Re: [RESEND 1/1] Bluetooth: Use chan_list_lock to protect the whole put/destroy invokation

From: Lee Jones
Date: Wed Jul 06 2022 - 06:53:49 EST

On Tue, 05 Jul 2022, Luiz Augusto von Dentz wrote:

> Hi Lee,
>
> On Wed, Jun 29, 2022 at 8:28 AM Lee Jones <lee.jones@xxxxxxxxxx> wrote:
> >
> > On Tue, 28 Jun 2022, Luiz Augusto von Dentz wrote:
> >
> > > Hi Eric, Lee,
> > >
> > > On Mon, Jun 27, 2022 at 4:39 PM Luiz Augusto von Dentz
> > > <luiz.dentz@xxxxxxxxx> wrote:
> > > >
> > > > Hi Eric, Lee,
> > > >
> > > > On Mon, Jun 27, 2022 at 7:41 AM Eric Dumazet <edumazet@xxxxxxxxxx> wrote:
> > > > >
> > > > > On Wed, Jun 22, 2022 at 10:27 AM Lee Jones <lee.jones@xxxxxxxxxx> wrote:
> > > > > >
> > > > > > This change prevents a use-after-free caused by one of the worker
> > > > > > threads starting up (see below) *after* the final channel reference
> > > > > > has been put() during sock_close() but *before* the references to the
> > > > > > channel have been destroyed.
> > > > > >
> > > > > > refcount_t: increment on 0; use-after-free.
> > > > > > BUG: KASAN: use-after-free in refcount_dec_and_test+0x20/0xd0
> > > > > > Read of size 4 at addr ffffffc114f5bf18 by task kworker/u17:14/705
> > > > > >
> > > > > > CPU: 4 PID: 705 Comm: kworker/u17:14 Tainted: G S W 4.14.234-00003-g1fb6d0bd49a4-dirty #28
> > > > > > Hardware name: Qualcomm Technologies, Inc. SM8150 V2 PM8150 Google Inc. MSM sm8150 Flame DVT (DT)
> > > > > > Workqueue: hci0 hci_rx_work
> > > > > > Call trace:
> > > > > > dump_backtrace+0x0/0x378
> > > > > > show_stack+0x20/0x2c
> > > > > > dump_stack+0x124/0x148
> > > > > > print_address_description+0x80/0x2e8
> > > > > > __kasan_report+0x168/0x188
> > > > > > kasan_report+0x10/0x18
> > > > > > __asan_load4+0x84/0x8c
> > > > > > refcount_dec_and_test+0x20/0xd0
> > > > > > l2cap_chan_put+0x48/0x12c
> > > > > > l2cap_recv_frame+0x4770/0x6550
> > > > > > l2cap_recv_acldata+0x44c/0x7a4
> > > > > > hci_acldata_packet+0x100/0x188
> > > > > > hci_rx_work+0x178/0x23c
> > > > > > process_one_work+0x35c/0x95c
> > > > > > worker_thread+0x4cc/0x960
> > > > > > kthread+0x1a8/0x1c4
> > > > > > ret_from_fork+0x10/0x18
> > > > > >
> > > > > > Cc: stable@xxxxxxxxxx
> > > > >
> > > > > When was the bug added ? (Fixes: tag please)
> > > > >
> > > > > > Cc: Marcel Holtmann <marcel@xxxxxxxxxxxx>
> > > > > > Cc: Johan Hedberg <johan.hedberg@xxxxxxxxx>
> > > > > > Cc: Luiz Augusto von Dentz <luiz.dentz@xxxxxxxxx>
> > > > > > Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> > > > > > Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
> > > > > > Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
> > > > > > Cc: Paolo Abeni <pabeni@xxxxxxxxxx>
> > > > > > Cc: linux-bluetooth@xxxxxxxxxxxxxxx
> > > > > > Cc: netdev@xxxxxxxxxxxxxxx
> > > > > > Signed-off-by: Lee Jones <lee.jones@xxxxxxxxxx>
> > > > > > ---
> > > > > > net/bluetooth/l2cap_core.c | 4 ++--
> > > > > > 1 file changed, 2 insertions(+), 2 deletions(-)
> > > > > >
> > > > > > diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> > > > > > index ae78490ecd3d4..82279c5919fd8 100644
> > > > > > --- a/net/bluetooth/l2cap_core.c
> > > > > > +++ b/net/bluetooth/l2cap_core.c
> > > > > > @@ -483,9 +483,7 @@ static void l2cap_chan_destroy(struct kref *kref)
> > > > > >
> > > > > > BT_DBG("chan %p", chan);
> > > > > >
> > > > > > - write_lock(&chan_list_lock);
> > > > > > list_del(&chan->global_l);
> > > > > > - write_unlock(&chan_list_lock);
> > > > > >
> > > > > > kfree(chan);
> > > > > > }
> > > > > > @@ -501,7 +499,9 @@ void l2cap_chan_put(struct l2cap_chan *c)
> > > > > > {
> > > > > > BT_DBG("chan %p orig refcnt %u", c, kref_read(&c->kref));
> > > > > >
> > > > > > + write_lock(&chan_list_lock);
> > > > > > kref_put(&c->kref, l2cap_chan_destroy);
> > > > > > + write_unlock(&chan_list_lock);
> > > > > > }
> > > > > > EXPORT_SYMBOL_GPL(l2cap_chan_put);
> > > > > >
> > > > > >
> > > > >
> > > > > I do not think this patch is correct.
