Re: [PATCH v2] mac80211: fix race in ieee80211_register_hw()

[Sumit Garg]

Hi Johannes,

On Wed, 8 Apr 2020 at 00:55, Krishna Chaitanya <chaitanya.mgit@xxxxxxxxx> wrote:
>
> On Tue, Apr 7, 2020 at 3:41 PM Sumit Garg <sumit.garg@xxxxxxxxxx> wrote:
> >
> > A race condition leading to a kernel crash is observed during invocation
> > of ieee80211_register_hw() on a dragonboard410c device having wcn36xx
> > driver built as a loadable module along with a wifi manager in user-space
> > waiting for a wifi device (wlanX) to be active.
> >
> > Sequence diagram for a particular kernel crash scenario:
> >
> >     user-space  ieee80211_register_hw()  ieee80211_tasklet_handler()
> >     ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >        |                    |                 |
> >        |<---phy0----wiphy_register()          |
> >        |-----iwd if_add---->|                 |
> just a nitpick, a better one would be (iwd: if_add + ap_start) since
> we need to have 'iwctl ap start'
> to trigger the interrupts.
> >        |                    |<---IRQ----(RX packet)
> >        |              Kernel crash            |
> >        |              due to unallocated      |
> >        |              workqueue.              |
> >        |                    |                 |
> >        |       alloc_ordered_workqueue()      |
> >        |                    |                 |
> >        |              Misc wiphy init.        |
> >        |                    |                 |
> >        |            ieee80211_if_add()        |
> >        |                    |                 |
> >
> > As evident from above sequence diagram, this race condition isn't specific
> > to a particular wifi driver but rather the initialization sequence in
> > ieee80211_register_hw() needs to be fixed. So re-order the initialization
> > sequence and the updated sequence diagram would look like:
> >
> >     user-space  ieee80211_register_hw()  ieee80211_tasklet_handler()
> >     ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >        |                    |                 |
> >        |       alloc_ordered_workqueue()      |
> >        |                    |                 |
> >        |              Misc wiphy init.        |
> >        |                    |                 |
> >        |<---phy0----wiphy_register()          |
> >        |-----iwd if_add---->|                 |
> same as above.
> >        |                    |<---IRQ----(RX packet)
> >        |                    |                 |
> >        |            ieee80211_if_add()        |
> >        |                    |                 |
> >
> > Cc: <stable@xxxxxxxxxxxxxxx>
> > Signed-off-by: Sumit Garg <sumit.garg@xxxxxxxxxx>
> > ---
> >

In case we don't have any further comments, could you fix this nitpick
from Chaitanya while applying or would you like me to respin and send
v3?

-Sumit

> > Changes in v2:
> > - Move rtnl_unlock() just after ieee80211_init_rate_ctrl_alg().
> > - Update sequence diagrams in commit message for more clarification.
> >
> >  net/mac80211/main.c | 22 +++++++++++++---------
> >  1 file changed, 13 insertions(+), 9 deletions(-)
> >
> > diff --git a/net/mac80211/main.c b/net/mac80211/main.c
> > index 4c2b5ba..d497129 100644
> > --- a/net/mac80211/main.c
> > +++ b/net/mac80211/main.c
> > @@ -1051,7 +1051,7 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)
> >                 local->hw.wiphy->signal_type = CFG80211_SIGNAL_TYPE_UNSPEC;
> >                 if (hw->max_signal <= 0) {
> >                         result = -EINVAL;
> > -                       goto fail_wiphy_register;
> > +                       goto fail_workqueue;
> >                 }
> >         }
> >
> > @@ -1113,7 +1113,7 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)
> >
> >         result = ieee80211_init_cipher_suites(local);
> >         if (result < 0)
> > -               goto fail_wiphy_register;
> > +               goto fail_workqueue;
> >
> >         if (!local->ops->remain_on_channel)
> >                 local->hw.wiphy->max_remain_on_channel_duration = 5000;
> > @@ -1139,10 +1139,6 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)
> >
> >         local->hw.wiphy->max_num_csa_counters = IEEE80211_MAX_CSA_COUNTERS_NUM;
> >
> > -       result = wiphy_register(local->hw.wiphy);
> > -       if (result < 0)
> > -               goto fail_wiphy_register;
> > -
> >         /*
> >          * We use the number of queues for feature tests (QoS, HT) internally
> >          * so restrict them appropriately.
> > @@ -1207,6 +1203,8 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)
> >                 goto fail_rate;
> >         }
> >
> > +       rtnl_unlock();
> > +
> >         if (local->rate_ctrl) {
> >                 clear_bit(IEEE80211_HW_SUPPORTS_VHT_EXT_NSS_BW, hw->flags);
> >                 if (local->rate_ctrl->ops->capa & RATE_CTRL_CAPA_VHT_EXT_NSS_BW)
> > @@ -1254,6 +1252,12 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)
> >                 local->sband_allocated |= BIT(band);
> >         }
> >
> > +       result = wiphy_register(local->hw.wiphy);
> > +       if (result < 0)
> > +               goto fail_wiphy_register;
> > +
> > +       rtnl_lock();
> > +
> >         /* add one default STA interface if supported */
> >         if (local->hw.wiphy->interface_modes & BIT(NL80211_IFTYPE_STATION) &&
> >             !ieee80211_hw_check(hw, NO_AUTO_VIF)) {
> > @@ -1293,6 +1297,8 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)
> >  #if defined(CONFIG_INET) || defined(CONFIG_IPV6)
> >   fail_ifa:
> >  #endif
> > +       wiphy_unregister(local->hw.wiphy);
> > + fail_wiphy_register:
> >         rtnl_lock();
> >         rate_control_deinitialize(local);
> >         ieee80211_remove_interfaces(local);
> > @@ -1302,8 +1308,6 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)
> >         ieee80211_led_exit(local);
> >         destroy_workqueue(local->workqueue);
> >   fail_workqueue:
> > -       wiphy_unregister(local->hw.wiphy);
> > - fail_wiphy_register:
> >         if (local->wiphy_ciphers_allocated)
> >                 kfree(local->hw.wiphy->cipher_suites);
> >         kfree(local->int_scan_req);
> > @@ -1353,8 +1357,8 @@ void ieee80211_unregister_hw(struct ieee80211_hw *hw)
> >         skb_queue_purge(&local->skb_queue_unreliable);
> >         skb_queue_purge(&local->skb_queue_tdls_chsw);
> >
> > -       destroy_workqueue(local->workqueue);
> >         wiphy_unregister(local->hw.wiphy);
> > +       destroy_workqueue(local->workqueue);
> >         ieee80211_led_exit(local);
> >         kfree(local->int_scan_req);
> >  }
> > --
> > 2.7.4
> >
>
>
> --
> Thanks,
> Regards,
> Chaitanya T K.