Hi Dan,
On Thu, Jul 19, 2012 at 1:33 PM, Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote:
> Hello Helmut Schaa,
>
> I'm going through some old static checker warnings and I was concerned
> about this one:
>
> The patch 55b585e29095: "rt2x00: Don't call ieee80211_get_tx_rate for
> MCS rates" from Mar 3, 2011, leads to the following warning:
> drivers/net/wireless/rt2x00/rt2x00queue.c:508
> rt2x00queue_create_tx_descriptor()
> error: potential NULL dereference 'hwrate'.
>
> 482 /*
> 483 * Determine rate modulation.
> 484 */
> 485 if (txrate->flags & IEEE80211_TX_RC_GREEN_FIELD)
> 486 txdesc->rate_mode = RATE_MODE_HT_GREENFIELD;
>
> hwrate is NULL here.
>
> 487 else if (txrate->flags & IEEE80211_TX_RC_MCS)
> 488 txdesc->rate_mode = RATE_MODE_HT_MIX;
> 489 else {
> 490 rate = ieee80211_get_tx_rate(rt2x00dev->hw, tx_info);
> 491 hwrate = rt2x00_get_rate(rate->hw_value);
> 492 if (hwrate->flags & DEV_RATE_OFDM)
> 493 txdesc->rate_mode = RATE_MODE_OFDM;
> 494 else
> 495 txdesc->rate_mode = RATE_MODE_CCK;
> 496 }
> 497
> 498 /*
> 499 * Apply TX descriptor handling by components
> 500 */
> 501 rt2x00crypto_create_tx_descriptor(rt2x00dev, skb, txdesc);
> 502 rt2x00queue_create_tx_descriptor_seq(rt2x00dev, skb, txdesc);
> 503
> 504 if (test_bit(REQUIRE_HT_TX_DESC, &rt2x00dev->cap_flags))
> 505 rt2x00queue_create_tx_descriptor_ht(rt2x00dev, skb, txdesc,
> 506 hwrate);
>
> On this path we dereference dereference hwrate if IEEE80211_TX_RC_MCS is
> not set, but we don't check for IEEE80211_TX_RC_GREEN_FIELD.
Right, I guess the basic assumption is that IEEE80211_TX_RC_GREEN_FIELD is
only used in conjunction with IEEE80211_TX_RC_MCS.
>
> 507 else
> 508 rt2x00queue_create_tx_descriptor_plcp(rt2x00dev, skb, txdesc,
> 509 hwrate);
>
> On this patch we dereference hwrate unconditionally.
mac80211 should never request a MCS rate for devices that don't register
MCS rate support.
I think we could make the static checker happy by moving the hwrate
dereferencing
into rt2x00queue_create_tx_descriptor_plcp and
rt2x00queue_create_tx_descriptor_ht?
Any better ideas?
Helmut
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