linux-kernel - Re: [PATCH] mac80211: initialize variable have_higher_than

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Message-ID: <b3ef8d23-7c77-7c83-0bc8-2054b7ac1d8b@redhat.com>
Date:   Fri, 24 Dec 2021 06:01:27 -0800
From:   Tom Rix <trix@...hat.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     johannes@...solutions.net, davem@...emloft.net, kuba@...nel.org,
        nathan@...nel.org, linville@...driver.com,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] mac80211: initialize variable have_higher_than_11mbit


On 12/23/21 12:30 PM, Nick Desaulniers wrote:
> On Thu, Dec 23, 2021 at 8:29 AM <trix@...hat.com> wrote:
>> From: Tom Rix <trix@...hat.com>
>>
>> Clang static analysis reports this warnings
>>
>> mlme.c:5332:7: warning: Branch condition evaluates to a
>>    garbage value
>>      have_higher_than_11mbit)
>>      ^~~~~~~~~~~~~~~~~~~~~~~
>>
>> have_higher_than_11mbit is only set to true some of the time in
>> ieee80211_get_rates() but is checked all of the time.  So
>> have_higher_than_11mbit needs to be initialized to false.
> LGTM. There's only one caller of ieee80211_get_rates() today; if there
> were others, they could make a similar mistake in the future. An
> alternate approach: ieee80211_get_rates() could unconditionally write
> false before the loop that could later write true. Then call sites
> don't need to worry about this conditional assignment. Perhaps that
> would be preferable? If not:

The have_higher_than_11mbit variable had previously be initialized to false.

The commit 5d6a1b069b7f moved the variable without initializing.

Tom

>
> Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
>
>> Fixes: 5d6a1b069b7f ("mac80211: set basic rates earlier")
>> Signed-off-by: Tom Rix <trix@...hat.com>
>> ---
>>   net/mac80211/mlme.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/net/mac80211/mlme.c b/net/mac80211/mlme.c
>> index 51f55c4ee3c6e..766cbbc9c3a72 100644
>> --- a/net/mac80211/mlme.c
>> +++ b/net/mac80211/mlme.c
>> @@ -5279,7 +5279,7 @@ static int ieee80211_prep_connection(struct ieee80211_sub_if_data *sdata,
>>           */
>>          if (new_sta) {
>>                  u32 rates = 0, basic_rates = 0;
>> -               bool have_higher_than_11mbit;
>> +               bool have_higher_than_11mbit = false;
>>                  int min_rate = INT_MAX, min_rate_index = -1;
>>                  const struct cfg80211_bss_ies *ies;
>>                  int shift = ieee80211_vif_get_shift(&sdata->vif);
>> --
>> 2.26.3
>>
>