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

[Konstantin Khlebnikov]

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.