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

From: Junio C Hamano <gitster@pobox.com>
Date: Jul 5, 2023, 22:27 UTC
Message-ID: <xmqqsfa2uh83.fsf@gitster.g>
In-Reply-To: <6f984150-5a98-b2b8-1791-b101f5953b7a@web.de>

René Scharfe <l.s.r@web.de> writes:

> Sure, that's done.  If any of the four characters is not a hexadecimal
> digit then packet_length() returns a negative value, before and after
> the change.

Ah, it is the beauty of hexval[] table ;-)

So as long as we are sure that we are not running beyond the end of the buffer, we are OK. And as I already said, I think "this change is safe for our two callers; those adding more callers in the future are better be very careful" is probably good enough for this one.

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.