Hi Maxim, On Mon, Oct 3, 2022 at 10:25 AM Maxim Mikityanskiy <maxtram95@xxxxxxxxx> 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@xxxxxxxxxxxxxx/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@xxxxxxxxx> > --- > 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
