Re: [PATCH] lib/string: replace BUG_ON with WARN_ON_ONCE in strlcat

[Josh Law <objecting@objecting.org>]

On 16 March 2026 16:43:12 GMT, Andy Shevchenko <andriy.shevchenko@intel.com> wrote:
>On Mon, Mar 16, 2026 at 04:36:40PM +0000, Josh Law wrote:
>> On 16 March 2026 16:30:15 GMT, Andy Shevchenko <andriy.shevchenko@intel.com> wrote:
>> >On Mon, Mar 16, 2026 at 04:17:28PM +0000, Josh Law wrote:
>> >> BUG_ON() in a library function is too harsh -- it panics the kernel
>> >> when a caller passes a dest string whose length already meets or
>> >> exceeds count. This is a caller bug, not a reason to bring down the
>> >> entire system.
>> >> 
>> >> Replace with WARN_ON_ONCE() and a safe early return. The return value
>> >> of count signals truncation to the caller, consistent with strlcat
>> >> semantics (return >= count means the output was truncated).
>> >> 
>> >> This follows the guidance in include/asm-generic/bug.h which
>> >> explicitly discourages BUG_ON: "Don't use BUG() or BUG_ON() unless
>> >> there's really no way out."
>> >
>> >First of all, this doesn't really change much, especially if one uses
>> >panic_on_oops.
>> >
>> >Second, the entire function is kinda deprecated, it's better just to drop it.
>> >
>> >$ git grep -lw strlcat | wc -l
>> >142
>> >
>> >(In reality it's less as tools and implementation are not users of it)
>> >
>> >Third, if the caller is that problematic this may lead to the serious
>> >(security) issues.
>> >
>> >Based on that, NAK.
>> 
>> Hmm, good call, but how would I implement that? BUG_ON seems a bit too harsh
>> for a library function.
>
>Drop the function. Start from converting users to strscpy() or similar
>(we have a few for different cases) and then drop strlcat() all for good.
>


Okie dokie. I'm doing a patch on that right now, keep your eyes peeled on your emails, thanks for the suggestion 


V/R


Josh Law