On Friday, January 12, 2018 7:39:50 PM CET Dan Williams wrote:

On Fri, Jan 12, 2018 at 6:42 AM, Christian Lamparter [off-list ref] wrote:

quoted

On Friday, January 12, 2018 1:47:46 AM CET Dan Williams wrote:

quoted

Static analysis reports that 'queue' may be a user controlled value that
is used as a data dependency to read from the 'ar9170_qmap' array. In
order to avoid potential leaks of kernel memory values, block
speculative execution of the instruction stream that could issue reads
based on an invalid result of 'ar9170_qmap[queue]'. In this case the
value of 'ar9170_qmap[queue]' is immediately reused as an index to the
'ar->edcf' array.

Based on an original patch by Elena Reshetova.

Cc: Christian Lamparter <chunkeey@googlemail.com>
Cc: Kalle Valo <redacted>
Cc: linux-wireless@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Dan Williams <redacted>
---

This patch (and p54, cw1200) look like the same patch?!
Can you tell me what happend to:

On Saturday, January 6, 2018 5:34:03 PM CET Dan Williams wrote:

quoted

On Sat, Jan 6, 2018 at 6:23 AM, Christian Lamparter [off-list ref] wrote:

quoted

And Furthermore a invalid queue (param->ac) would cause a crash in
this line in mac80211 before it even reaches the driver [1]:
|       sdata->tx_conf[params->ac] = p;
|                   ^^^^^^^^
|       if (drv_conf_tx(local, sdata, >>>> params->ac <<<<, &p)) {
|        ^^ (this is a wrapper for the *_op_conf_tx)

I don't think these chin-up exercises are needed.

Quite the contrary, you've identified a better place in the call stack
to sanitize the input and disable speculation. Then we can kill the
whole class of the wireless driver reports at once it seems.

<https://www.spinics.net/lists/netdev/msg476353.html>

I didn't see where ac is being validated against the driver specific
'queues' value in that earlier patch.

The link to the check is right there in the earlier post. It's in 
parse_txq_params():
<https://github.com/torvalds/linux/blob/master/net/wireless/nl80211.c#L2070>
|	if (txq_params->ac >= NL80211_NUM_ACS)
|		return -EINVAL;

NL80211_NUM_ACS is 4
<http://elixir.free-electrons.com/linux/v4.15-rc7/source/include/uapi/linux/nl80211.h#L3748>

This check was added ever since mac80211's ieee80211_set_txq_params():
| sdata->tx_conf[params->ac] = p;

For cw1200: the driver just sets the dev->queue to 4.
In carl9170 dev->queues is set to __AR9170_NUM_TXQ and
p54 uses P54_QUEUE_AC_NUM.

Both __AR9170_NUM_TXQ and P54_QUEUE_AC_NUM are 4.
And this is not going to change since all drivers
have to follow mac80211's queue API:
<https://wireless.wiki.kernel.org/en/developers/documentation/mac80211/queues>

Some background:
In the old days (linux 2.6 and early 3.x), the parse_txq_params() function did
not verify the "queue" value. That's why these drivers had to do it.

Here's the relevant code from 2.6.39:
<http://elixir.free-electrons.com/linux/v2.6.39/source/net/wireless/nl80211.c#L879>
You'll notice that the check is missing there.
Here's mac80211's ieee80211_set_txq_params for reference:
<http://elixir.free-electrons.com/linux/v2.6.39/source/net/mac80211/cfg.c#L1197>

However over time, the check in the driver has become redundant.

quoted

Anyway, I think there's an easy way to solve this: remove the
"if (queue < ar->hw->queues)" check altogether. It's no longer needed
anymore as the "queue" value is validated long before the driver code
gets called.

And from my understanding, this will fix the "In this case
the value of 'ar9170_qmap[queue]' is immediately reused as an index to
the 'ar->edcf' array." gripe your tool complains about.

This is here's a quick test-case for carl9170.:
---

diff --git a/drivers/net/wireless/ath/carl9170/main.c b/drivers/net/wireless/ath/carl9170/main.c
index 988c8857d78c..2d3afb15bb62 100644
--- a/drivers/net/wireless/ath/carl9170/main.c
+++ b/drivers/net/wireless/ath/carl9170/main.c

@@ -1387,13 +1387,8 @@ static int carl9170_op_conf_tx(struct ieee80211_hw *hw,
        int ret;

        mutex_lock(&ar->mutex);
-       if (queue < ar->hw->queues) {
-               memcpy(&ar->edcf[ar9170_qmap[queue]], param, sizeof(*param));
-               ret = carl9170_set_qos(ar);
-       } else {
-               ret = -EINVAL;
-       }
-
+       memcpy(&ar->edcf[ar9170_qmap[queue]], param, sizeof(*param));
+       ret = carl9170_set_qos(ar);
        mutex_unlock(&ar->mutex);
        return ret;
 }

---
What does your tool say about this?

If you take away the 'if' then I don't the tool will report on this.

quoted

(If necessary, the "queue" value could be even sanitized with a
queue %= ARRAY_SIZE(ar9170_qmap); before the mutex_lock.)

That is what array_ptr() is doing in a more sophisticated way.

I think it's a very roundabout way :D. In any case the queue %= ...
could also be replaced by:
BUILD_BUG_ON(ARRAY_SIZE(ar9170_qmap) != NL80211_NUM_ACS));
(And the equivalent for p54, cw1200)