module: Add compile-time check for embedded NUL characters

v2:
- use static_assert instead of _Static_assert
- add Hans's Reviewed-by's
v1: https://lore.kernel.org/lkml/[email protected]/

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(-)

2.34.1