> > > > >
> > > > > a kref does not need to be protected by a write lock.
> > > > >
> > > > > This might shuffle things enough to work around a particular repro you have.
> > > > >
> > > > > If the patch was correct why not protect kref_get() sides ?
> > > > >
> > > > > Before the &hdev->rx_work is scheduled (queue_work(hdev->workqueue,
> > > > > &hdev->rx_work),
> > > > > a reference must be taken.
> > > > >
> > > > > Then this reference must be released at the end of hci_rx_work() or
> > > > > when hdev->workqueue
> > > > > is canceled.
> > > > >
> > > > > This refcount is not needed _if_ the workqueue is properly canceled at
> > > > > device dismantle,
> > > > > in a synchronous way.
> > > > >
> > > > > I do not see this hdev->rx_work being canceled, maybe this is the real issue.
> > > > >
> > > > > There is a call to drain_workqueue() but this is not enough I think,
> > > > > because hci_recv_frame()
> > > > > can re-arm
> > > > > queue_work(hdev->workqueue, &hdev->rx_work);
> > > >
> > > > I suspect this likely a refcount problem, we do l2cap_get_chan_by_scid:
> > > >
> > > > /* Find channel with given SCID.
> > > > * Returns locked channel. */
> > > > static struct l2cap_chan *l2cap_get_chan_by_scid(struct l2cap_conn
> > > > *conn, u16 cid)
> > > >
> > > > So we return a locked channel but that doesn't prevent another thread
> > > > to call l2cap_chan_put which doesn't care about l2cap_chan_lock so
> > > > perhaps we actually need to host a reference while we have the lock,
> > > > at least we do something like that on l2cap_sock.c:
> > > >
> > > > l2cap_chan_hold(chan);
> > > > l2cap_chan_lock(chan);
> > > >
> > > > __clear_chan_timer(chan);
> > > > l2cap_chan_close(chan, ECONNRESET);
> > > > l2cap_sock_kill(sk);
> > > >
> > > > l2cap_chan_unlock(chan);
> > > > l2cap_chan_put(chan);
> > >
> > > Perhaps something like this:
> >
> > I'm struggling to apply this for test:
> >
> > "error: corrupt patch at line 6"
>
> Check with the attached patch.

With the patch applied:

[ 188.825418][ T75] refcount_t: addition on 0; use-after-free.
[ 188.825418][ T75] refcount_t: addition on 0; use-after-free.
