Re: [PATCH v2 0/4] sysctl: Disallow partial updates of miss-formatted sysctl vectors

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 14 Aug 2026 12:41:11 +0200 Joel Granados <joel.granados@kernel.org> wrote:

> What?
> =====
> 
> Stage table->data when writing INT & ULONG ctl_tables. Commit staged
> data to kernel variable only when all the conversions have succeeded.
> This is applicable only to variables that represent a vector; paths
> pertaining to scalers are left unchanged. Notice that partial updates

"scalars"

> can still happen if less than the size of the vector are passed and
> correctly formatted.
> 
> This is the behavior we are protecting against:
> 
>   # echo "4 4 1 7" > /proc/sys/kernel/printk
>   # echo "1 x" > /proc/sys/kernel/printk
>   -bash: echo: write error: Invalid argument
>   # cat /proc/sys/kernel/printk
>   1 4 1 7    <- the write failed, the first element changed anyway

I like the change.

> Why?
> ====
> Allowing a partial change to a vector after returning from an erroneous
> proc_handler is just plain wrong. This should be handled within sysctl
> to avoid users having to do it for themselves [1]. 
> 
> Behavioral Changes
> ==================
> 1. A failed write will not update the vector
> 2. Vector writes can now fail with -ENOMEM

Yeah, this improves Linux.

> Testing
> =======
> This went through regular sysctl kunit and self test. Also is posted to
> 0-day.
> 
> I always find it difficult to know who wants to receive this. Please let
> me know if you want to be removed from the Cc/To.

Sashiko said one thing:
	https://sashiko.dev/#/patchset/20260814-lklm-partial_ctlvec-v2-0-9df50d26e477@kernel.org