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Date:   Wed, 20 Jul 2022 10:10:07 -0700
From:   Luiz Augusto von Dentz <luiz.dentz@...il.com>
To:     Lee Jones <lee.jones@...aro.org>
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

Hi Lee,

On Wed, Jul 20, 2022 at 4:52 AM Lee Jones <lee.jones@...aro.org> wrote:
>
> On Wed, 06 Jul 2022, Luiz Augusto von Dentz wrote:
> > > > > > > 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.
> > >
> > > Looks like the changes just make the issue more visible since we are
> > > trying to add a refcount when it is already 0 so this proves the
> > > design is not quite right since it is removing the object from the
> > > list only when destroying it while we probably need to do it before.
> > >
> > > How about we use kref_get_unless_zero as it appears it was introduced
> > > exactly for such cases (patch attached.)
> >
> > Looks like I missed a few places like l2cap_global_chan_by_psm so here
> > is another version.
>
> Okay, with the patch below the kernel doesn't produce a back-trace.

Great, Ive send a patch with these changes.

> Only this, which I assume is expected?
>
> [  535.398255][  T495] Bluetooth: hci0: unexpected cc 0x0c03 length: 249 > 1
> [  535.398255][  T495] Bluetooth: hci0: unexpected cc 0x0c03 length: 249 > 1
> [  535.417007][  T495] Bluetooth: hci0: unexpected cc 0x1003 length: 249 > 9
> [  535.417007][  T495] Bluetooth: hci0: unexpected cc 0x1003 length: 249 > 9
> [  535.434810][  T495] Bluetooth: hci0: unexpected cc 0x1001 length: 249 > 9
> [  535.434810][  T495] Bluetooth: hci0: unexpected cc 0x1001 length: 249 > 9
> [  535.452886][  T495] Bluetooth: hci0: unexpected cc 0x0c23 length: 249 > 4
> [  535.452886][  T495] Bluetooth: hci0: unexpected cc 0x0c23 length: 249 > 4
> [  535.470574][  T495] Bluetooth: hci0: unexpected cc 0x0c25 length: 249 > 3
> [  535.470574][  T495] Bluetooth: hci0: unexpected cc 0x0c25 length: 249 > 3
> [  535.488009][  T495] Bluetooth: hci0: unexpected cc 0x0c38 length: 249 > 2
> [  535.488009][  T495] Bluetooth: hci0: unexpected cc 0x0c38 length: 249 > 2
> [  537.551677][   T74] Bluetooth: hci0: command 0x0409 tx timeout
> [  537.551677][   T74] Bluetooth: hci0: command 0x0409 tx timeout
> [  539.641362][  T373] Bluetooth: hci0: command 0x041b tx timeout
> [  539.641362][  T373] Bluetooth: hci0: command 0x041b tx timeout
> [  541.711056][  T274] Bluetooth: hci0: command 0x040f tx timeout
> [  541.711056][  T274] Bluetooth: hci0: command 0x040f tx timeout
> [  543.790939][   T66] Bluetooth: hci0: command 0x0419 tx timeout
> [  543.790939][   T66] Bluetooth: hci0: command 0x0419 tx timeout

Yep, if the test doesn't act according to the BT spec, those are expected.

