Hello, could you review a bug and its fix?
This is a racy bug. Call stack is as below:
[free]
l2cap_conn_del
┌ mutex_lock(&conn->chan_lock);
│ foreach chan in conn->chan_l: ... (2)
│ l2cap_chan_put(chan);
│ l2cap_chan_destroy
│ kfree(chan) ... (3)
└ mutex_unlock(&conn->chan_lock);
[use]
l2cap_bredr_sig_cmd
l2cap_connect
┌ mutex_lock(&conn->chan_lock);
│ chan = pchan->ops->new_connection(pchan); // alloc chan
│ __l2cap_chan_add(conn, chan);
│ l2cap_chan_hold(chan);
│ list_add(&chan->list, &conn->chan_l); ... (1)
└ mutex_unlock(&conn->chan_lock);
chan->conf_state // uaf at chan ... (4)
To fix this, this patch holds and locks the l2cap channel.
Thanks,
Sungwoo.
==================================================================
BUG: KASAN: slab-use-after-free in l2cap_send_cmd+0x5dc/0x830 net/bluetooth/l2cap_core.c:968
Read of size 1 at addr ffff88810b62c274 by task kworker/0:1/10
CPU: 0 PID: 10 Comm: kworker/0:1 Not tainted 6.8.0+ #61
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
Workqueue: events l2cap_info_timeout
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x85/0xb0 lib/dump_stack.c:106
print_address_description mm/kasan/report.c:377 [inline]
print_report+0x18f/0x560 mm/kasan/report.c:488
kasan_report+0xd7/0x110 mm/kasan/report.c:601
__asan_report_load1_noabort+0x18/0x20 mm/kasan/report_generic.c:378
l2cap_send_cmd+0x5dc/0x830 net/bluetooth/l2cap_core.c:968
l2cap_send_conn_req net/bluetooth/l2cap_core.c:1286 [inline]
l2cap_start_connection+0x25e/0x530 net/bluetooth/l2cap_core.c:1514
l2cap_conn_start+0x952/0xe60 net/bluetooth/l2cap_core.c:1661
l2cap_info_timeout+0x5f/0x90 net/bluetooth/l2cap_core.c:1807
process_one_work kernel/workqueue.c:2633 [inline]
process_scheduled_works+0x6b9/0xdc0 kernel/workqueue.c:2706
worker_thread+0xb2b/0x13d0 kernel/workqueue.c:2787
kthread+0x2a9/0x340 kernel/kthread.c:388
ret_from_fork+0x5c/0x90 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1b/0x30 arch/x86/entry/entry_64.S:243
</TASK>
Allocated by task 290:
kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_save_track+0x30/0x70 mm/kasan/common.c:68
kasan_save_alloc_info+0x3c/0x50 mm/kasan/generic.c:575
poison_kmalloc_redzone mm/kasan/common.c:370 [inline]
__kasan_kmalloc+0xa2/0xc0 mm/kasan/common.c:387
kasan_kmalloc include/linux/kasan.h:211 [inline]
__do_kmalloc_node mm/slub.c:3981 [inline]
__kmalloc+0x228/0x4d0 mm/slub.c:3994
kmalloc include/linux/slab.h:594 [inline]
kzalloc include/linux/slab.h:711 [inline]
hci_alloc_dev_priv+0x30/0x1ea0 net/bluetooth/hci_core.c:2468
hci_alloc_dev include/net/bluetooth/hci_core.h:1651 [inline]
__vhci_create_device drivers/bluetooth/hci_vhci.c:406 [inline]
vhci_create_device+0x10e/0x710 drivers/bluetooth/hci_vhci.c:480
vhci_get_user drivers/bluetooth/hci_vhci.c:537 [inline]
vhci_write+0x398/0x460 drivers/bluetooth/hci_vhci.c:617
call_write_iter include/linux/fs.h:2087 [inline]
new_sync_write fs/read_write.c:497 [inline]
vfs_write+0x9ee/0xd40 fs/read_write.c:590
ksys_write+0x103/0x1f0 fs/read_write.c:643
__do_sys_write fs/read_write.c:655 [inline]
__se_sys_write fs/read_write.c:652 [inline]
__x64_sys_write+0x84/0xa0 fs/read_write.c:652
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0x84/0x120 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x6e/0x76
Freed by task 1158:
kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_save_track+0x30/0x70 mm/kasan/common.c:68
kasan_save_free_info+0x44/0x50 mm/kasan/generic.c:589
poison_slab_object+0x11a/0x190 mm/kasan/common.c:240
__kasan_slab_free+0x3b/0x60 mm/kasan/common.c:256
kasan_slab_free include/linux/kasan.h:184 [inline]
slab_free_hook mm/slub.c:2121 [inline]
slab_free mm/slub.c:4299 [inline]
kfree+0x106/0x2e0 mm/slub.c:4409
hci_release_dev+0x1114/0x1250 net/bluetooth/hci_core.c:2799
bt_host_release+0x77/0x90 net/bluetooth/hci_sysfs.c:94
device_release+0xa4/0x1d0
kobject_cleanup lib/kobject.c:689 [inline]
kobject_release lib/kobject.c:720 [inline]
kref_put include/linux/kref.h:65 [inline]
kobject_put+0x1f1/0x410 lib/kobject.c:737
put_device+0x28/0x40 drivers/base/core.c:3747
hci_free_dev+0x25/0x30 net/bluetooth/hci_core.c:2594
