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Message-ID: <YrxvgIiWuFVlXBaQ@google.com>
Date: Wed, 29 Jun 2022 16:28:00 +0100
From: Lee Jones <lee.jones@...aro.org>
To: Luiz Augusto von Dentz <luiz.dentz@...il.com>
Cc: Eric Dumazet <edumazet@...gle.com>,
LKML <linux-kernel@...r.kernel.org>, stable@...nel.org,
Marcel Holtmann <marcel@...tmann.org>,
Johan Hedberg <johan.hedberg@...il.com>,
"David S. Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
"linux-bluetooth@...r.kernel.org" <linux-bluetooth@...r.kernel.org>,
netdev <netdev@...r.kernel.org>
Subject: Re: [RESEND 1/1] Bluetooth: Use chan_list_lock to protect the whole
put/destroy invokation
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@...il.com> wrote:
> >
> > Hi Eric, Lee,
> >
> > On Mon, Jun 27, 2022 at 7:41 AM Eric Dumazet <edumazet@...gle.com> wrote:
> > >
> > > On Wed, Jun 22, 2022 at 10:27 AM Lee Jones <lee.jones@...aro.org> 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@...nel.org
> > >
> > > When was the bug added ? (Fixes: tag please)
> > >
> > > > Cc: Marcel Holtmann <marcel@...tmann.org>
> > > > Cc: Johan Hedberg <johan.hedberg@...il.com>
> > > > Cc: Luiz Augusto von Dentz <luiz.dentz@...il.com>
> > > > Cc: "David S. Miller" <davem@...emloft.net>
> > > > Cc: Eric Dumazet <edumazet@...gle.com>
> > > > Cc: Jakub Kicinski <kuba@...nel.org>
> > > > Cc: Paolo Abeni <pabeni@...hat.com>
> > > > Cc: linux-bluetooth@...r.kernel.org
> > > > Cc: netdev@...r.kernel.org
> > > > Signed-off-by: Lee Jones <lee.jones@...aro.org>
> > > > ---
> > > > 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"
Please could you attach a `git format-patch`ed patch instead?
> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> index 09ecaf556de5..9050b6af3577 100644
> --- a/net/bluetooth/l2cap_core.c
> +++ b/net/bluetooth/l2cap_core.c
> @@ -111,7 +111,7 @@ 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 +119,17 @@ 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 +138,10 @@ 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 +4468,7 @@ static inline int l2cap_config_req(struct
> l2cap_conn *conn,
>
> unlock:
> l2cap_chan_unlock(chan);
> + l2cap_chan_put(chan);
> return err;
> }
>
> @@ -4578,6 +4583,7 @@ static inline int l2cap_config_rsp(struct
> l2cap_conn *conn,
>
> done:
> l2cap_chan_unlock(chan);
> + l2cap_chan_put(chan);
> return err;
> }
>
> @@ -5305,6 +5311,7 @@ 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 +5404,7 @@ 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 +5497,7 @@ 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 +5533,7 @@ static inline int
> l2cap_move_channel_confirm_rsp(struct l2cap_conn *conn,
> }
>
> l2cap_chan_unlock(chan);
> + l2cap_chan_put(chan);
>
> return 0;
> }
> @@ -5896,12 +5906,11 @@ 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 +5921,9 @@ 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 +7609,7 @@ 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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