mac80211: do not wake queues on a vif that is being stopped

When a vif is being removed and sdata->bss is cleared, __ieee80211_wake_txqs
can still be called on it, which crashes as soon as sdata->bss is being
dereferenced.
To fix this properly, check for SDATA_STATE_RUNNING before waking queues,
and take the fq lock when setting it (to ensure that __ieee80211_wake_txqs
observes the change when running on a different CPU

Signed-off-by: Felix Fietkau <nbd@nbd.name>
---
 net/mac80211/iface.c | 2 ++
 net/mac80211/util.c  | 3 +++
 2 files changed, 5 insertions(+)

Felix Fietkau <nbd@nbd.name> writes:

> When a vif is being removed and sdata->bss is cleared, __ieee80211_wake_txqs
> can still be called on it, which crashes as soon as sdata->bss is being
> dereferenced.
> To fix this properly, check for SDATA_STATE_RUNNING before waking queues,
> and take the fq lock when setting it (to ensure that __ieee80211_wake_txqs
> observes the change when running on a different CPU
>
> Signed-off-by: Felix Fietkau <nbd@nbd.name>

I think it's a little ugly to expand usage of fq.lock across more and
more places, I don't really have a good alternative, so:

Acked-by: Toke Høiland-Jørgensen <toke@kernel.org>

On 5/31/22 12:08 PM, Felix Fietkau wrote:
> When a vif is being removed and sdata->bss is cleared, __ieee80211_wake_txqs
> can still be called on it, which crashes as soon as sdata->bss is being
> dereferenced.
> To fix this properly, check for SDATA_STATE_RUNNING before waking queues,
> and take the fq lock when setting it (to ensure that __ieee80211_wake_txqs
> observes the change when running on a different CPU

I patched this into my 5.17+ kernel, and in a test that brings up 16 virtual
station vdevs on an mtk7915, 4 of them on each of two radios will not associate.
They get 4-way timeouts.

So, I think there must be something wrong with assumptions in this patch, or
maybe it depends on some other patch I am missing.  I'll remove it from my tree...

Thanks,
Ben

> 
> Signed-off-by: Felix Fietkau <nbd@nbd.name>
> ---
>   net/mac80211/iface.c | 2 ++
>   net/mac80211/util.c  | 3 +++
>   2 files changed, 5 insertions(+)
> 
> diff --git a/net/mac80211/iface.c b/net/mac80211/iface.c
> index 41531478437c..15a73b7fdd75 100644
> --- a/net/mac80211/iface.c
> +++ b/net/mac80211/iface.c
> @@ -377,7 +377,9 @@ static void ieee80211_do_stop(struct ieee80211_sub_if_data *sdata, bool going_do
>   	bool cancel_scan;
>   	struct cfg80211_nan_func *func;
>   
> +	spin_lock_bh(&local->fq.lock);
>   	clear_bit(SDATA_STATE_RUNNING, &sdata->state);
> +	spin_unlock_bh(&local->fq.lock);
>   
>   	cancel_scan = rcu_access_pointer(local->scan_sdata) == sdata;
>   	if (cancel_scan)
> diff --git a/net/mac80211/util.c b/net/mac80211/util.c
> index 1e26b5235add..dad42d42aa84 100644
> --- a/net/mac80211/util.c
> +++ b/net/mac80211/util.c
> @@ -301,6 +301,9 @@ static void __ieee80211_wake_txqs(struct ieee80211_sub_if_data *sdata, int ac)
>   	local_bh_disable();
>   	spin_lock(&fq->lock);
>   
> +	if (!test_bit(SDATA_STATE_RUNNING, &sdata->state))
> +		goto out;
> +
>   	if (sdata->vif.type == NL80211_IFTYPE_AP)
>   		ps = &sdata->bss->ps;
>   
>