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

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Date:   Mon, 29 Oct 2018 15:58:19 +0100
From:   Christian Brauner <christian@...uner.io>
To:     keescook@...omium.org, linux-kernel@...r.kernel.org
Cc:     ebiederm@...ssion.com, mcgrof@...nel.org,
        akpm@...ux-foundation.org, joe.lawrence@...hat.com,
        longman@...hat.com, linux@...inikbrodowski.net,
        viro@...iv.linux.org.uk, adobriyan@...il.com,
        linux-api@...r.kernel.org
Subject: Re: [PATCH v3 0/2] sysctl: handle overflow for file-max

On Wed, Oct 17, 2018 at 12:33:20AM +0200, Christian Brauner wrote:
> Hey,
> 
> Here is v3 of this patchset. Changelogs are in the individual commits.
> 
> 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.)

Just so that we don't forget, can we make sure that this gets picked
into linux-next? :)

Christian

> 
> 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
>