linux-kernel - Re: [PATCH][next] cpumask: allocate enough space for string and trailing '\0' char

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Message-ID: <431c72da-1f85-ed4f-1023-08c844d572ac@canonical.com>
Date:   Tue, 10 Nov 2020 19:07:37 +0000
From:   Colin Ian King <colin.king@...onical.com>
To:     paulmck@...nel.org
Cc:     Paul Gortmaker <paul.gortmaker@...driver.com>,
        Qian Cai <cai@...hat.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org,
        Linux Next Mailing List <linux-next@...r.kernel.org>
Subject: Re: [PATCH][next] cpumask: allocate enough space for string and
 trailing '\0' char

On 10/11/2020 18:38, Paul E. McKenney wrote:
> On Tue, Nov 10, 2020 at 03:34:05PM +0000, Colin Ian King wrote:
>> On 10/11/2020 15:24, Paul E. McKenney wrote:
>>> On Mon, Nov 09, 2020 at 11:57:15PM -0500, Paul Gortmaker wrote:
>>>>
>>>>
>>>> On 2020-11-09 8:07 p.m., Qian Cai wrote:
>>>>> On Mon, 2020-11-09 at 13:04 +0000, Colin King wrote:
>>>>>> From: Colin Ian King <colin.king@...onical.com>
>>>>>>
>>>>>> Currently the allocation of cpulist is based on the length of buf but does
>>>>>> not include the addition end of string '\0' terminator. Static analysis is
>>>>>> reporting this as a potential out-of-bounds access on cpulist. Fix this by
>>>>>> allocating enough space for the additional '\0' terminator.
>>>>>>
>>>>>> Addresses-Coverity: ("Out-of-bounds access")
>>>>>> Fixes: 65987e67f7ff ("cpumask: add "last" alias for cpu list specifications")
>>>>>
>>>>> Yeah, this bad commit also introduced KASAN errors everywhere and then will
>>>>> disable lockdep that makes our linux-next CI miserable. Confirmed that this
>>>>> patch will fix it.
>>>>
>>>> I appreciate the reports reminding me why I hate touching string handling.
>>>>
>>>> But let us not lose sight of why linux-next exists.  We want to
>>>> encourage code to appear there as a sounding board before it goes
>>>> mainline, so we can fix things and not pollute mainline git history
>>>> with those trivialities.
>>>>
>>>> If you've decided to internalize linux-next as part of your CI, then
>>>> great, but do note that does not elevate linux-next to some pristine
>>>> status for the world at large.  That only means you have to watch more
>>>> closely what is going on.
>>>>
>>>> If you want to declare linux-next unbreakable -- well that would scare
>>>> away others to get the multi-arch or multi-config coverage that they may
>>>> not be able to do themselves.  We are not going to do that.
>>>>
>>>> I have (hopefully) fixed the "bad commit" in v2 -- as part of the
>>>> implicit linux-next rule "you broke it, you better fix it ASAP".
>>>>
>>>> But "bad" and "miserable" can be things that might scare people off of
>>>> making use of linux-next for what it is meant to be for.  And I am not
>>>> OK with that.
>>>
>>> They would need to use much stronger language to scare me off.  That said,
>>> what on earth is the point of running tests if they do not from time to
>>> time find bugs?  ;-)
>>
>> For me, part of the QA process is statically analyzing linux-next to
>> catch bugs before they land in linux. I think other testing is equally
>> worth while as catching bugs early saves time and money.
> 
> All kidding aside, the fact that this appeared in -next was due to a
> mistake on my part, namely failing to push the changes before starting
> the test.  Please accept my apologies, and I will continue to do my
> best to avoid this sort of thing.
> 
> 							Thanx, Paul

No problem. I'm glad we have tools to catch issues like this.

Colin

> 
>> Colin
>>
>>>
>>>> Thanks,
>>>> Paul.
>>>> --
>>>>
>>>>>
>>>>>> Signed-off-by: Colin Ian King <colin.king@...onical.com>
>>>>>> ---
>>>>>>   lib/cpumask.c | 2 +-
>>>>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/lib/cpumask.c b/lib/cpumask.c
>>>>>> index 34ecb3005941..cb8a3ef0e73e 100644
>>>>>> --- a/lib/cpumask.c
>>>>>> +++ b/lib/cpumask.c
>>>>>> @@ -185,7 +185,7 @@ int __ref cpulist_parse(const char *buf, struct cpumask
>>>>>> *dstp)
>>>>>>   {
>>>>>>   	int r;
>>>>>>   	char *cpulist, last_cpu[5];	/* NR_CPUS <= 9999 */
>>>>>> -	size_t len = strlen(buf);
>>>>>> +	size_t len = strlen(buf) + 1;
>>>>>>   	bool early = !slab_is_available();
>>>>>>   	if (!strcmp(buf, "all")) {
>>>>>
>>