Re: [PATCH v3 0/2] sysctl: handle overflow for file-max

[Kees Cook]

On Tue, Oct 16, 2018 at 3:33 PM, Christian Brauner <christian@xxxxxxxxxx> wrote:
> Hey,
>
> Here is v3 of this patchset. Changelogs are in the individual commits.

Thanks! These look good. Andrew, can you take these?

-Kees

>
> Currently, when writing
>
> echo 18446744073709551616 > /proc/sys/fs/file-max
>
> /proc/sys/fs/file-max will overflow and be set to 0. That quickly
> crashes the system.
>
> The first version of this patch intended to detect the overflow and cap
> at ULONG_MAX. However, we should not do this and rather return EINVAL on
> overflow. The reasons are:
> - this aligns with other sysctl handlers that simply reject overflows
>   (cf. [1], [2], and a bunch of others)
> - we already do a partial fail on overflow right now
>   Namely, when the TMPBUFLEN is exceeded. So we already reject values
>   such as 184467440737095516160 (21 chars) but accept values such as
>   18446744073709551616 (20 chars) but both are overflows. So we should
>   just always reject 64bit overflows and not special-case this based on
>   the number of chars.
>
> (This patchset is in reference to https://lkml.org/lkml/2018/10/11/585.)
>
> Thanks!
> Christian
>
> [1]: fb910c42cceb ("sysctl: check for UINT_MAX before unsigned int min/max")
> [2]: 196851bed522 ("s390/topology: correct topology mode proc handler")
>
> Christian Brauner (2):
>   sysctl: handle overflow in proc_get_long
>   sysctl: handle overflow for file-max
>
>  kernel/sysctl.c | 47 ++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 46 insertions(+), 1 deletion(-)
>
> --
> 2.17.1
>



-- 
Kees Cook
Pixel Security