vhci_release+0x91/0xe0 drivers/bluetooth/hci_vhci.c:675
__fput+0x35b/0x740 fs/file_table.c:376
____fput+0x1e/0x30 fs/file_table.c:404
task_work_run+0x1d9/0x270 kernel/task_work.c:180
exit_task_work include/linux/task_work.h:38 [inline]
do_exit+0x823/0x23e0 kernel/exit.c:871
do_group_exit+0x1f1/0x2b0 kernel/exit.c:1020
get_signal+0x1387/0x14d0 kernel/signal.c:2893
arch_do_signal_or_restart+0x3b/0x650 arch/x86/kernel/signal.c:310
exit_to_user_mode_loop kernel/entry/common.c:105 [inline]
exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
__syscall_exit_to_user_mode_work kernel/entry/common.c:201 [inline]
syscall_exit_to_user_mode+0x71/0x180 kernel/entry/common.c:212
do_syscall_64+0x90/0x120 arch/x86/entry/common.c:89
entry_SYSCALL_64_after_hwframe+0x6e/0x76
Last potentially related work creation:
kasan_save_stack+0x2f/0x50 mm/kasan/common.c:47
__kasan_record_aux_stack+0xc6/0xe0 mm/kasan/generic.c:551
kasan_record_aux_stack_noalloc+0xf/0x20 mm/kasan/generic.c:561
insert_work+0x3a/0x1d0 kernel/workqueue.c:1653
__queue_work+0xa5b/0xdc0 kernel/workqueue.c:1806
queue_work_on+0x74/0xa0 kernel/workqueue.c:1837
queue_work include/linux/workqueue.h:548 [inline]
hci_recv_frame+0x375/0x490 net/bluetooth/hci_core.c:2947
hci_reset_dev+0x126/0x170 net/bluetooth/hci_core.c:2904
hci_ncmd_timeout+0xb1/0xd0 net/bluetooth/hci_core.c:1525
process_one_work kernel/workqueue.c:2633 [inline]
process_scheduled_works+0x6b9/0xdc0 kernel/workqueue.c:2706
worker_thread+0xb2b/0x13d0 kernel/workqueue.c:2787
kthread+0x2a9/0x340 kernel/kthread.c:388
ret_from_fork+0x5c/0x90 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1b/0x30 arch/x86/entry/entry_64.S:243
Second to last potentially related work creation:
kasan_save_stack+0x2f/0x50 mm/kasan/common.c:47
__kasan_record_aux_stack+0xc6/0xe0 mm/kasan/generic.c:551
kasan_record_aux_stack_noalloc+0xf/0x20 mm/kasan/generic.c:561
insert_work kernel/workqueue.c:1653 [inline]
__queue_work+0x8cf/0xdc0 kernel/workqueue.c:1802
delayed_work_timer_fn+0x6a/0x90 kernel/workqueue.c:1931
call_timer_fn+0x44/0x240 kernel/time/timer.c:1700
expire_timers kernel/time/timer.c:1746 [inline]
__run_timers+0x63a/0x870 kernel/time/timer.c:2038
run_timer_softirq+0x26/0x40 kernel/time/timer.c:2051
__do_softirq+0x180/0x523 kernel/softirq.c:553
The buggy address belongs to the object at ffff88810b62c000
which belongs to the cache kmalloc-8k of size 8192
The buggy address is located 628 bytes inside of
freed 8192-byte region [ffff88810b62c000, ffff88810b62e000)
The buggy address belongs to the physical page:
page:000000007f8eb4fe refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10b628
head:000000007f8eb4fe order:3 entire_mapcount:0 nr_pages_mapped:0 pincount:0
anon flags: 0x17ffffc0000840(slab|head|node=0|zone=2|lastcpupid=0x1fffff)
page_type: 0xffffffff()
raw: 0017ffffc0000840 ffff888100042280 0000000000000000 0000000000000001
raw: 0000000000000000 0000000000020002 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
Memory state around the buggy address:
ffff88810b62c100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88810b62c180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88810b62c200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88810b62c280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88810b62c300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
Signed-off-by: Sungwoo Kim <iam@xxxxxxxxxxxx>
---
net/bluetooth/l2cap_core.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 84fc70862..a8f414ab8 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -3953,6 +3953,9 @@ static struct l2cap_chan *l2cap_connect(struct l2cap_conn *conn,
if (!chan)
goto response;
+ l2cap_chan_hold(chan);
+ l2cap_chan_lock(chan);
+
/* For certain devices (ex: HID mouse), support for authentication,
* pairing and bonding is optional. For such devices, inorder to avoid
* the ACL alive for too long after L2CAP disconnection, reset the ACL
@@ -4041,6 +4044,11 @@ static struct l2cap_chan *l2cap_connect(struct l2cap_conn *conn,
chan->num_conf_req++;
}
+ if (chan) {
+ l2cap_chan_unlock(chan);
+ l2cap_chan_put(chan);
+ }
+
return chan;
}
--
2.34.1
