Re: [PATCH] net/mac80211/agg-rx.c: fix use of uninitialised values

From: Julian Calaby
Date: Thu Jan 28 2016 - 05:12:13 EST

Hi Johannes,

On Thu, Jan 28, 2016 at 8:48 PM, Johannes Berg
<johannes@xxxxxxxxxxxxxxxx> wrote:
> On Thu, 2016-01-28 at 10:27 +1100, Julian Calaby wrote:
>> I'd prefer to just set ->removed to false right after we set
>> ->auto_seq as that should be faster, however I don't know if
>> __ieee80211_start_rx_ba_session() is a fast path so I don't know if
>> this is saving anything.
> It's not supposed to be called frequently, no.

Then most of my commentary is moot.

I guess the argument comes down to do we zero everything or initialise
everything, and if speed isn't an issue, the former is better.

>> On another note, this is an error that should be pretty easy to spot.
>> Could any of the automated tools find cases where a struct containing
>> a bool variable is kmalloc'd and returned without assigning all the
>> bools?
> I think you'd quickly drown in false positives, since "return" isn't
> necessarily something that means it needs to have been fully
> initialized.


Either way, I'm guessing that UBSAN will pick up a lot of similar bugs
and the output of that is probably a much smaller haystack to dig
through than just "every" kmalloc() call.


Julian Calaby

Email: julian.calaby@xxxxxxxxx