9/0x10 mm/kasan/common.c:529
 kmem_cache_alloc_trace+0x158/0x790 mm/slab.c:3551
 kmalloc include/linux/slab.h:555 [inline]
 kzalloc include/linux/slab.h:669 [inline]
 l2cap_chan_create+0x45/0x3a0 net/bluetooth/l2cap_core.c:446
 chan_create+0x10/0xe0 net/bluetooth/6lowpan.c:640
 bt_6lowpan_listen net/bluetooth/6lowpan.c:959 [inline]
 do_enable_set+0x583/0x960 net/bluetooth/6lowpan.c:1078
 process_one_work+0xa05/0x17a0 kernel/workqueue.c:2264
 worker_thread+0x98/0xe40 kernel/workqueue.c:2410
 kthread+0x361/0x430 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Freed by task 3100:
 save_stack+0x23/0x90 mm/kasan/common.c:72
 set_track mm/kasan/common.c:80 [inline]
 kasan_set_free_info mm/kasan/common.c:337 [inline]
 __kasan_slab_free+0x102/0x150 mm/kasan/common.c:476
 kasan_slab_free+0xe/0x10 mm/kasan/common.c:485
 __cache_free mm/slab.c:3426 [inline]
 kfree+0x10a/0x2c0 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+0x1b7/0x240 net/bluetooth/l2cap_core.c:498
 do_enable_set+0x54b/0x960 net/bluetooth/6lowpan.c:1075
 process_one_work+0xa05/0x17a0 kernel/workqueue.c:2264
 worker_thread+0x98/0xe40 kernel/workqueue.c:2410
 kthread+0x361/0x430 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

The buggy address belongs to the object at ffff88808abbf000
 which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 32 bytes inside of
 2048-byte region [ffff88808abbf000, ffff88808abbf800)
The buggy address belongs to the page:
page:ffffea00022aefc0 refcount:1 mapcount:0 mapping:ffff8880aa400e00 index:0x0
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea00024aea88 ffffea000250c1c8 ffff8880aa400e00
raw: 0000000000000000 ffff88808abbf000 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88808abbef00: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
 ffff88808abbef80: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
>ffff88808abbf000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                               ^
 ffff88808abbf080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88808abbf100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (3):
Manager	Time	Kernel	Commit	Syzkaller	Config	Log	Report	Syz repro	C repro	Maintainers
ci-upstream-kasan-gce-root	2020/02/08 23:02	upstream	f7571657	06150bf1	.config	log	report	syz	C	davem@davemloft.net, johan.hedberg@gmail.com, kuba@kernel.org, linux-bluetooth@vger.kernel.org, linux-kernel@vger.kernel.org, marcel@holtmann.org, netdev@vger.kernel.org
ci-upstream-kasan-gce	2020/02/08 05:17	upstream	41dcd67e	06150bf1	.config	log	report	syz	C	davem@davemloft.net, johan.hedberg@gmail.com, kuba@kernel.org, linux-bluetooth@vger.kernel.org, linux-kernel@vger.kernel.org, marcel@holtmann.org, netdev@vger.kernel.org
ci-upstream-kasan-gce-smack-root	2020/02/07 12:55	upstream	90568ecf	06150bf1	.config	log	report	syz	C	davem@davemloft.net, johan.hedberg@gmail.com, kuba@kernel.org, linux-bluetooth@vger.kernel.org, linux-kernel@vger.kernel.org, marcel@holtmann.org, netdev@vger.kernel.org