connect: reject paths that look like command line options

If we get a repo path like "-repo.git", we may try to invoke
"git-upload-pack -repo.git". This is going to fail, since
upload-pack will interpret it as a set of bogus options. But
let's reject this before we even run the sub-program, since
we would not want to allow any mischief with repo names that
actually are real command-line options.

You can still ask for such a path via git-daemon, but there's no
security problem there, because git-daemon enters the repo itself
and then passes "."  on the command line.

Signed-off-by: Jeff King <peff@peff.net>
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

connect.c

@@ -727,6 +727,9 @@ struct child_process *git_connect(int fd[2], const char *url,
 		conn = xmalloc(sizeof(*conn));
 		child_process_init(conn);
 
+		if (looks_like_command_line_option(path))
+			die("strange pathname '%s' blocked", path);
+
 		strbuf_addstr(&cmd, prog);
 		strbuf_addch(&cmd, ' ');
 		sq_quote_buf(&cmd, path);