netdev - bug report: iwlwifi: mvm: support mac80211 TXQs model

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Message-ID: <427786ae-159a-a7d1-2334-46656d3f2b51@canonical.com>
Date:   Wed, 20 Feb 2019 14:40:08 +0000
From:   Colin Ian King <colin.king@...onical.com>
To:     Sara Sharon <sara.sharon@...el.com>,
        Johannes Berg <johannes.berg@...el.com>,
        Emmanuel Grumbach <emmanuel.grumbach@...el.com>,
        Luca Coelho <luciano.coelho@...el.com>,
        Intel Linux Wireless <linuxwifi@...el.com>,
        Sara Sharon <sara.sharon@...el.com>,
        "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
        netdev@...r.kernel.org
Cc:     Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: bug report: iwlwifi: mvm: support mac80211 TXQs model

Hi,

Static analysis by CoverityScan has detected an uninitialized variable
error in drivers/net/wireless/intel/iwlwifi/mvm/mac-ctxt.c

Variable used_hw_queues in iwl_mvm_mac_ctxt_init() is no longer being
assigned an initial value, causing garbage to be found when calling
find_first_zero_bit() on used_hw_queues.

CoverityScan reports this as follows:

363        for (ac = 0; ac < IEEE80211_NUM_ACS; ac++) {
   CID 1477001 (#1 of 1): Uninitialized scalar variable (UNINIT)
uninit_use_in_call: Using uninitialized value used_hw_queues when
calling find_first_zero_bit.

364                u8 queue = find_first_zero_bit(&used_hw_queues,
queue_limit);
365

This issue was caused by the following commit:

cfbc6c4c5b91c7725ef14465b98ac347d31f2334 ("iwlwifi: mvm: support
mac80211 TXQs model")

..when the used_hw_queues initialization was removed:

@@ -360,8 +300,6 @@ int iwl_mvm_mac_ctxt_init(struct iwl_mvm *mvm,
struct ieee80211_vif *vif)
                mvm->hw, IEEE80211_IFACE_ITER_RESUME_ALL,
                iwl_mvm_mac_iface_iterator, &data);

-       used_hw_queues = iwl_mvm_get_used_hw_queues(mvm, vif);
-
        /*
         * In the case we're getting here during resume, it's similar to
         * firmware restart, and with RESUME_ALL the iterator will find


I'm not 100% sure if the right thing to do is just to now initialize
used_hw_queues to zero; it's not entirely clear what the initial value
should be now.

Colin