Re: [PATCH v4 0/3] net: sysctl: Const Qualify sysctl ctl_table arrays

[Simon Horman]

On Mon, Aug 10, 2026 at 03:01:01PM +0200, Joel Granados wrote:
> What?
> =====
> We do two things:
> 1. Reject netns-unsafe: Replace warning and file permission change with
>    an error (reject registration) when an "unsafe" net sysctl
>    registration is detected.
> 2. Const qualify: Const qualify network templated ctl_table arrays and
>    unconditional kmemdup'ed ctl_table arrays.
> 
> Why?
> ====
> The main motivation for this is to continue with the const qualification
> of the ctl_table arrays [1]. The permission change inside
> ensure_safe_net_sysctl disallows cons qualifiaction as it basically
> modifies the entries before running the sysctl registration.
> 
>       ent->mode &= ~0222;
> 
> On reject netns-unsafe?
> =======================
> * I believe that there is currently now way that the permission change
>   gets executed [2]
> * I found one case where the warning message was posted to lore
>   (vsock_sysctl_register) [3], but it made its to mainline as part of
>   the second case in [2].
> * We should error anyway because writing to the global sysctl value
>   through a child netns is indicative of a bug [4].
> 
> On Const qualification?
> =======================
> We can separate the places where network registers sysctl tables into
> three groups:
> 1. Static global: The unchanged global static arrays are passed along to
>    sysctl register.
> 2. Always kmemdup: The global static arrays are always kmemdup'ed before
>    passing them along to sysctl register.
> 3. Dynamic global: The global static array is changed in place before
>    passing it along to sysctl register.
> 
> This series handles case 1 and 2. It leaves 3 for a later point as
> const qualifying those global ctl_tables is more involved.
> 
> I would be very thankful if you point me to anything that I have missed
> in my analysis that shows that this cannot/shouldn't be done.

For the series:

Reviewed-by: Simon Horman <horms@xxxxxxxxxx>