Hi Edward, On Sun, Sep 8, 2024 at 3:22 AM Edward Adam Davis <eadavis@xxxxxx> wrote: > > [Syzbot reported] > BUG: KASAN: slab-use-after-free in l2cap_connect.constprop.0+0x10d8/0x1270 net/bluetooth/l2cap_core.c:3949 > Read of size 8 at addr ffff8880241e9800 by task kworker/u9:0/54 > > CPU: 0 UID: 0 PID: 54 Comm: kworker/u9:0 Not tainted 6.11.0-rc6-syzkaller-00268-g788220eee30d #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/06/2024 > Workqueue: hci2 hci_rx_work > Call Trace: > <TASK> > __dump_stack lib/dump_stack.c:93 [inline] > dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:119 > print_address_description mm/kasan/report.c:377 [inline] > print_report+0xc3/0x620 mm/kasan/report.c:488 > kasan_report+0xd9/0x110 mm/kasan/report.c:601 > l2cap_connect.constprop.0+0x10d8/0x1270 net/bluetooth/l2cap_core.c:3949 > l2cap_connect_req net/bluetooth/l2cap_core.c:4080 [inline] > l2cap_bredr_sig_cmd net/bluetooth/l2cap_core.c:4772 [inline] > l2cap_sig_channel net/bluetooth/l2cap_core.c:5543 [inline] > l2cap_recv_frame+0xf0b/0x8eb0 net/bluetooth/l2cap_core.c:6825 > l2cap_recv_acldata+0x9b4/0xb70 net/bluetooth/l2cap_core.c:7514 > hci_acldata_packet net/bluetooth/hci_core.c:3791 [inline] > hci_rx_work+0xaab/0x1610 net/bluetooth/hci_core.c:4028 > process_one_work+0x9c5/0x1b40 kernel/workqueue.c:3231 > process_scheduled_works kernel/workqueue.c:3312 [inline] > worker_thread+0x6c8/0xed0 kernel/workqueue.c:3389 > kthread+0x2c1/0x3a0 kernel/kthread.c:389 > ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147 > ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244 > ... > > Freed by task 5245: > kasan_save_stack+0x33/0x60 mm/kasan/common.c:47 > kasan_save_track+0x14/0x30 mm/kasan/common.c:68 > kasan_save_free_info+0x3b/0x60 mm/kasan/generic.c:579 > poison_slab_object+0xf7/0x160 mm/kasan/common.c:240 > __kasan_slab_free+0x32/0x50 mm/kasan/common.c:256 > kasan_slab_free include/linux/kasan.h:184 [inline] > slab_free_hook mm/slub.c:2256 [inline] > slab_free mm/slub.c:4477 [inline] > kfree+0x12a/0x3b0 mm/slub.c:4598 > l2cap_conn_free net/bluetooth/l2cap_core.c:1810 [inline] > kref_put include/linux/kref.h:65 [inline] > l2cap_conn_put net/bluetooth/l2cap_core.c:1822 [inline] > l2cap_conn_del+0x59d/0x730 net/bluetooth/l2cap_core.c:1802 > l2cap_connect_cfm+0x9e6/0xf80 net/bluetooth/l2cap_core.c:7241 > hci_connect_cfm include/net/bluetooth/hci_core.h:1960 [inline] > hci_conn_failed+0x1c3/0x370 net/bluetooth/hci_conn.c:1265 > hci_abort_conn_sync+0x75a/0xb50 net/bluetooth/hci_sync.c:5583 > abort_conn_sync+0x197/0x360 net/bluetooth/hci_conn.c:2917 > hci_cmd_sync_work+0x1a4/0x410 net/bluetooth/hci_sync.c:328 > process_one_work+0x9c5/0x1b40 kernel/workqueue.c:3231 > process_scheduled_works kernel/workqueue.c:3312 [inline] > worker_thread+0x6c8/0xed0 kernel/workqueue.c:3389 > kthread+0x2c1/0x3a0 kernel/kthread.c:389 > ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147 > ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244 > > [Analysis] > There was a data race when accessing conn in hci_rx_work and hci_cmd_sync_work. > This is because the hci dev lock was prematurely exited when executing > hci_acldata_macket() in hci_rx_work, which resulted in it being released > by hci_cmd_sync_work when accessing conn outside the lock. > > Reported-and-tested-by: syzbot+c12e2f941af1feb5632c@xxxxxxxxxxxxxxxxxxxxxxxxx > Closes: https://syzkaller.appspot.com/bug?extid=c12e2f941af1feb5632c > Signed-off-by: Edward Adam Davis <eadavis@xxxxxx> > --- > net/bluetooth/hci_core.c | 3 ++- > net/bluetooth/l2cap_core.c | 2 -- > 2 files changed, 2 insertions(+), 3 deletions(-) > > diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c > index f25a21f532aa..4f7b45bb863f 100644 > --- a/net/bluetooth/hci_core.c > +++ b/net/bluetooth/hci_core.c > @@ -3776,18 +3776,19 @@ static void hci_acldata_packet(struct hci_dev *hdev, struct sk_buff *skb) > > hci_dev_lock(hdev); > conn = hci_conn_hash_lookup_handle(hdev, handle); > - hci_dev_unlock(hdev); > > if (conn) { > hci_conn_enter_active_mode(conn, BT_POWER_FORCE_ACTIVE_OFF); > > /* Send to upper protocol */ > l2cap_recv_acldata(conn, skb, flags); > + hci_dev_unlock(hdev); > return; > } else { > bt_dev_err(hdev, "ACL packet for unknown connection handle %d", > handle); > } > + hci_dev_unlock(hdev); This is sort of risky, we shouldn't be calling this deep into the stack with hci_dev_lock held. > > kfree_skb(skb); > } > diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c > index 9988ba382b68..b948b0a3b2f2 100644 > --- a/net/bluetooth/l2cap_core.c > +++ b/net/bluetooth/l2cap_core.c > @@ -4072,10 +4072,8 @@ static int l2cap_connect_req(struct l2cap_conn *conn, > if (cmd_len < sizeof(struct l2cap_conn_req)) > return -EPROTO; > > - hci_dev_lock(hdev); > if (hci_dev_test_flag(hdev, HCI_MGMT)) > mgmt_device_connected(hdev, hcon, NULL, 0); > - hci_dev_unlock(hdev); So this might explain why things gets freed while processing the request, we are locking to call mgmt_device_connected which I suspect is no longer needed ever since: commit db11223571d489d1aab575a4ac4b7352d2d54e2f Author: Luiz Augusto von Dentz <luiz.von.dentz@xxxxxxxxx> Date: Tue Oct 25 14:12:58 2022 -0700 Bluetooth: btusb: Default CONFIG_BT_HCIBTUSB_POLL_SYNC=y poll_sync has been proven to fix races of USB data and event endpoints so this enables it by default. Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@xxxxxxxxx> Tested-by: Tedd Ho-Jeong An <tedd.an@xxxxxxxxx> Anyway syzbot don't use btusb so I think this might be due some command pending that the emulator is not responding and instead sending data, and then there is the issue that 7b064edae38d ("Bluetooth: Fix authentication if acl data comes before remote feature evt") attempted to fix which I think it actually made it worse by moving the call to mgmt_device_connected into l2cap_core.c it sort move the problem but didn't fix the actual problem. Maybe something like the following would be a better approach: https://gist.github.com/Vudentz/121a15fa4391b2b1f6c7e8d420a6846e > > l2cap_connect(conn, cmd, data, L2CAP_CONN_RSP); > return 0; > -- > 2.43.0 > -- Luiz Augusto von Dentz
