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Date: Mon, 3 Oct 2022 12:13:10 -0700
From: Luiz Augusto von Dentz <luiz.dentz@...il.com>
To: Maxim Mikityanskiy <maxtram95@...il.com>
Cc: Marcel Holtmann <marcel@...tmann.org>,
Johan Hedberg <johan.hedberg@...il.com>,
Mat Martineau <mathew.j.martineau@...ux.intel.com>,
Gustavo Padovan <gustavo.padovan@...labora.co.uk>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
linux-bluetooth@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v2] Bluetooth: L2CAP: Fix use-after-free caused by l2cap_reassemble_sdu
Hi Maxim,
On Mon, Oct 3, 2022 at 10:25 AM Maxim Mikityanskiy <maxtram95@...il.com> wrote:
>
> Fix the race condition between the following two flows that run in
> parallel:
>
> 1. l2cap_reassemble_sdu -> chan->ops->recv -> l2cap_sock_recv_cb ->
> __sock_queue_rcv_skb.
>
> 2. bt_sock_recvmsg -> skb_recv_datagram, skb_free_datagram.
>
> An SKB can be queued by the first flow and immediately dequeued and
> freed by the second flow, therefore the callers of l2cap_reassemble_sdu
> can't use the SKB after that function returns. However, some places
> continue accessing struct l2cap_ctrl that resides in the SKB's CB for a
> short time after l2cap_reassemble_sdu returns, leading to a
> use-after-free condition (the stack trace is below, line numbers for
> kernel 5.19.8).
>
> Fix it by keeping a local copy of struct l2cap_ctrl.
>
> BUG: KASAN: use-after-free in l2cap_rx_state_recv (net/bluetooth/l2cap_core.c:6906) bluetooth
> Read of size 1 at addr ffff88812025f2f0 by task kworker/u17:3/43169
>
> Workqueue: hci0 hci_rx_work [bluetooth]
> Call Trace:
> <TASK>
> dump_stack_lvl (lib/dump_stack.c:107 (discriminator 4))
> print_report.cold (mm/kasan/report.c:314 mm/kasan/report.c:429)
> ? l2cap_rx_state_recv (net/bluetooth/l2cap_core.c:6906) bluetooth
> kasan_report (mm/kasan/report.c:162 mm/kasan/report.c:493)
> ? l2cap_rx_state_recv (net/bluetooth/l2cap_core.c:6906) bluetooth
> l2cap_rx_state_recv (net/bluetooth/l2cap_core.c:6906) bluetooth
> l2cap_rx (net/bluetooth/l2cap_core.c:7236 net/bluetooth/l2cap_core.c:7271) bluetooth
> ? sk_filter_trim_cap (net/core/filter.c:123)
> ? l2cap_chan_hold_unless_zero (./arch/x86/include/asm/atomic.h:202 ./include/linux/atomic/atomic-instrumented.h:560 ./include/linux/refcount.h:157 ./include/linux/refcount.h:227 ./include/linux/refcount.h:245 ./include/linux/kref.h:111 net/bluetooth/l2cap_core.c:517) bluetooth
> ? l2cap_rx_state_recv (net/bluetooth/l2cap_core.c:7252) bluetooth
> l2cap_recv_frame (net/bluetooth/l2cap_core.c:7405 net/bluetooth/l2cap_core.c:7620 net/bluetooth/l2cap_core.c:7723) bluetooth
> ? lock_release (./include/trace/events/lock.h:69 kernel/locking/lockdep.c:5677)
> ? hci_rx_work (net/bluetooth/hci_core.c:3637 net/bluetooth/hci_core.c:3832) bluetooth
> ? reacquire_held_locks (kernel/locking/lockdep.c:5674)
> ? trace_contention_end (./include/trace/events/lock.h:122 ./include/trace/events/lock.h:122)
> ? l2cap_config_rsp.isra.0 (net/bluetooth/l2cap_core.c:7674) bluetooth
> ? hci_rx_work (./include/net/bluetooth/hci_core.h:1024 net/bluetooth/hci_core.c:3634 net/bluetooth/hci_core.c:3832) bluetooth
> ? lock_acquire (./include/trace/events/lock.h:24 kernel/locking/lockdep.c:5637)
> ? __mutex_unlock_slowpath (./arch/x86/include/asm/atomic64_64.h:190 ./include/linux/atomic/atomic-long.h:449 ./include/linux/atomic/atomic-instrumented.h:1790 kernel/locking/mutex.c:924)
> ? rcu_read_lock_sched_held (kernel/rcu/update.c:104 kernel/rcu/update.c:123)
> ? memcpy (mm/kasan/shadow.c:65 (discriminator 1))
> ? l2cap_recv_frag (net/bluetooth/l2cap_core.c:8340) bluetooth
> l2cap_recv_acldata (net/bluetooth/l2cap_core.c:8486) bluetooth
> hci_rx_work (net/bluetooth/hci_core.c:3642 net/bluetooth/hci_core.c:3832) bluetooth
> process_one_work (kernel/workqueue.c:2289)
> ? lock_downgrade (kernel/locking/lockdep.c:5634)
> ? pwq_dec_nr_in_flight (kernel/workqueue.c:2184)
> ? rwlock_bug.part.0 (kernel/locking/spinlock_debug.c:113)
> worker_thread (./include/linux/list.h:292 kernel/workqueue.c:2437)
> ? __kthread_parkme (./arch/x86/include/asm/bitops.h:207 (discriminator 4) ./include/asm-generic/bitops/instrumented-non-atomic.h:135 (discriminator 4) kernel/kthread.c:270 (discriminator 4))
