Hi Edward, On Wed, Jan 15, 2025 at 4:46 AM Edward Adam Davis <eadavis@xxxxxx> wrote: > > syzbot reported a slab-use-after-free Read in l2cap_send_cmd. [1] > > 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@xxxxxxxxxxxxxxxxxxxxxxxxx > Closes: https://syzkaller.appspot.com/bug?extid=31c2f641b850a348a734 > Tested-by: syzbot+31c2f641b850a348a734@xxxxxxxxxxxxxxxxxxxxxxxxx > Signed-off-by: Edward Adam Davis <eadavis@xxxxxx> > --- > net/bluetooth/hci_core.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c > index f9e19f9cb5a3..88c8aa37eb64 100644 > --- a/net/bluetooth/hci_core.c > +++ b/net/bluetooth/hci_core.c > @@ -3798,7 +3798,9 @@ static void hci_acldata_packet(struct hci_dev *hdev, struct sk_buff *skb) > hci_conn_enter_active_mode(conn, BT_POWER_FORCE_ACTIVE_OFF); > > /* Send to upper protocol */ > + hci_dev_lock(hdev); > l2cap_recv_acldata(conn, skb, flags); > + hci_dev_unlock(hdev); This will not gonna fly, there have been instances where l2cap code needs to lock hdev so this most likely causes a deadlock, besides we used to have such design of locking hdev for everything but that doesn't scale very well. Instead, perhaps we can do something like the following: diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c index 27b4c4a2ba1f..023e3ebe0e39 100644 --- a/net/bluetooth/l2cap_core.c +++ b/net/bluetooth/l2cap_core.c @@ -7466,6 +7466,16 @@ 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; @@ -7474,6 +7484,7 @@ void l2cap_recv_acldata(struct hci_conn *hcon, struct sk_buff *skb, u16 flags) if (!conn) conn = l2cap_conn_add(hcon); + conn = l2cap_conn_hold_unless_zero(conn); if (!conn) goto drop; @@ -7565,6 +7576,8 @@ void l2cap_recv_acldata(struct hci_conn *hcon, struct sk_buff *skb, u16 flags) break; } + l2cap_conn_put(conn); + drop: kfree_skb(skb); } > return; > } else { > bt_dev_err(hdev, "ACL packet for unknown connection handle %d", > -- > 2.47.0 > -- Luiz Augusto von Dentz
