Bluetooth: L2CAP: Fix slab-use-after-free Read in l2cap_send_cmd

JIRA: https://issues.redhat.com/browse/RHEL-87889
CVE: CVE-2025-21969

commit b4f82f9
Author: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Date:   Thu Jan 16 10:35:03 2025 -0500

    Bluetooth: L2CAP: Fix slab-use-after-free Read in l2cap_send_cmd

    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: CKI Backport Bot <cki-ci-bot+cki-gitlab-backport-bot@redhat.com>
Signed-off-by: David Marlin <dmarlin@redhat.com>

Author: CKI Backport Bot

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)
@@ -1792,20 +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);
 }
@@ -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;
 
@@ -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);
 }