From: Johannes Berg <johannes@sipsolutions.net>
To: Jiri Slaby <jslaby@suse.cz>,
Emmanuel Grumbach <emmanuel.grumbach@intel.com>,
luciano.coelho@intel.com, linuxwifi@intel.com,
Kalle Valo <kvalo@codeaurora.org>,
linux-wireless@vger.kernel.org,
ML netdev <netdev@vger.kernel.org>,
Linux kernel mailing list <linux-kernel@vger.kernel.org>
Subject: Re: [UBSAN] iwlmvm's iwl_mvm_enable_txq accesses IEEE80211_INVAL_HW_QUEUE
Date: Fri, 23 Jun 2017 09:58:55 +0200 [thread overview]
Message-ID: <1498204735.2595.1.camel@sipsolutions.net> (raw)
In-Reply-To: <3f089134-9739-a61f-80e4-6f9ee7dd83b4@suse.cz> (sfid-20170623_094852_912665_18314A6E)
On Fri, 2017-06-23 at 09:48 +0200, Jiri Slaby wrote:
>
> mac80211_queue is 255 which is IEEE80211_INVAL_HW_QUEUE, so it should
> not be worked with at all.
Funny you should find this today :-)
> The invalid queue is hopefully handled in ieee80211_check_queues
> after
> drv_add_interface in ieee80211_do_open:
>
> res = drv_add_interface(local, sdata);
> if (res)
> goto err_stop;
> res = ieee80211_check_queues(sdata,
> ieee80211_vif_type_p2p(&sdata->vif));
>
>
> But the mvm driver still should not blindly shift 1 by 255 in
> iwl_mvm_enable_txq. Should the check for the invalid queue be before
> adding the interface in mac80211? Or should drivers check it in their
> add_interface?
Everything is actually handled well afaict, because the bug won't
matter - this is a queue we'll never really stop, so we won't be
looking at the (invalid) result of the calculation. I had actually been
under the impression that it wasn't undefined but would just result in
0; that's clearly not true but also doesn't matter. AFAICT it even
results in 0x80000000 (which makes some sense, since 255 % 32 == 31),
and that's a queue number (31) that's too big for mac80211 anyway, so
it would warn if we were to ever try to stop it.
In later versions of the code, however, there *was* indeed a bug - we
were using a u8 instead of a u32 in the code we have internally. While
fixing *that* bug, I also made this catch the case of
IEEE80211_INVAL_HW_QUEUE so we'll not modify the bitmap at all, which
is the correct thing to do.
IOW - yes, it's not nice, but it also shouldn't matter, and even if for
some strange reason we tried to stop the queue we'd just get a warning
from mac80211.
johannes
prev parent reply other threads:[~2017-06-23 7:59 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-23 7:48 [UBSAN] iwlmvm's iwl_mvm_enable_txq accesses IEEE80211_INVAL_HW_QUEUE Jiri Slaby
2017-06-23 7:58 ` Johannes Berg [this message]
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