Off-by-one in arch/mips/bcm47xx/time.c (was: [PATCH v6 02/19] string: Add strprefix())

[Alejandro Colomar <alx+linux-hardening@kernel.org>]

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Hi Hauke,

> Date: 2026-11-14 07:53:25-0800
> From: Joe Perches <joe@perches.com>
>
[...]
> And these are all candidates for converted uses to
> whatever is the function name or steq:
> 
> $ git grep -P '[^w]strncmp\s*\(\s*[\w\.\-\>\s]*,\s*\"\w*"\s*,\s*\d+\s*\)' -- '*.[ch]' | wc -l
> 946

Looking at those, I've seen a bug in BCM47XX, introduced in 2224de9d152b
(2013-10-29; "MIPS: BCM47XX: Fix clock detection for BCM5354 with 200MHz
 clock").

Look at this line of code:

	$ grep strncmp arch/mips/bcm47xx/time.c
			if (len >= 0 && !strncmp(buf, "200", 4))

That strncmp(3) call is wrong, as it's really behaving as strcmp(3),
since the 4 is off-by-one.  I'd like to know what was the intention.
Was it meant to be !strncmp(buf, "200", 3)?  Or was it meant to be just
!strcmp(buf, "200")?


Have a lovely night!
Alex

-- 
<https://www.alejandro-colomar.es>

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