[PATCH] Bluetooth: A2MP: fix slab-use-after-free in l2cap_chan_del
From: Sungwoo Kim
Date: Fri Apr 26 2024 - 04:31:59 EST
l2cap_set_timer() may potentially dereference chan->conn->hcon->amp_mgr.
However, the timer does not hold amp_mgr, allowing uaf as follows:
l2cap_set_timer()
l2cap_chan_timeout()
l2cap_chan_close()
l2cap_chan_del()
if (mgr && mgr->bredr_chan == chan) // uaf at mgr->bredr_chan
One patch could be calling amp_mgr_get(chan->conn->hcon->amp_mgr) in l2cap_set_timer().
This will increase refcnt and make mgr alive at l2cap_chan_del().
Unfortunately, amp_mgr_get() is in a2mp.h and l2cap_set_timer() is in l2cap.h.
Including a2mp.h in l2cap.h makes circular (and dirty "../../net/bluetooth/a2mp.h")
dependency because a2mp.h already includes l2cap.h.
So.. as a temporary work, this patch assigns NULL to conn->amp_mgr.
While this makes it less likely to trigger the bug, the bug still can
happen because mgr && mgr->bredr is not atomic.
Could we talk about a better idea?
Also, AMP is removed recently.
The kernel with versions <= v6.8 might have this issue.
==================================================================
BUG: KASAN: slab-use-after-free in l2cap_chan_del+0x31d/0x6b0 net/bluetooth/l2cap_core.c:670
Read of size 8 at addr ffff88810dab7220 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_chan_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_load8_noabort+0x18/0x20 mm/kasan/report_generic.c:381
l2cap_chan_del+0x31d/0x6b0 net/bluetooth/l2cap_core.c:670
l2cap_chan_close+0x53c/0x930
l2cap_chan_timeout+0x10b/0x300 net/bluetooth/l2cap_core.c:452
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 296:
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]
kmalloc_trace+0x1c9/0x390 mm/slub.c:4012
kmalloc include/linux/slab.h:590 [inline]
kzalloc include/linux/slab.h:711 [inline]
amp_mgr_create+0x5d/0xd30 net/bluetooth/a2mp.c:854
a2mp_channel_create+0x60/0x110 net/bluetooth/a2mp.c:894
l2cap_data_channel net/bluetooth/l2cap_core.c:7676 [inline]
l2cap_recv_frame+0xbd7/0x86a0 net/bluetooth/l2cap_core.c:7832
l2cap_recv_acldata+0x379/0xbe0 net/bluetooth/l2cap_core.c:8536
hci_acldata_packet net/bluetooth/hci_core.c:3876 [inline]
hci_rx_work+0x64b/0xcb0 net/bluetooth/hci_core.c:4111
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
Freed by task 296:
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
amp_mgr_destroy net/bluetooth/a2mp.c:839 [inline]
kref_put include/linux/kref.h:65 [inline]
amp_mgr_put+0x16b/0x230 net/bluetooth/a2mp.c:846
hci_conn_del+0x39d/0xc30 net/bluetooth/hci_conn.c:1179
hci_phy_link_complete_evt+0x135/0x3d0 net/bluetooth/hci_event.c:5713
hci_event_func net/bluetooth/hci_event.c:7689 [inline]
hci_event_packet+0x8e9/0x1290 net/bluetooth/hci_event.c:7741
hci_rx_work+0x387/0xcb0 net/bluetooth/hci_core.c:4106
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
The buggy address belongs to the object at ffff88810dab7200
which belongs to the cache kmalloc-128 of size 128
The buggy address is located 32 bytes inside of
freed 128-byte region [ffff88810dab7200, ffff88810dab7280)
The buggy address belongs to the physical page:
page:00000000a802fdc8 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff88810dab7200 pfn:0x10dab7
flags: 0x17ffffc0000a00(workingset|slab|node=0|zone=2|lastcpupid=0x1fffff)
page_type: 0xffffffff()
raw: 0017ffffc0000a00 ffff8881000418c0 ffffea000410d710 ffffea00041c6e90
raw: ffff88810dab7200 000000000010000f 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
Memory state around the buggy address:
ffff88810dab7100: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88810dab7180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88810dab7200: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88810dab7280: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88810dab7300: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================
Signed-off-by: Sungwoo Kim <iam@xxxxxxxxxxxx>
---
net/bluetooth/hci_conn.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
index a41d2693f..f9b41add1 100644
--- a/net/bluetooth/hci_conn.c
+++ b/net/bluetooth/hci_conn.c
@@ -1175,8 +1175,10 @@ void hci_conn_del(struct hci_conn *conn)
}
}
- if (conn->amp_mgr)
+ if (conn->amp_mgr) {
amp_mgr_put(conn->amp_mgr);
+ conn->amp_mgr = NULL;
+ }
skb_queue_purge(&conn->data_q);
--
2.34.1