Re: [PATCH] diff: avoid stack-buffer-read-overrun for very long name

From: Jim Meyering <jim@meyering.net>
Date: Apr 26, 2012, 16:22 UTC
Message-ID: <874ns6xy30.fsf@rho.meyering.net>
In-Reply-To: <xmqq62cma2uo.fsf@junio.mtv.corp.google.com>

Junio C Hamano wrote:

Show 19 quoted lines

> Jim Meyering <jim@meyering.net> writes:
>
>> What do you think about replacing those two append-if-needed two-liners:
>>
>>     if (buffer2.len && buffer2.buf[buffer2.len - 1] != '/')
>>             strbuf_addch(&buffer2, '/');
>>
>> by something that readably encapsulates the idiom:
>>
>>     strbuf_append_if_absent (&buffer2, '/');
>>
>> (though the name isn't particularly apt, because you might
>> take "absent" to mean "not anywhere in the string," so maybe
>>   strbuf_append_if_not_already_at_end (ugly) or
>>   strbuf_append_uniq
>> )
>
> I am not good at names, but strbuf_terminate_with(&buffer2, '/')
> perhaps?

Maybe, but it still doesn't evoke the conditional nature of don't-append-if-already-there the operation. i.e., one might wonder how it's different from "strbuf_append".

How about one of these?

  strbuf_ensure_suffix  // but might make you think suffix==more than 1 byte
  strbuf_ensure_last_byte    // maybe?
  strbuf_ensure_last_byte_is // rather long, but apt

Show 11 quoted lines

>> There are several other uses that would benefit from such a transformation:
>> To find the easy ones, I ran this:
>>
>>   git grep -B1 "strbuf_addch.*'"|grep -A1 '!='
>>
>> I've manually marked/separated the ones that don't apply.
>>
>> Note how only 2 of the 6 candidates ensure that length is positive
>> before using ".len - 1":
>
> Yikes, that is embarrasing ;-)

Knowing you/git, each is because the buffer is known to be non-empty.