linux-kernel - Re: [PATCH] sched/core: check format and overflows in cgroup2 cpu.max

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Date:   Tue, 5 Mar 2019 20:03:24 +0300
From:   Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:     Tejun Heo <tj@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>, cgroups@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] sched/core: check format and overflows in cgroup2 cpu.max

On 05.03.2019 18:57, Tejun Heo wrote:
> Hello,
> 
> On Wed, Feb 27, 2019 at 11:13:21AM +0300, Konstantin Khlebnikov wrote:
>> Cgroup2 interface for cpu bandwidth limit has some flaws:
>>
>> - on stack buffer overflow
>> - no checks for valid format or trailing garbage
>> - no checks for integer overflows
>>
>> This patch fixes all these flaws.
> 
> Ditto as the blkio patch.  Unless there is a correctness problem, my
> preference is towards keeping the parsing functions simple and I don't
> think the kernel needs to play the role of strict input verifier here
> as long as the only foot getting shot is the user's own.

IMHO non-strict interface more likely hides bugs and could cause problems for future changes.

Here is only only one fatal bug - buffer overflow in sscanf because %s has no limit.

Strict validation could be done as more strict sscanf variant or some kind of extension for format string.

> 
> Thanks.
>