Re: [PATCH v3 04/10] daemon: recognize hidden request arguments

On Tue,  3 Oct 2017 13:15:01 -0700
Brandon Williams [off-list ref] wrote:

 /*
  * Read the host as supplied by the client connection.

The return value is probably worth documenting. Something like "Returns
a pointer to the character *after* the NUL byte terminating the host
argument, or extra_args if there is no host argument."

  */
-static void parse_host_arg(struct hostinfo *hi, char *extra_args, int buflen)
+static char *parse_host_arg(struct hostinfo *hi, char *extra_args, int buflen)

[snip]

+static void parse_extra_args(struct hostinfo *hi, struct argv_array *env,
+			     char *extra_args, int buflen)
+{
+	const char *end = extra_args + buflen;
+	struct strbuf git_protocol = STRBUF_INIT;
+
+	/* First look for the host argument */
+	extra_args = parse_host_arg(hi, extra_args, buflen);

This works, but is a bit loose in what it accepts. I think it's better
to be tighter - in particular, if there is no host argument, we
shouldn't be looking for extra args.

+
+	/* Look for additional arguments places after a second NUL byte */
+	for (; extra_args < end; extra_args += strlen(extra_args) + 1) {

Assuming that the host argument exists, this for loop should start at
extra_args + 1 to skip the second NUL byte. This currently works
because this code is lenient towards empty strings.

+		const char *arg = extra_args;
+
+		/*
+		 * Parse the extra arguments, adding most to 'git_protocol'
+		 * which will be used to set the 'GIT_PROTOCOL' envvar in the
+		 * service that will be run.
+		 *
+		 * If there ends up being a particular arg in the future that
+		 * git-daemon needs to parse specificly (like the 'host' arg)
+		 * then it can be parsed here and not added to 'git_protocol'.
+		 */
+		if (*arg) {
+			if (git_protocol.len > 0)
+				strbuf_addch(&git_protocol, ':');
+			strbuf_addstr(&git_protocol, arg);
+		}
+	}

But I think we shouldn't be lenient towards empty strings.

+
+	if (git_protocol.len > 0)
+		argv_array_pushf(env, GIT_PROTOCOL_ENVIRONMENT "=%s",
+				 git_protocol.buf);
+	strbuf_release(&git_protocol);
 }