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Message-ID: <tencent_EA71777E46CCD36D236B696043AA444DD705@qq.com>
Date: Sat, 21 Sep 2024 09:40:52 +0800
From: Edward Adam Davis <eadavis@...com>
To: luiz.dentz@...il.com
Cc: eadavis@...com,
johan.hedberg@...il.com,
linux-bluetooth@...r.kernel.org,
linux-kernel@...r.kernel.org,
marcel@...tmann.org,
syzbot+c12e2f941af1feb5632c@...kaller.appspotmail.com,
syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH] Bluetooth/l2cap: Fix uaf in l2cap_connect
On Fri, 20 Sep 2024 11:07:05 -0400, Luiz Augusto von Dentz wrote:
> On Tue, Sep 10, 2024 at 4:56 PM Luiz Augusto von Dentz
> <luiz.dentz@...il.com> wrote:
> >
> > Hi Edward,
> >
> > On Sun, Sep 8, 2024 at 3:22 AM Edward Adam Davis <eadavis@...com> 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@...kaller.appspotmail.com
> > > Closes: https://syzkaller.appspot.com/bug?extid=c12e2f941af1feb5632c
> > > Signed-off-by: Edward Adam Davis <eadavis@...com>
> > > ---
> > > 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.
I haven't thought of any better way yet. I understand what you mean, holding
hci_dev_lock for a long time.
At present, it is not impossible to try some strong drugs.
> >
> > >
> > > 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@...el.com>
> > 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@...el.com>
> > Tested-by: Tedd Ho-Jeong An <tedd.an@...el.com>
> >
> > 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.
I think 7B064edae38d is used to solve another issue.
> >
> > Maybe something like the following would be a better approach:
> >
> > https://gist.github.com/Vudentz/121a15fa4391b2b1f6c7e8d420a6846e
>
> Any comments? Are you still planning to work on this?
Sorry for late.
>
> > >
> > > l2cap_connect(conn, cmd, data, L2CAP_CONN_RSP);
> > > return 0;
> > > --
> > > 2.43.0
> > >
> >
> >
> > --
> > Luiz Augusto von Dentz
BR,
Edward
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