On Wed, 15 Jan 2025 11:13:00 -0500 Luiz Augusto von Dentz <luiz.dentz@xxxxxxxxx> > 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); This does not work because conn can be freed before bumping refcnt up, and bumpup alone does not help l2cap_send_cmd() in case conn->hchan has been cleared in l2cap_conn_del(). > 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
