Re: [PATCH] pkt-line: don't check string length in packet_length()

From: René Scharfe <l.s.r@web.de>
Date: Jul 6, 2023, 05:07 UTC
Message-ID: <a5acfab5-0133-b3d6-3efc-c3f107e78b58@web.de>
In-Reply-To: <xmqqsfa2uh83.fsf@gitster.g>

Am 06.07.23 um 00:27 schrieb Junio C Hamano:

Show 7 quoted lines

> hex.h:hex2chr() says "don't run over the end of short strings", but
> as far as I can see it does not check any such thing; find a page of
> memory, whose next page is unmapped, and pointing *s at the last
> byte of that page and calling it will happily run over the end and
> would cause SIGBUS.  The function assumes that such a short string
> is always NUL terminated, which is not a great way to guarantee that
> we do not run over the end of strings.

Yes, hex2chr() works with C strings, i.e. those that end with a NUL character. An empty string is just a NUL byte, a string of length 1 is a non-NUL byte and a NUL. The function reads one byte from the former and otherwise two bytes -- no overrun.

If a C string loses its NUL, how could you detect its end?

René