[PATCH AUTOSEL 6.6 17/17] Bluetooth: L2CAP: Fix slab-use-after-free Read in l2cap_send_cmd

Sasha Levin
2025-02-18T20:28:17Z

From: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

[ Upstream commit b4f82f9ed43aefa79bec2504ae8c29be0c0f5d1d ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/bluetooth/l2cap_core.c | 39 +++++++++++++++++++++++++++++++++-----
1 file changed, 34 insertions(+), 5 deletions(-)

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index acb148759bd04..8680c8fc168ec 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -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)
{
@@ -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)
@@ -1792,13 +1802,10 @@ 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);
}

@@ -1806,6 +1813,7 @@ 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);
}
@@ -7472,14 +7480,33 @@ 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;

@@ -7571,6 +7598,8 @@ void l2cap_recv_acldata(struct hci_conn *hcon, struct sk_buff *skb, u16 flags)
break;
}

+ l2cap_conn_put(conn);
+
drop:
kfree_skb(skb);
}
--
2.39.5