Subject: Re: [PATCH] daemon: --access-hook option

From: Michal Novotny <[email-masked]>
Date: Tue, 21 Aug 2012 12:57:35 +0200

Right, this approach of having ACL using the --access-hook option looks
much better. At least you got inspired this could be useful for somebody ;-)

Michal

On 08/15/2012 07:12 AM, Junio C Hamano wrote:
> The --access-hook option to "git daemon" specifies an external
> command to be run every time a client connects, with
>
>  - service name (e.g. "upload-pack", etc.),
>  - path to the repository,
>  - hostname (%H),
>  - canonical hostname (%CH),
>  - ip address (%IP),
>  - tcp port (%P)
>
> as its command line arguments.  The external command can decide to
> decline the service by exiting with a non-zero status (or to allow it
> by exiting with a zero status).  It can also look at the $REMOTE_ADDR
> and $REMOTE_PORT environment variables to learn about the requestor
> when making this decision.
>
> The external command can optionally write a single line to its
> standard output to be sent to the requestor as an error message when
> it declines the service.
>
> Signed-off-by: Junio C Hamano <[email-masked]>
> ---
>
>  * This time, minimally tested, with a documentation update.
>
>  Documentation/git-daemon.txt | 16 +++++++++
>  daemon.c                     | 77 ++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 93 insertions(+)
>
> diff --git a/Documentation/git-daemon.txt b/Documentation/git-daemon.txt
> index 31b28fc..c3ba4d7 100644
> --- a/Documentation/git-daemon.txt
> +++ b/Documentation/git-daemon.txt
> @@ -16,6 +16,7 @@ SYNOPSIS
>  	     [--reuseaddr] [--detach] [--pid-file=<file>]
>  	     [--enable=<service>] [--disable=<service>]
>  	     [--allow-override=<service>] [--forbid-override=<service>]
> +	     [--access-hook=<path>]
>  	     [--inetd | [--listen=<host_or_ipaddr>] [--port=<n>] [--user=<user> [--group=<group>]]
>  	     [<directory>...]
>  
> @@ -171,6 +172,21 @@ the facility of inet daemon to achieve the same before spawning
>  	errors are not enabled, all errors report "access denied" to the
>  	client. The default is --no-informative-errors.
>  
> +--access-hook=<path>::
> +	Every time a client connects, first run an external command
> +	specified by the <path> with service name (e.g. "upload-pack"),
> +	path to the repository, hostname (%H), canonical hostname
> +	(%CH), ip address (%IP), and tcp port (%P) as its command line
> +	arguments. The external command can decide to decline the
> +	service by exiting with a non-zero status (or to allow it by
> +	exiting with a zero status).  It can also look at the $REMOTE_ADDR
> +	and $REMOTE_PORT environment variables to learn about the
> +	requestor when making this decision.
> ++
> +The external command can optionally write a single line to its
> +standard output to be sent to the requestor as an error message when
> +it declines the service.
> +
>  <directory>::
>  	A directory to add to the whitelist of allowed directories. Unless
>  	--strict-paths is specified this will also include subdirectories
> diff --git a/daemon.c b/daemon.c
> index ab21e66..4602b46 100644
> --- a/daemon.c
> +++ b/daemon.c
> @@ -30,6 +30,7 @@ static const char daemon_usage[] =
>  "           [--interpolated-path=<path>]\n"
>  "           [--reuseaddr] [--pid-file=<file>]\n"
>  "           [--(enable|disable|allow-override|forbid-override)=<service>]\n"
> +"           [--access-hook=<path>]\n"
>  "           [--inetd | [--listen=<host_or_ipaddr>] [--port=<n>]\n"
>  "                      [--detach] [--user=<user> [--group=<group>]]\n"
>  "           [<directory>...]";
> @@ -256,6 +257,71 @@ static int daemon_error(const char *dir, const char *msg)
>  	return -1;
>  }
>  
> +static char *access_hook;
> +
> +static int run_access_hook(struct daemon_service *service, const char *dir, const char *path)
> +{
> +	struct child_process child;
> +	struct strbuf buf = STRBUF_INIT;
> +	const char *argv[8];
> +	const char **arg = argv;
> +	char *eol;
> +	int seen_errors = 0;
> +
> +#define STRARG(x) ((x) ? (x) : "")
> +	*arg++ = access_hook;
> +	*arg++ = service->name;
> +	*arg++ = path;
> +	*arg++ = STRARG(hostname);
> +	*arg++ = STRARG(canon_hostname);
> +	*arg++ = STRARG(ip_address);
> +	*arg++ = STRARG(tcp_port);
> +	*arg = NULL;
> +#undef STRARG
> +
> +	memset(&child, 0, sizeof(child));
> +	child.use_shell = 1;
> +	child.argv = argv;
> +	child.no_stdin = 1;
> +	child.no_stderr = 1;
> +	child.out = -1;
> +	if (start_command(&child)) {
> +		logerror("daemon access hook '%s' failed to start",
> +			 access_hook);
> +		goto error_return;
> +	}
> +	if (strbuf_read(&buf, child.out, 0) < 0) {
> +		logerror("failed to read from pipe to daemon access hook '%s'",
> +			 access_hook);
> +		strbuf_reset(&buf);
> +		seen_errors = 1;
> +	}
> +	if (close(child.out) < 0) {
> +		logerror("failed to close pipe to daemon access hook '%s'",
> +			 access_hook);
> +		seen_errors = 1;
> +	}
> +	if (finish_command(&child))
> +		seen_errors = 1;
> +
> +	if (!seen_errors) {
> +		strbuf_release(&buf);
> +		return 0;
> +	}
> +
> +error_return:
> +	strbuf_ltrim(&buf);
> +	if (!buf.len)
> +		strbuf_addstr(&buf, "service rejected");
> +	eol = strchr(buf.buf, '\n');
> +	if (eol)
> +		*eol = '\0';
> +	errno = EACCES;
> +	daemon_error(dir, buf.buf);
> +	strbuf_release(&buf);
> +	return -1;
> +}
> +
>  static int run_service(char *dir, struct daemon_service *service)
>  {
>  	const char *path;
> @@ -304,6 +370,13 @@ static int run_service(char *dir, struct daemon_service *service)
>  	}
>  
>  	/*
> +	 * Optionally, a hook can choose to deny access to the
> +	 * repository depending on the phase of the moon.
> +	 */
> +	if (access_hook && run_access_hook(service, dir, path))
> +		return -1;
> +
> +	/*
>  	 * We'll ignore SIGTERM from now on, we have a
>  	 * good client.
>  	 */
> @@ -1142,6 +1215,10 @@ int main(int argc, char **argv)
>  			export_all_trees = 1;
>  			continue;
>  		}
> +		if (!prefixcmp(arg, "--access-hook=")) {
> +			access_hook = arg + 14;
> +			continue;
> +		}
>  		if (!prefixcmp(arg, "--timeout=")) {
>  			timeout = atoi(arg+10);
>  			continue;

-- 
Michal Novotny <[email-masked]>, RHCE, Red Hat
Virtualization | libvirt-php bindings | php-virt-control.org