Re: [PATCH] refs.c: add a function to append a reflog entry to a fd

From: Junio C Hamano <gitster@pobox.com>
Date: Nov 20, 2014, 01:34 UTC
Message-ID: <xmqqvbma4pu3.fsf@gitster.dls.corp.google.com>
In-Reply-To: <xmqqzjbm4qe5.fsf@gitster.dls.corp.google.com>

Junio C Hamano <gitster@pobox.com> writes:

Show 12 quoted lines

> Stefan Beller <sbeller@google.com> writes:
>
>> Compared to the last send of this patch[1], there was one change in the print
>> function. Replaced sprintf by snprintf for security reasons. 
>
> Careful.  I despise people who blindly think strlcpy() and
> snprintf() are good solutions for for security.  They are by
> themselves not.
> ...
> So use of snprintf() is not really buying you much here, not in the
> current code certainly, but not as a future-proofing measure,
> either.

Don't get me wrong. I am not saying that using snprintf() here is bad per-se. There should be no difference.

But I do not want to see people getting in the habit of thinking "I now use snprintf/strlcpy instead of sprintf/strcpy, and made my code more secure." Often they are not doing that.

The only case snprintf/strlcpy is useful is when your data does not matter in its detail. E.g. when you are preparing human-readble data whose first part is sufficient to convey the information you want to convey, you would be perfectly happy if the result is truncated. In such a case, counting to allocate enough to hold everything and running sprintf() only to chop the result later is not necessary --- it still is not wrong, though --- and allocating enough to satisify the eventual chop length and using snprintf() is easier way to achieve the same result.

But I do not think this codepath falls into such an "I am willing to lose data" case.