Allow creation of arbitrary git-shell commands

[thirdparty/git.git] / shell.c

#include "cache.h"
#include "quote.h"
#include "exec_cmd.h"
#include "strbuf.h"

#define COMMAND_DIR "git-shell-commands"

static int do_generic_cmd(const char *me, char *arg)
{
	const char *my_argv[4];

	setup_path();
	if (!arg || !(arg = sq_dequote(arg)))
		die("bad argument");
	if (prefixcmp(me, "git-"))
		die("bad command");

	my_argv[0] = me + 4;
	my_argv[1] = arg;
	my_argv[2] = NULL;

	return execv_git_cmd(my_argv);
}

static int do_cvs_cmd(const char *me, char *arg)
{
	const char *cvsserver_argv[3] = {
		"cvsserver", "server", NULL
	};

	if (!arg || strcmp(arg, "server"))
		die("git-cvsserver only handles server: %s", arg);

	setup_path();
	return execv_git_cmd(cvsserver_argv);
}

static int is_valid_cmd_name(const char *cmd)
{
	/* Test command contains no . or / characters */
	return cmd[strcspn(cmd, "./")] == '\0';
}

static char *make_cmd(const char *prog)
{
	char *prefix = xmalloc((strlen(prog) + strlen(COMMAND_DIR) + 2));
	strcpy(prefix, COMMAND_DIR);
	strcat(prefix, "/");
	strcat(prefix, prog);
	return prefix;
}

static void cd_to_homedir(void)
{
	const char *home = getenv("HOME");
	if (!home)
		die("could not determine user's home directory; HOME is unset");
	if (chdir(home) == -1)
		die("could not chdir to user's home directory");
}

static struct commands {
	const char *name;
	int (*exec)(const char *me, char *arg);
} cmd_list[] = {
	{ "git-receive-pack", do_generic_cmd },
	{ "git-upload-pack", do_generic_cmd },
	{ "git-upload-archive", do_generic_cmd },
	{ "cvs", do_cvs_cmd },
	{ NULL },
};

int main(int argc, char **argv)
{
	char *prog;
	const char **user_argv;
	struct commands *cmd;
	int devnull_fd;

	/*
	 * Always open file descriptors 0/1/2 to avoid clobbering files
	 * in die().  It also avoids not messing up when the pipes are
	 * dup'ed onto stdin/stdout/stderr in the child processes we spawn.
	 */
	devnull_fd = open("/dev/null", O_RDWR);
	while (devnull_fd >= 0 && devnull_fd <= 2)
		devnull_fd = dup(devnull_fd);
	if (devnull_fd == -1)
		die_errno("opening /dev/null failed");
	close (devnull_fd);

	/*
	 * Special hack to pretend to be a CVS server
	 */
	if (argc == 2 && !strcmp(argv[1], "cvs server"))
		argv--;

	/*
	 * We do not accept anything but "-c" followed by "cmd arg",
	 * where "cmd" is a very limited subset of git commands.
	 */
	else if (argc != 3 || strcmp(argv[1], "-c"))
		die("What do you think I am? A shell?");

	prog = xstrdup(argv[2]);
	if (!strncmp(prog, "git", 3) && isspace(prog[3]))
		/* Accept "git foo" as if the caller said "git-foo". */
		prog[3] = '-';

	for (cmd = cmd_list ; cmd->name ; cmd++) {
		int len = strlen(cmd->name);
		char *arg;
		if (strncmp(cmd->name, prog, len))
			continue;
		arg = NULL;
		switch (prog[len]) {
		case '\0':
			arg = NULL;
			break;
		case ' ':
			arg = prog + len + 1;
			break;
		default:
			continue;
		}
		exit(cmd->exec(cmd->name, arg));
	}

	cd_to_homedir();
	if (split_cmdline(prog, &user_argv) != -1) {
		if (is_valid_cmd_name(user_argv[0])) {
			prog = make_cmd(user_argv[0]);
			user_argv[0] = prog;
			execv(user_argv[0], (char *const *) user_argv);
		}
		free(prog);
		free(user_argv);
		die("unrecognized command '%s'", argv[2]);
	} else {
		free(prog);
		die("invalid command format '%s'", argv[2]);
	}
}