> ? process_one_work (kernel/workqueue.c:2379)
> kthread (kernel/kthread.c:376)
> ? kthread_complete_and_exit (kernel/kthread.c:331)
> ret_from_fork (arch/x86/entry/entry_64.S:306)
> </TASK>
>
> Allocated by task 43169:
> kasan_save_stack (mm/kasan/common.c:39)
> __kasan_slab_alloc (mm/kasan/common.c:45 mm/kasan/common.c:436 mm/kasan/common.c:469)
> kmem_cache_alloc_node (mm/slab.h:750 mm/slub.c:3243 mm/slub.c:3293)
> __alloc_skb (net/core/skbuff.c:414)
> l2cap_recv_frag (./include/net/bluetooth/bluetooth.h:425 net/bluetooth/l2cap_core.c:8329) bluetooth
> l2cap_recv_acldata (net/bluetooth/l2cap_core.c:8442) bluetooth
> hci_rx_work (net/bluetooth/hci_core.c:3642 net/bluetooth/hci_core.c:3832) bluetooth
> process_one_work (kernel/workqueue.c:2289)
> worker_thread (./include/linux/list.h:292 kernel/workqueue.c:2437)
> kthread (kernel/kthread.c:376)
> ret_from_fork (arch/x86/entry/entry_64.S:306)
>
> Freed by task 27920:
> kasan_save_stack (mm/kasan/common.c:39)
> kasan_set_track (mm/kasan/common.c:45)
> kasan_set_free_info (mm/kasan/generic.c:372)
> ____kasan_slab_free (mm/kasan/common.c:368 mm/kasan/common.c:328)
> slab_free_freelist_hook (mm/slub.c:1780)
> kmem_cache_free (mm/slub.c:3536 mm/slub.c:3553)
> skb_free_datagram (./include/net/sock.h:1578 ./include/net/sock.h:1639 net/core/datagram.c:323)
> bt_sock_recvmsg (net/bluetooth/af_bluetooth.c:295) bluetooth
> l2cap_sock_recvmsg (net/bluetooth/l2cap_sock.c:1212) bluetooth
> sock_read_iter (net/socket.c:1087)
> new_sync_read (./include/linux/fs.h:2052 fs/read_write.c:401)
> vfs_read (fs/read_write.c:482)
> ksys_read (fs/read_write.c:620)
> do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80)
> entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120)
>
> Link: https://lore.kernel.org/linux-bluetooth/CAKErNvoqga1WcmoR3-0875esY6TVWFQDandbVZncSiuGPBQXLA@mail.gmail.com/T/#u
> Fixes: d2a7ac5d5d3a ("Bluetooth: Add the ERTM receive state machine")
> Fixes: 4b51dae96731 ("Bluetooth: Add streaming mode receive and incoming packet classifier")
> Signed-off-by: Maxim Mikityanskiy <maxtram95@...il.com>
> ---
> net/bluetooth/l2cap_core.c | 17 ++++++++++-------
> 1 file changed, 10 insertions(+), 7 deletions(-)
>
> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> index 2c9de67daadc..6bdce147d2fe 100644
> --- a/net/bluetooth/l2cap_core.c
> +++ b/net/bluetooth/l2cap_core.c
> @@ -6876,6 +6876,7 @@ static int l2cap_rx_state_recv(struct l2cap_chan *chan,
> struct l2cap_ctrl *control,
> struct sk_buff *skb, u8 event)
> {
> + struct l2cap_ctrl local_control;
> int err = 0;
> bool skb_in_use = false;
>
> @@ -6900,15 +6901,16 @@ static int l2cap_rx_state_recv(struct l2cap_chan *chan,
> chan->buffer_seq = chan->expected_tx_seq;
> skb_in_use = true;
>
> + local_control = *control;
Have a comment on why we are creating a local copy, btw should we pass
the copy to l2cap_reassemble_sdu?
> err = l2cap_reassemble_sdu(chan, skb, control);
> if (err)
> break;
>
> - if (control->final) {
> + if (local_control.final) {
> if (!test_and_clear_bit(CONN_REJ_ACT,
> &chan->conn_state)) {
> - control->final = 0;
> - l2cap_retransmit_all(chan, control);
> + local_control.final = 0;
> + l2cap_retransmit_all(chan, &local_control);
> l2cap_ertm_send(chan);
> }
> }
> @@ -7288,11 +7290,12 @@ static int l2cap_rx(struct l2cap_chan *chan, struct l2cap_ctrl *control,
> static int l2cap_stream_rx(struct l2cap_chan *chan, struct l2cap_ctrl *control,
> struct sk_buff *skb)
> {
> + u16 txseq = control->txseq;
> +
> BT_DBG("chan %p, control %p, skb %p, state %d", chan, control, skb,
> chan->rx_state);
>
> - if (l2cap_classify_txseq(chan, control->txseq) ==
> - L2CAP_TXSEQ_EXPECTED) {
> + if (l2cap_classify_txseq(chan, txseq) == L2CAP_TXSEQ_EXPECTED) {
> l2cap_pass_to_tx(chan, control);
>
> BT_DBG("buffer_seq %u->%u", chan->buffer_seq,
> @@ -7315,8 +7318,8 @@ static int l2cap_stream_rx(struct l2cap_chan *chan, struct l2cap_ctrl *control,
> }
> }
>
> - chan->last_acked_seq = control->txseq;
> - chan->expected_tx_seq = __next_seq(chan, control->txseq);
> + chan->last_acked_seq = txseq;
> + chan->expected_tx_seq = __next_seq(chan, txseq);
>
> return 0;
> }
> --
> 2.37.3
>
--
Luiz Augusto von Dentz
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