[ 188.840629][ T75] WARNING: CPU: 5 PID: 75 at lib/refcount.c:25 refcount_warn_saturate+0x147/0x1b0
[ 188.840629][ T75] WARNING: CPU: 5 PID: 75 at lib/refcount.c:25 refcount_warn_saturate+0x147/0x1b0
[ 188.862642][ T75] Modules linked in:
[ 188.862642][ T75] Modules linked in:
[ 188.871686][ T75] CPU: 5 PID: 75 Comm: kworker/u17:0 Not tainted 5.18.0-00005-gc3401a7ad65f #8
[ 188.871686][ T75] CPU: 5 PID: 75 Comm: kworker/u17:0 Not tainted 5.18.0-00005-gc3401a7ad65f #8
[ 188.892806][ T75] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.0-debian-1.16.0-4 04/01/2014
[ 188.892806][ T75] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.0-debian-1.16.0-4 04/01/2014
[ 188.917398][ T75] Workqueue: hci0 hci_rx_work
[ 188.917398][ T75] Workqueue: hci0 hci_rx_work
[ 188.928515][ T75] RIP: 0010:refcount_warn_saturate+0x147/0x1b0
[ 188.928515][ T75] RIP: 0010:refcount_warn_saturate+0x147/0x1b0
[ 188.943176][ T75] Code: c7 e0 a1 70 85 31 c0 e8 d7 c2 e8 fe 0f 0b eb a1 e8 fe 33 15 ff c6 05 f9 e2 a5 04 01 48 c7 c7 80 a2 70 80
[ 188.943176][ T75] Code: c7 e0 a1 70 85 31 c0 e8 d7 c2 e8 fe 0f 0b eb a1 e8 fe 33 15 ff c6 05 f9 e2 a5 04 01 48 c7 c7 80 a2 70 80
[ 188.990053][ T75] RSP: 0018:ffffc9000156f800 EFLAGS: 00010246
[ 188.990053][ T75] RSP: 0018:ffffc9000156f800 EFLAGS: 00010246
[ 189.004337][ T75] RAX: 118d918bf1a47e00 RBX: 0000000000000002 RCX: ffff8881130ce000
[ 189.004337][ T75] RAX: 118d918bf1a47e00 RBX: 0000000000000002 RCX: ffff8881130ce000
[ 189.023131][ T75] RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
[ 189.023131][ T75] RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
[ 189.042044][ T75] RBP: ffffc9000156f810 R08: ffffffff81574218 R09: ffffed107de165d1
[ 189.042044][ T75] RBP: ffffc9000156f810 R08: ffffffff81574218 R09: ffffed107de165d1
[ 189.060967][ T75] R10: ffffed107de165d1 R11: 0000000000000000 R12: 1ffff920002adf10
[ 189.060967][ T75] R10: ffffed107de165d1 R11: 0000000000000000 R12: 1ffff920002adf10
[ 189.079650][ T75] R13: dffffc0000000000 R14: 0000000000000002 R15: ffff888139224818
[ 189.079650][ T75] R13: dffffc0000000000 R14: 0000000000000002 R15: ffff888139224818
[ 189.098573][ T75] FS: 0000000000000000(0000) GS:ffff8883ef080000(0000) knlGS:0000000000000000
[ 189.098573][ T75] FS: 0000000000000000(0000) GS:ffff8883ef080000(0000) knlGS:0000000000000000
[ 189.119604][ T75] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 189.119604][ T75] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 189.135313][ T75] CR2: 00000000004a2e98 CR3: 000000000680f000 CR4: 0000000000350ea0
[ 189.135313][ T75] CR2: 00000000004a2e98 CR3: 000000000680f000 CR4: 0000000000350ea0
[ 189.154165][ T75] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 189.154165][ T75] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 189.173465][ T75] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 189.173465][ T75] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 189.192075][ T75] Call Trace:
[ 189.192075][ T75] Call Trace:
[ 189.199853][ T75] <TASK>
[ 189.199853][ T75] <TASK>
[ 189.206820][ T75] l2cap_global_chan_by_psm+0x55a/0x5a0
[ 189.206820][ T75] l2cap_global_chan_by_psm+0x55a/0x5a0
[ 189.219891][ T75] ? l2cap_connect+0x12c0/0x12c0
