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

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Message-ID: <6050d075-52cc-d1b8-51c4-4d0dac62a42e@canonical.com>
Date:   Tue, 10 Nov 2020 15:34:05 +0000
From:   Colin Ian King <colin.king@...onical.com>
To:     paulmck@...nel.org, Paul Gortmaker <paul.gortmaker@...driver.com>
Cc:     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 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?  ;-)
> 
> 							Thanx, Paul

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.

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")) {
>>>