Hi,
I put together a first patch for the issue.

Mit freundlichen Grüßen / With kind regards
Florian Manschwetus

E-Mail: manschwetus@cs-software-gmbh.de
Tel.: +49-(0)611-8908534
 
CS Software Concepts and Solutions GmbH
Geschäftsführer / Managing director: Dr. Werner Alexi 
Amtsgericht Wiesbaden HRB 10004 (Commercial registry)
Schiersteiner Straße 31
D-65187 Wiesbaden
Germany
Tel.: 0611/8908555


-----Ursprüngliche Nachricht-----
Von: Konstantin Khomoutov [mailto:kostix+git@007spb.ru] 
Gesendet: Donnerstag, 10. März 2016 13:55
An: Florian Manschwetus
Cc: git@vger.kernel.org
Betreff: Re: Problem with git-http-backend.exe as iis cgi

On Thu, 10 Mar 2016 07:28:50 +0000
Florian Manschwetus <manschwetus@cs-software-gmbh.de> wrote:

> I tried to setup git-http-backend with iis, as iis provides proper 
> impersonation for cgi under windows, which leads to have the 
> filesystem access performed with the logon user, therefore the 
> webserver doesn't need generic access to the files. I stumbled across 
> a problem, ending up with post requests hanging forever. After some 
> investigation I managed to get it work by wrapping the http-backend 
> into a bash script, giving a lot of control about the environmental 
> things, I was unable to solve within IIS configuration. The 
> workaround, I use currently, is to use "/bin/head -c ${CONTENT_LENGTH} 
> | ./git-http-backend.exe", which directly shows the issue. Git 
> http-backend should check if CONTENT_LENGTH is set to something 
> reasonable (e.g. >0) and should in this case read only CONTENT_LENGTH 
> bytes from stdin, instead of reading till EOF what I suspect it is 
> doing currently.

The rfc [1] states in its section 4.2:

| A request-body is supplied with the request if the CONTENT_LENGTH is 
| not NULL.  The server MUST make at least that many bytes available for 
| the script to read.  The server MAY signal an end-of-file condition 
| after CONTENT_LENGTH bytes have been read or it MAY supply extension 
| data.  Therefore, the script MUST NOT attempt to read more than 
| CONTENT_LENGTH bytes, even if more data is available.  However, it is 
| not obliged to read any of the data.

So yes, if Git currently reads until EOF, it's an error.
The correct way would be:

1) Check to see if the CONTENT_LENGTH variable is available in the
   environment.  If no, read nothing.

2) Otherwise read as many bytes it specifies, and no more.

1. https://www.ietf.org/rfc/rfc3875