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Bluetooth: L2CAP: Fix slab-use-after-free Read in l2cap_send_cmd
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After the hci sync command releases l2cap_conn, the hci receive data work
queue references the released l2cap_conn when sending to the upper layer.
Add hci dev lock to the hci receive data work queue to synchronize the two.

[1]
BUG: KASAN: slab-use-after-free in l2cap_send_cmd+0x187/0x8d0 net/bluetooth/l2cap_core.c:954
Read of size 8 at addr ffff8880271a4000 by task kworker/u9:2/5837

CPU: 0 UID: 0 PID: 5837 Comm: kworker/u9:2 Not tainted 6.13.0-rc5-syzkaller-00163-gab75170520d4 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
Workqueue: hci1 hci_rx_work
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0x169/0x550 mm/kasan/report.c:489
 kasan_report+0x143/0x180 mm/kasan/report.c:602
 l2cap_build_cmd net/bluetooth/l2cap_core.c:2964 [inline]
 l2cap_send_cmd+0x187/0x8d0 net/bluetooth/l2cap_core.c:954
 l2cap_sig_send_rej net/bluetooth/l2cap_core.c:5502 [inline]
 l2cap_sig_channel net/bluetooth/l2cap_core.c:5538 [inline]
 l2cap_recv_frame+0x221f/0x10db0 net/bluetooth/l2cap_core.c:6817
 hci_acldata_packet net/bluetooth/hci_core.c:3797 [inline]
 hci_rx_work+0x508/0xdb0 net/bluetooth/hci_core.c:4040
 process_one_work kernel/workqueue.c:3229 [inline]
 process_scheduled_works+0xa66/0x1840 kernel/workqueue.c:3310
 worker_thread+0x870/0xd30 kernel/workqueue.c:3391
 kthread+0x2f0/0x390 kernel/kthread.c:389
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>

Allocated by task 5837:
 kasan_save_stack mm/kasan/common.c:47 [inline]
 kasan_save_track+0x3f/0x80 mm/kasan/common.c:68
 poison_kmalloc_redzone mm/kasan/common.c:377 [inline]
 __kasan_kmalloc+0x98/0xb0 mm/kasan/common.c:394
 kasan_kmalloc include/linux/kasan.h:260 [inline]
 __kmalloc_cache_noprof+0x243/0x390 mm/slub.c:4329
 kmalloc_noprof include/linux/slab.h:901 [inline]
 kzalloc_noprof include/linux/slab.h:1037 [inline]
 l2cap_conn_add+0xa9/0x8e0 net/bluetooth/l2cap_core.c:6860
 l2cap_connect_cfm+0x115/0x1090 net/bluetooth/l2cap_core.c:7239
 hci_connect_cfm include/net/bluetooth/hci_core.h:2057 [inline]
 hci_remote_features_evt+0x68e/0xac0 net/bluetooth/hci_event.c:3726
 hci_event_func net/bluetooth/hci_event.c:7473 [inline]
 hci_event_packet+0xac2/0x1540 net/bluetooth/hci_event.c:7525
 hci_rx_work+0x3f3/0xdb0 net/bluetooth/hci_core.c:4035
 process_one_work kernel/workqueue.c:3229 [inline]
 process_scheduled_works+0xa66/0x1840 kernel/workqueue.c:3310
 worker_thread+0x870/0xd30 kernel/workqueue.c:3391
 kthread+0x2f0/0x390 kernel/kthread.c:389
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

Freed by task 54:
 kasan_save_stack mm/kasan/common.c:47 [inline]
 kasan_save_track+0x3f/0x80 mm/kasan/common.c:68
 kasan_save_free_info+0x40/0x50 mm/kasan/generic.c:582
 poison_slab_object mm/kasan/common.c:247 [inline]
 __kasan_slab_free+0x59/0x70 mm/kasan/common.c:264
 kasan_slab_free include/linux/kasan.h:233 [inline]
 slab_free_hook mm/slub.c:2353 [inline]
 slab_free mm/slub.c:4613 [inline]
 kfree+0x196/0x430 mm/slub.c:4761
 l2cap_connect_cfm+0xcc/0x1090 net/bluetooth/l2cap_core.c:7235
 hci_connect_cfm include/net/bluetooth/hci_core.h:2057 [inline]
 hci_conn_failed+0x287/0x400 net/bluetooth/hci_conn.c:1266
 hci_abort_conn_sync+0x56c/0x11f0 net/bluetooth/hci_sync.c:5603
 hci_cmd_sync_work+0x22b/0x400 net/bluetooth/hci_sync.c:332
 process_one_work kernel/workqueue.c:3229 [inline]
 process_scheduled_works+0xa66/0x1840 kernel/workqueue.c:3310
 worker_thread+0x870/0xd30 kernel/workqueue.c:3391
 kthread+0x2f0/0x390 kernel/kthread.c:389
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

