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

Kees Cook
2025-10-08T03:59:38Z

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

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(-)

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2.34.1