KASAN: use-after-free Read in l2cap_chan

KASAN: use-after-free Read in l2cap_chan_close
Status: upstream: reported C repro on 2020/02/08 02:54
Reported-by: syzbot+b70b68318b213bb8c149@syzkaller.appspotmail.com
First crash: 389d, last: 206d

Fix bisection: the fix commit could be any of (bisect log):
ab9dfda23248 Linux 4.14.180
56dfe6252c68 Linux 4.14.188

similar bugs (2):
Kernel	Title	Repro	Cause bisect	Fix bisect	Count	Last	Reported	Patched	Status
linux-4.19	KASAN: use-after-free Read in l2cap_chan_close	C		done	8	208d	391d	1/1	fixed on 2020/09/09 05:22
upstream	KASAN: use-after-free Read in l2cap_chan_close	C	done		37	209d	390d	17/21	fixed on 2020/09/16 22:51

Sample crash report:

audit: type=1400 audit(1596913669.871:8): avc:  denied  { execmem } for  pid=6358 comm="syz-executor973" scontext=system_u:system_r:kernel_t:s0 tcontext=system_u:system_r:kernel_t:s0 tclass=process permissive=1
==================================================================
BUG: KASAN: use-after-free in l2cap_chan_close+0x4fb/0x770 net/bluetooth/l2cap_core.c:727
Read of size 1 at addr ffff8880976a24e0 by task kworker/1:2/3653

CPU: 1 PID: 3653 Comm: kworker/1:2 Not tainted 4.14.193-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:17 [inline]
 dump_stack+0x1b2/0x283 lib/dump_stack.c:58
 print_address_description.cold+0x54/0x1d3 mm/kasan/report.c:252
 kasan_report_error.cold+0x8a/0x194 mm/kasan/report.c:351
 kasan_report mm/kasan/report.c:409 [inline]
 __asan_report_load1_noabort+0x68/0x70 mm/kasan/report.c:427
 l2cap_chan_close+0x4fb/0x770 net/bluetooth/l2cap_core.c:727
 do_enable_set+0x473/0x8a0 net/bluetooth/6lowpan.c:1086
 process_one_work+0x793/0x14a0 kernel/workqueue.c:2116
 worker_thread+0x5cc/0xff0 kernel/workqueue.c:2250
 kthread+0x30d/0x420 kernel/kthread.c:232
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:404

Allocated by task 24:
 save_stack mm/kasan/kasan.c:447 [inline]
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc+0xeb/0x160 mm/kasan/kasan.c:551
 kmem_cache_alloc_trace+0x131/0x3d0 mm/slab.c:3618
 kmalloc include/linux/slab.h:488 [inline]
 kzalloc include/linux/slab.h:661 [inline]
 l2cap_chan_create+0x3e/0x3c0 net/bluetooth/l2cap_core.c:441
 chan_create net/bluetooth/6lowpan.c:652 [inline]
 bt_6lowpan_listen net/bluetooth/6lowpan.c:971 [inline]
 do_enable_set+0x4ac/0x8a0 net/bluetooth/6lowpan.c:1090
 process_one_work+0x793/0x14a0 kernel/workqueue.c:2116
 worker_thread+0x5cc/0xff0 kernel/workqueue.c:2250
 kthread+0x30d/0x420 kernel/kthread.c:232
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:404

Freed by task 24:
 save_stack mm/kasan/kasan.c:447 [inline]
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0xc3/0x1a0 mm/kasan/kasan.c:524
 __cache_free mm/slab.c:3496 [inline]
 kfree+0xc9/0x250 mm/slab.c:3815
 l2cap_chan_destroy net/bluetooth/l2cap_core.c:479 [inline]
 kref_put include/linux/kref.h:70 [inline]
 l2cap_chan_put+0x152/0x1b0 net/bluetooth/l2cap_core.c:493
 do_enable_set+0x47f/0x8a0 net/bluetooth/6lowpan.c:1087
 process_one_work+0x793/0x14a0 kernel/workqueue.c:2116
 worker_thread+0x5cc/0xff0 kernel/workqueue.c:2250
 kthread+0x30d/0x420 kernel/kthread.c:232
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:404

The buggy address belongs to the object at ffff8880976a24c0
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 32 bytes inside of
 2048-byte region [ffff8880976a24c0, ffff8880976a2cc0)
The buggy address belongs to the page:
page:ffffea00025da880 count:1 mapcount:0 mapping:ffff8880976a24c0 index:0x0 compound_mapcount: 0
flags: 0xfffe0000008100(slab|head)
raw: 00fffe0000008100 ffff8880976a24c0 0000000000000000 0000000100000003
raw: ffffea00025d3ca0 ffffea00025c0720 ffff88812fe52c40 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8880976a2380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8880976a2400: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8880976a2480: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
                                                       ^
 ffff8880976a2500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880976a2580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (10):
Manager	Time	Kernel	Commit	Syzkaller	Config	Log	Report	Syz repro	C repro
ci2-linux-4-14	2020/08/08 19:09	linux-4.14.y	14b58326	01975a06	.config	log	report	syz	C
ci2-linux-4-14	2020/08/08 07:42	linux-4.14.y	14b58326	ff51e522	.config	log	report	syz	C
ci2-linux-4-14	2020/08/08 02:25	linux-4.14.y	14b58326	ff51e522	.config	log	report	syz	C
ci2-linux-4-14	2020/08/07 12:18	linux-4.14.y	14b58326	28ac5c9e	.config	log	report	syz	C
ci2-linux-4-14	2020/08/06 05:58	linux-4.14.y	ca4f2c56	0487ea6f	.config	log	report	syz	C
ci2-linux-4-14	2020/08/02 15:25	linux-4.14.y	7f2c5eb4	96dd3623	.config	log	report	syz	C
ci2-linux-4-14	2020/05/18 04:20	linux-4.14.y	ab9dfda2	37bccd4e	.config	log	report	syz	C
ci2-linux-4-14	2020/05/14 14:23	linux-4.14.y	ab9dfda2	2d572622	.config	log	report	syz	C
ci2-linux-4-14	2020/04/23 21:57	linux-4.14.y	c10b57a5	b9233cab	.config	log	report	syz	C
ci2-linux-4-14	2020/02/08 02:53	linux-4.14.y	e0f8b8a6	06150bf1	.config	log	report	syz	C