Re: [PATCH] apply: use strcmp(3) for comparing strings in gitdiff_verify_name()

From: René Scharfe <l.s.r@web.de>
Date: Jul 9, 2017, 12:20 UTC
Message-ID: <df3bd047-6ddd-c120-54dd-4165d2257bb0@web.de>
In-Reply-To: <87o9svgia8.fsf@linux-m68k.org>

Am 08.07.2017 um 15:38 schrieb Andreas Schwab:

Show 15 quoted lines

> On Jul 08 2017, René Scharfe <l.s.r@web.de> wrote:
> 
>> Am 08.07.2017 um 13:08 schrieb Andreas Schwab:
>>> On Jul 08 2017, René Scharfe <l.s.r@web.de> wrote:
>>>
>>>> Avoid running over the end of another -- a C string whose length we
>>>> don't know -- by using strcmp(3) instead of memcmp(3) for comparing it
>>>> with another C string.
>>>
>>> That's not a good justification for the change, since memcmp never reads
>>> past the differing characters.
>>
>> Interesting.  Where does that guarantee come from?
> 
> Sorry, I misremembered.  It's only memchr that has this restriction.

Hmm, I can't get ASan to complain about memchr reading beyond the end of a C string, but I don't know why. Glibc reads full words [1], and I don't see how the standard [2] forbids reading past the found byte.

René

[1] https://sourceware.org/git/?p=glibc.git;a=blob;f=string/memchr.c [2] http://pubs.opengroup.org/onlinepubs/009695399/functions/memchr.html