Subject: Re: [PATCH] Docs: web server must setenv GIT_PROTOCOL for v2

From: Junio C Hamano <[email-masked]>
Date: Thu, 09 Sep 2021 10:28:50 -0700

Jeff King <[email-masked]> writes:

> On Wed, Sep 08, 2021 at 06:48:47AM -0400, Jeff King wrote:
>
>> Both of the included examples here have been tested to work. The one for
>> lighttpd is a little less direct than I'd like, but I couldn't find a
>> way to directly set an environment variable to the value of a request
>> header. From my reading of the documentation, lighttpd will set
>> HTTP_GIT_PROTOCOL automatically, but git-http-backend looks only at
>> GIT_PROTOCOL. Arguably http-backend should do this translation itself.

Nice.

These headers get HTTP_* prefixed as a security measure when servers
expose them to their configuration mechanisms because these names
are attacker controlled.  I had a flawed mental model in which the
servers' configuration controls which one of these resulting HTTP_*
headers are passed to CGI and externals selectively, but if servers
pass all HTTP_* environment variables to CGI and externals without
any filtering, the patch you gave here is the most logical solution.

Will queue.

> -- >8 --
> Subject: [PATCH] http-backend: handle HTTP_GIT_PROTOCOL CGI variable
>
> When a client requests the v2 protocol over HTTP, they set the
> Git-Protocol header. Webservers will generaly make that available to our
> CGI as HTTP_GIT_PROTOCOL in the environment. However, that's not
> sufficient for upload-pack, etc, to respect it; they look in
> GIT_PROTOCOL (without the HTTP_ prefix).
>
> Either the webserver or the CGI is responsible for relaying that HTTP
> header into the GIT_PROTOCOL variable. Traditionally, our tests have
> configured the webserver to do so, but that's a burden on the server
> admin. We can make this work out of the box by having the http-backend
> CGI copy the contents.
>
> Signed-off-by: Jeff King <[email-masked]>
> ---
>  http-backend.c          | 4 ++++
>  t/lib-httpd/apache.conf | 2 --
>  2 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/http-backend.c b/http-backend.c
> index b329bf63f0..2f4b4c11de 100644
> --- a/http-backend.c
> +++ b/http-backend.c
> @@ -739,6 +739,7 @@ static int bad_request(struct strbuf *hdr, const struct service_cmd *c)
>  int cmd_main(int argc, const char **argv)
>  {
>  	char *method = getenv("REQUEST_METHOD");
> +	const char *proto_header;
>  	char *dir;
>  	struct service_cmd *cmd = NULL;
>  	char *cmd_arg = NULL;
> @@ -789,6 +790,9 @@ int cmd_main(int argc, const char **argv)
>  	http_config();
>  	max_request_buffer = git_env_ulong("GIT_HTTP_MAX_REQUEST_BUFFER",
>  					   max_request_buffer);
> +	proto_header = getenv("HTTP_GIT_PROTOCOL");
> +	if (proto_header)
> +		setenv(GIT_PROTOCOL_ENVIRONMENT, proto_header, 1);
>  
>  	cmd->imp(&hdr, cmd_arg);
>  	return 0;
> diff --git a/t/lib-httpd/apache.conf b/t/lib-httpd/apache.conf
> index afa91e38b0..71761e3299 100644
> --- a/t/lib-httpd/apache.conf
> +++ b/t/lib-httpd/apache.conf
> @@ -81,8 +81,6 @@ PassEnv GIT_TRACE
>  PassEnv GIT_CONFIG_NOSYSTEM
>  PassEnv GIT_TEST_SIDEBAND_ALL
>  
> -SetEnvIf Git-Protocol ".*" GIT_PROTOCOL=$0
> -
>  Alias /dumb/ www/
>  Alias /auth/dumb/ www/auth/dumb/