> > From 235937ac7a39d16e5dabbfca0ac1d58e4cc814d9 Mon Sep 17 00:00:00 2001
> > From: Luiz Augusto von Dentz <luiz.von.dentz@...el.com>
> > Date: Tue, 28 Jun 2022 15:46:04 -0700
> > Subject: [PATCH] Bluetooth: L2CAP: WIP
> >
> > Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@...el.com>
> > ---
> >  include/net/bluetooth/l2cap.h |  1 +
> >  net/bluetooth/l2cap_core.c    | 58 +++++++++++++++++++++++++++--------
> >  2 files changed, 46 insertions(+), 13 deletions(-)
> >
> > diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h
> > index 3c4f550e5a8b..2f766e3437ce 100644
> > --- a/include/net/bluetooth/l2cap.h
> > +++ b/include/net/bluetooth/l2cap.h
> > @@ -847,6 +847,7 @@ enum {
> >  };
> >
> >  void l2cap_chan_hold(struct l2cap_chan *c);
> > +struct l2cap_chan *l2cap_chan_hold_unless_zero(struct l2cap_chan *c);
> >  void l2cap_chan_put(struct l2cap_chan *c);
> >
> >  static inline void l2cap_chan_lock(struct l2cap_chan *chan)
> > diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> > index 09ecaf556de5..3e5d81e971cc 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 +120,19 @@ 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)
> > -             l2cap_chan_lock(c);
> > +     if (c) {
> > +             /* Only lock if chan reference is not 0 */
> > +             c = l2cap_chan_hold_unless_zero(c);
> > +             if (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 +141,12 @@ 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)
> > -             l2cap_chan_lock(c);
> > +     if (c) {
> > +             /* Only lock if chan reference is not 0 */
> > +             c = l2cap_chan_hold_unless_zero(c);
> > +             if (c)
> > +                     l2cap_chan_lock(c);
> > +     }
> >       mutex_unlock(&conn->chan_lock);
> >
> >       return c;
> > @@ -162,8 +171,12 @@ static struct l2cap_chan *l2cap_get_chan_by_ident(struct l2cap_conn *conn,
> >
> >       mutex_lock(&conn->chan_lock);
> >       c = __l2cap_get_chan_by_ident(conn, ident);
> > -     if (c)
> > -             l2cap_chan_lock(c);
> > +     if (c) {
> > +             /* Only lock if chan reference is not 0 */
> > +             c = l2cap_chan_hold_unless_zero(c);
> > +             if (c)
> > +                     l2cap_chan_lock(c);
> > +     }
> >       mutex_unlock(&conn->chan_lock);
> >
> >       return c;
> > @@ -497,6 +510,16 @@ void l2cap_chan_hold(struct l2cap_chan *c)
> >       kref_get(&c->kref);
> >  }
> >
> > +struct l2cap_chan *l2cap_chan_hold_unless_zero(struct l2cap_chan *c)
> > +{
> > +     BT_DBG("chan %p orig refcnt %u", c, kref_read(&c->kref));
> > +
> > +     if (!kref_get_unless_zero(&c->kref))
> > +             return NULL;
> > +
> > +     return c;
> > +}
> > +
> >  void l2cap_chan_put(struct l2cap_chan *c)
> >  {
> >       BT_DBG("chan %p orig refcnt %u", c, kref_read(&c->kref));
> > @@ -1969,7 +1992,7 @@ static struct l2cap_chan *l2cap_global_chan_by_psm(int state, __le16 psm,
> >                       src_match = !bacmp(&c->src, src);
> >                       dst_match = !bacmp(&c->dst, dst);
> >                       if (src_match && dst_match) {
> > -                             l2cap_chan_hold(c);
> > +                             c = l2cap_chan_hold_unless_zero(c);
> >                               read_unlock(&chan_list_lock);
> >                               return c;
> >                       }
> > @@ -1984,7 +2007,7 @@ static struct l2cap_chan *l2cap_global_chan_by_psm(int state, __le16 psm,
> >       }
> >
> >       if (c1)
> > -             l2cap_chan_hold(c1);
> > +             c1 = l2cap_chan_hold_unless_zero(c1);
> >
> >       read_unlock(&chan_list_lock);
> >
> > @@ -4464,6 +4487,7 @@ static inline int l2cap_config_req(struct l2cap_conn *conn,
> >
> >  unlock:
> >       l2cap_chan_unlock(chan);
> > +     l2cap_chan_put(chan);
> >       return err;
> >  }
> >
> > @@ -4578,6 +4602,7 @@ static inline int l2cap_config_rsp(struct l2cap_conn *conn,
> >
> >  done:
> >       l2cap_chan_unlock(chan);
> > +     l2cap_chan_put(chan);
> >       return err;
> >  }
> >
> > @@ -5305,6 +5330,7 @@ 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 +5423,7 @@ 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,
> > @@ -5426,6 +5453,7 @@ static void l2cap_move_fail(struct l2cap_conn *conn, u8 ident, u16 icid,
> >       l2cap_send_move_chan_cfm(chan, L2CAP_MC_UNCONFIRMED);
> >
> >       l2cap_chan_unlock(chan);
> > +     l2cap_chan_put(chan);
> >  }
> >
> >  static int l2cap_move_channel_rsp(struct l2cap_conn *conn,
> > @@ -5489,6 +5517,7 @@ 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 +5553,7 @@ static inline int l2cap_move_channel_confirm_rsp(struct l2cap_conn *conn,
> >       }
> >
> >       l2cap_chan_unlock(chan);
> > +     l2cap_chan_put(chan);
> >
> >       return 0;
> >  }
> > @@ -5896,12 +5926,11 @@ 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 +5941,9 @@ 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 +7629,7 @@ 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,
> > @@ -8086,7 +8118,7 @@ static struct l2cap_chan *l2cap_global_fixed_chan(struct l2cap_chan *c,
> >               if (src_type != c->src_type)
> >                       continue;
> >
> > -             l2cap_chan_hold(c);
> > +             c = l2cap_chan_hold_unless_zero(c);
> >               read_unlock(&chan_list_lock);
> >               return c;
> >       }
>
>
> --
> Lee Jones [李琼斯]
> Principal Technical Lead - Developer Services
> Linaro.org │ Open source software for Arm SoCs
> Follow Linaro: Facebook | Twitter | Blog



-- 
Luiz Augusto von Dentz

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