[ 189.219891][ T75] ? l2cap_connect+0x12c0/0x12c0
[ 189.231602][ T75] ? __kfree_skb+0x13e/0x1c0
[ 189.231602][ T75] ? __kfree_skb+0x13e/0x1c0
[ 189.242612][ T75] ? l2cap_recv_frame+0xf5c/0x95c0
[ 189.242612][ T75] ? l2cap_recv_frame+0xf5c/0x95c0
[ 189.254714][ T75] ? skb_pull+0xde/0x150
[ 189.254714][ T75] ? skb_pull+0xde/0x150
[ 189.264776][ T75] l2cap_recv_frame+0x5bd/0x95c0
[ 189.264776][ T75] l2cap_recv_frame+0x5bd/0x95c0
[ 189.276329][ T75] ? debug_smp_processor_id+0x1c/0x20
[ 189.276329][ T75] ? debug_smp_processor_id+0x1c/0x20
[ 189.288985][ T75] ? update_cfs_rq_load_avg+0x412/0x4f0
[ 189.288985][ T75] ? update_cfs_rq_load_avg+0x412/0x4f0
[ 189.302202][ T75] ? l2cap_recv_acldata+0x1a60/0x1a60
[ 189.302202][ T75] ? l2cap_recv_acldata+0x1a60/0x1a60
[ 189.314998][ T75] ? __kasan_check_write+0x14/0x20
[ 189.314998][ T75] ? __kasan_check_write+0x14/0x20
[ 189.326877][ T75] ? __switch_to+0x617/0x1060
[ 189.326877][ T75] ? __switch_to+0x617/0x1060
[ 189.337858][ T75] ? __kasan_check_write+0x14/0x20
[ 189.337858][ T75] ? __kasan_check_write+0x14/0x20
[ 189.349712][ T75] ? _raw_spin_lock_irqsave+0xdc/0x1f0
[ 189.349712][ T75] ? _raw_spin_lock_irqsave+0xdc/0x1f0
[ 189.362793][ T75] ? compat_start_thread+0x20/0x20
[ 189.362793][ T75] ? compat_start_thread+0x20/0x20
[ 189.375316][ T75] l2cap_recv_acldata+0x5c9/0x1a60
[ 189.375316][ T75] l2cap_recv_acldata+0x5c9/0x1a60
[ 189.387262][ T75] ? hci_connect_sco+0x9b0/0x9b0
[ 189.387262][ T75] ? hci_connect_sco+0x9b0/0x9b0
[ 189.398857][ T75] hci_rx_work+0x54b/0x750
[ 189.398857][ T75] hci_rx_work+0x54b/0x750
[ 189.409172][ T75] process_one_work+0x6eb/0x1080
[ 189.409172][ T75] process_one_work+0x6eb/0x1080
[ 189.420829][ T75] worker_thread+0xb2b/0x13d0
[ 189.420829][ T75] worker_thread+0xb2b/0x13d0
[ 189.431922][ T75] kthread+0x2b1/0x2d0
[ 189.431922][ T75] kthread+0x2b1/0x2d0
[ 189.441724][ T75] ? process_one_work+0x1080/0x1080
[ 189.441724][ T75] ? process_one_work+0x1080/0x1080
[ 189.454559][ T75] ? kthread_blkcg+0xd0/0xd0
[ 189.454559][ T75] ? kthread_blkcg+0xd0/0xd0
[ 189.465457][ T75] ret_from_fork+0x1f/0x30
[ 189.465457][ T75] ret_from_fork+0x1f/0x30
[ 189.475777][ T75] </TASK>
[ 189.475777][ T75] </TASK>
[ 189.482907][ T75] ---[ end trace 0000000000000000 ]---
[ 189.482907][ T75] ---[ end trace 0000000000000000 ]---
[ 189.496567][ T75] ------------[ cut here ]------------
[ 189.496567][ T75] ------------[ cut here ]------------
[ 189.510250][ T75] refcount_t: underflow; use-after-free.
[ 189.510250][ T75] refcount_t: underflow; use-after-free.

> From 88cf6b4f2b0c9ed0bd7ef3b0d38574b412264609 Mon Sep 17 00:00:00 2001
> From: Luiz Augusto von Dentz <luiz.von.dentz@xxxxxxxxx>
> Date: Tue, 28 Jun 2022 15:46:04 -0700
> Subject: [PATCH] Bluetooth: L2CAP: WIP
>
> Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@xxxxxxxxx>
> ---
> net/bluetooth/l2cap_core.c | 25 +++++++++++++++++++------
> 1 file changed, 19 insertions(+), 6 deletions(-)
>
> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> index 09ecaf556de5..359fb1ce4372 100644
> --- a/net/bluetooth/l2cap_core.c
> +++ b/net/bluetooth/l2cap_core.c
> @@ -111,7 +111,8 @@ static struct l2cap_chan *__l2cap_get_chan_by_scid(struct l2cap_conn *conn,
> }
>
> /* Find channel with given SCID.
