Re: [PATCH 0/3] module: Add compile-time check for embedded NUL characters

Hans Verkuil
2025-10-08T06:27:29Z

On 08/10/2025 05:59, Kees Cook wrote:
> Hi,
>
> A long time ago we had an issue with embedded NUL bytes in MODULE_INFO
> strings[1]. While this stands out pretty strongly when you look at the
> code, and we can't do anything about a binary module that just plain lies,
> we never actually implemented the trivial compile-time check needed to
> detect it.
>
> Add this check (and fix 2 instances of needless trailing semicolons that
> this change exposed).
>
> Note that these patches were produced as part of another LLM exercise.
> This time I wanted to try "what happens if I ask an LLM to go read
> a specific LWN article and write a patch based on a discussion?" It
> pretty effortlessly chose and implemented a suggested solution, tested
> the change, and fixed new build warnings in the process.
>
> Since this was a relatively short session, here's an overview of the
> prompts involved as I guided it through a clean change and tried to see
> how it would reason about static_assert vs _Static_assert. (It wanted
> to use what was most common, not what was the current style -- we may
> want to update the comment above the static_assert macro to suggest
> using _Static_assert directly these days...)
>
> I want to fix a weakness in the module info strings. Read about it
> here: https://lwn.net/Articles/82305/
>
> Since it's only "info" that we need to check, can you reduce the checks
> to just that instead of all the other stuff?
>
> I think the change to the comment is redundent, and that should be
> in a commit log instead. Let's just keep the change to the static assert.
>
> Is "static_assert" the idiomatic way to use a static assert in this
> code base? I've seen _Static_assert used sometimes.
>
> What's the difference between the two?
>
> Does Linux use C11 by default now?
>
> Then let's not use the wrapper any more.
>
> Do an "allmodconfig all -s" build to verify this works for all modules
> in the kernel.
>
>
> Thanks!
>
> -Kees
>
> [1] https://lwn.net/Articles/82305/
>
> Kees Cook (3):
> media: dvb-usb-v2: lmedm04: Fix firmware macro definitions
> media: radio: si470x: Fix DRIVER_AUTHOR macro definition
> module: Add compile-time check for embedded NUL characters

I reviewed the two media patches. Feel free to take this series.
If you prefer that I take the two media patches, then let me know
but it makes more sense in this case that you take all three.

Regards,

Hans

>
> include/linux/moduleparam.h | 3 +++
> drivers/media/radio/si470x/radio-si470x-i2c.c | 2 +-
> drivers/media/usb/dvb-usb-v2/lmedm04.c | 12 ++++++------
> 3 files changed, 10 insertions(+), 7 deletions(-)
>