Re: [PATCH v4 2/6] string: Warn if the prefix is the empty string

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [High] string: missing linux/bug.h include for WARN_ON_ONCE() in
  str_has_prefix()
--

commit 544547ef558a49b7dbb876a077fff7f7bedc8b0c
Author: Alejandro Colomar <alx@kernel.org>

string: Warn if the prefix is the empty string

This commit adds a WARN_ON_ONCE() check to str_has_prefix() and documents
that passing an empty prefix string is unsupported.

Link: https://lore.kernel.org/linux-hardening/20261104-fwnode-for-each-prop-v1-1-6e28fe1c72c4@oss.qualcomm.com/

> diff --git a/include/linux/string.h b/include/linux/string.h
> index ec6ca50599fed..8e6b78c6196a7 100644
> --- a/include/linux/string.h
> +++ b/include/linux/string.h
> @@ -561,6 +561,10 @@ static inline char *strprefix(const char *s, const char *prefix)
>   * This is similar to strprefix(), but returns an offset instead of
>   * a pointer.
>   *
> + * Unlike for strprefix(), if the prefix is an empty string, the
> + * behavior is undefined.  If you need to support arbitrary prefixes,
> + * use strprefix().
> + *
>   * Returns:
>   * * strlen(@prefix) if @str starts with @prefix
>   * * 0 if @str does not start with @prefix
> @@ -568,6 +572,7 @@ static inline char *strprefix(const char *s, const char *prefix)
>  static __always_inline size_t str_has_prefix(const char *str, const char *prefix)
>  {
>  	size_t len = strlen(prefix);
> +	WARN_ON_ONCE(len == 0);

[Severity: High]
Does include/linux/string.h need to include linux/bug.h for WARN_ON_ONCE()?

Currently, include/linux/string.h only pulls in linux/bug.h transitively
through linux/fortify-string.h when CONFIG_FORTIFY_SOURCE is enabled and
__NO_FORTIFY is not defined. Because str_has_prefix() is an inline function
rather than a macro, translation units that include linux/string.h without
linux/bug.h (such as arch/x86/lib/string_32.c with __NO_FORTIFY, or
lib/net_utils.c when CONFIG_FORTIFY_SOURCE is disabled) fail to build with
an implicit declaration of WARN_ON_ONCE().

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/cover.1794425425.git.alx@kernel.org?part=2