Reported-by: syzbot+31c2f641b850a348a734@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=31c2f641b850a348a734
Tested-by: syzbot+31c2f641b850a348a734@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
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@Vudentz
Vudentz committed Feb 13, 2025
1 parent 0469b41 commit b4f82f9
Showing 1 changed file with 34 additions and 5 deletions.
39 changes: 34 additions & 5 deletions net/bluetooth/l2cap_core.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -948,6 +948,16 @@ static u8 l2cap_get_ident(struct l2cap_conn *conn)
return id;
}

static void l2cap_send_acl(struct l2cap_conn *conn, struct sk_buff *skb,
u8 flags)
{
/* Check if the hcon still valid before attempting to send */
if (hci_conn_valid(conn->hcon->hdev, conn->hcon))
hci_send_acl(conn->hchan, skb, flags);
else
kfree_skb(skb);
}

static void l2cap_send_cmd(struct l2cap_conn *conn, u8 ident, u8 code, u16 len,
void *data)
{
Expand All @@ -970,7 +980,7 @@ static void l2cap_send_cmd(struct l2cap_conn *conn, u8 ident, u8 code, u16 len,
bt_cb(skb)->force_active = BT_POWER_FORCE_ACTIVE_ON;
skb->priority = HCI_PRIO_MAX;

hci_send_acl(conn->hchan, skb, flags);
l2cap_send_acl(conn, skb, flags);
}

static void l2cap_do_send(struct l2cap_chan *chan, struct sk_buff *skb)
Expand Down Expand Up @@ -1792,20 +1802,18 @@ static void l2cap_conn_del(struct hci_conn *hcon, int err)

mutex_unlock(&conn->chan_lock);

hci_chan_del(conn->hchan);

if (conn->info_state & L2CAP_INFO_FEAT_MASK_REQ_SENT)
cancel_delayed_work_sync(&conn->info_timer);

hcon->l2cap_data = NULL;
conn->hchan = NULL;
l2cap_conn_put(conn);
}

static void l2cap_conn_free(struct kref *ref)
{
struct l2cap_conn *conn = container_of(ref, struct l2cap_conn, ref);

hci_chan_del(conn->hchan);
hci_conn_put(conn->hcon);
kfree(conn);
}
Expand Down Expand Up @@ -7466,14 +7474,33 @@ static void l2cap_recv_reset(struct l2cap_conn *conn)
conn->rx_len = 0;
}

static struct l2cap_conn *l2cap_conn_hold_unless_zero(struct l2cap_conn *c)
{
BT_DBG("conn %p orig refcnt %u", c, kref_read(&c->ref));

if (!kref_get_unless_zero(&c->ref))
return NULL;

return c;
}

void l2cap_recv_acldata(struct hci_conn *hcon, struct sk_buff *skb, u16 flags)
{
struct l2cap_conn *conn = hcon->l2cap_data;
struct l2cap_conn *conn;
int len;

/* Lock hdev to access l2cap_data to avoid race with l2cap_conn_del */
hci_dev_lock(hcon->hdev);

conn = hcon->l2cap_data;

if (!conn)
conn = l2cap_conn_add(hcon);

conn = l2cap_conn_hold_unless_zero(conn);

hci_dev_unlock(hcon->hdev);

if (!conn)
goto drop;

Expand Down Expand Up @@ -7565,6 +7592,8 @@ void l2cap_recv_acldata(struct hci_conn *hcon, struct sk_buff *skb, u16 flags)
break;
}

l2cap_conn_put(conn);

drop:
kfree_skb(skb);
}
Expand Down

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