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

[Josh Law <objecting@objecting.org>]

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.

V/R


Josh Law