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

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(-)
>