Re: git error in tag ...: unterminated header

From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Jun 25, 2015, 21:07 UTC
Message-ID: <2b124e09d9c89ff3892f246ea91aa3c4@www.dscho.org>
In-Reply-To: <xmqqegkzy1ri.fsf@gitster.dls.corp.google.com>

Hi Junio & Wolfgang,

On 2015-06-25 22:24, Junio C Hamano wrote:

Show 7 quoted lines

> Wolfgang Denk <wd@denx.de> writes:
> 
>> In message <xmqqegkzzoaz.fsf@gitster.dls.corp.google.com> you wrote:
>>>
>>> > Question is: how can we fix that?
>>>
>>> It could be that 4d0d8975 is buggy and barking at a non breakage.

Well, I would like to believe that this commit made our code *safer* by making sure that we would never overrun the buffer. Remember: under certain circumstances, the buffer passed to the fsck machinery is *not* terminated by a NUL. The code I introduced simply verifies that there is an empty line because the fsck code stops there and does not look further.

If the buffer does *not* contain an empty line, the fsck code runs the danger of looking beyond the allocated memory because it uses functions that assume NUL-terminated strings, while the buffer passed to the fsck code is a counted string.

The quick & dirty work-around would be to detect when the buffer does not contain an empty line and to make a NUL-terminated copy in that case.

A better solution was outlined by Peff back when I submitted those patches: change all the code paths that read objects and make sure that all of them are terminated by a NUL. AFAIR some code paths did that already, but not all of them.

Ciao, Dscho