> - * Returns locked channel. */
> + * Returns a reference locked channel.
> + */
> static struct l2cap_chan *l2cap_get_chan_by_scid(struct l2cap_conn *conn,
> u16 cid)
> {
> @@ -119,15 +120,17 @@ static struct l2cap_chan *l2cap_get_chan_by_scid(struct l2cap_conn *conn,
>
> mutex_lock(&conn->chan_lock);
> c = __l2cap_get_chan_by_scid(conn, cid);
> - if (c)
> + if (c) {
> + l2cap_chan_hold(c);
> l2cap_chan_lock(c);
> + }
> mutex_unlock(&conn->chan_lock);
>
> return c;
> }
>
> /* Find channel with given DCID.
> - * Returns locked channel.
> + * Returns a reference locked channel.
> */
> static struct l2cap_chan *l2cap_get_chan_by_dcid(struct l2cap_conn *conn,
> u16 cid)
> @@ -136,8 +139,10 @@ static struct l2cap_chan *l2cap_get_chan_by_dcid(struct l2cap_conn *conn,
>
> mutex_lock(&conn->chan_lock);
> c = __l2cap_get_chan_by_dcid(conn, cid);
> - if (c)
> + if (c) {
> + l2cap_chan_hold(c);
> l2cap_chan_lock(c);
> + }
> mutex_unlock(&conn->chan_lock);
>
> return c;
> @@ -4464,6 +4469,7 @@ static inline int l2cap_config_req(struct l2cap_conn *conn,
>
> unlock:
> l2cap_chan_unlock(chan);
> + l2cap_chan_put(chan);
> return err;
> }
>
> @@ -4578,6 +4584,7 @@ static inline int l2cap_config_rsp(struct l2cap_conn *conn,
>
> done:
> l2cap_chan_unlock(chan);
> + l2cap_chan_put(chan);
> return err;
> }
>
> @@ -5305,6 +5312,7 @@ static inline int l2cap_move_channel_req(struct l2cap_conn *conn,
> l2cap_send_move_chan_rsp(chan, result);
>
> l2cap_chan_unlock(chan);
> + l2cap_chan_put(chan);
>
> return 0;
> }
> @@ -5397,6 +5405,7 @@ static void l2cap_move_continue(struct l2cap_conn *conn, u16 icid, u16 result)
> }
>
> l2cap_chan_unlock(chan);
> + l2cap_chan_put(chan);
> }
>
> static void l2cap_move_fail(struct l2cap_conn *conn, u8 ident, u16 icid,
> @@ -5489,6 +5498,7 @@ static int l2cap_move_channel_confirm(struct l2cap_conn *conn,
> l2cap_send_move_chan_cfm_rsp(conn, cmd->ident, icid);
>
> l2cap_chan_unlock(chan);
> + l2cap_chan_put(chan);
>
> return 0;
> }
> @@ -5524,6 +5534,7 @@ static inline int l2cap_move_channel_confirm_rsp(struct l2cap_conn *conn,
> }
>
> l2cap_chan_unlock(chan);
> + l2cap_chan_put(chan);
>
> return 0;
> }
> @@ -5896,12 +5907,11 @@ static inline int l2cap_le_credits(struct l2cap_conn *conn,
> if (credits > max_credits) {
> BT_ERR("LE credits overflow");
> l2cap_send_disconn_req(chan, ECONNRESET);
> - l2cap_chan_unlock(chan);
>
> /* Return 0 so that we don't trigger an unnecessary
> * command reject packet.
> */
> - return 0;
> + goto unlock;
> }
>
> chan->tx_credits += credits;
> @@ -5912,7 +5922,9 @@ static inline int l2cap_le_credits(struct l2cap_conn *conn,
> if (chan->tx_credits)
> chan->ops->resume(chan);
>
> +unlock:
> l2cap_chan_unlock(chan);
> + l2cap_chan_put(chan);
>
> return 0;
> }
> @@ -7598,6 +7610,7 @@ static void l2cap_data_channel(struct l2cap_conn *conn, u16 cid,
>
> done:
> l2cap_chan_unlock(chan);
> + l2cap_chan_put(chan);
> }
>
> static void l2cap_conless_channel(struct l2cap_conn *conn, __le16 psm,


--
Lee Jones [李琼斯]
Principal Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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