core-agent-linux/qubes-rpc/qfile-unpacker.c

#define _GNU_SOURCE
#include <grp.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <pwd.h>
#include <sys/stat.h>
#include <sys/mount.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>
#include <sys/fsuid.h>
#include <gui-fatal.h>
#include <errno.h>
#include <libqubes-rpc-filecopy.h>
#define INCOMING_DIR_ROOT "/home/user/QubesIncoming"
int prepare_creds_return_uid(const char *username)
{
	const struct passwd *pwd;
	pwd = getpwnam(username);
	if (!pwd) {
		perror("getpwnam");
		exit(1);
	}
	setenv("HOME", pwd->pw_dir, 1);
	setenv("USER", username, 1);
	if (setgid(pwd->pw_gid) < 0)
		gui_fatal("Error setting group permissions");
	if (initgroups(username, pwd->pw_gid) < 0)
		gui_fatal("Error initializing groups");
	if (setfsuid(pwd->pw_uid) < 0)
		gui_fatal("Error setting filesystem level permissions");
	return pwd->pw_uid;
}

int main(int argc __attribute((__unused__)), char ** argv __attribute__((__unused__)))
{
	char *incoming_dir;
	int uid, ret;
	pid_t pid;
	const char *remote_domain;
	char *procdir_path;
	int procfs_fd;

	uid = prepare_creds_return_uid("user");

	remote_domain = getenv("QREXEC_REMOTE_DOMAIN");
	if (!remote_domain) {
		gui_fatal("Cannot get remote domain name");
		exit(1);
	}
	mkdir(INCOMING_DIR_ROOT, 0700);
	if (asprintf(&incoming_dir, "%s/%s", INCOMING_DIR_ROOT, remote_domain) < 0)
		gui_fatal("Error allocating memory"); 
	mkdir(incoming_dir, 0700);
	if (chdir(incoming_dir))
		gui_fatal("Error chdir to %s", incoming_dir); 

	if (mount(".", ".", NULL, MS_BIND | MS_NODEV | MS_NOEXEC | MS_NOSUID, NULL) < 0)
		gui_fatal("Failed to mount a directory %s", incoming_dir);

	/* parse the input in unprivileged child process, parent will hold root
	 * access to unmount incoming dir */
	switch (pid=fork()) {
		case -1:
			gui_fatal("Failed to create new process");
		case 0:
			if (asprintf(&procdir_path, "/proc/%d/fd", getpid()) < 0) {
				gui_fatal("Error allocating memory");
			}
			procfs_fd = open(procdir_path, O_DIRECTORY | O_RDONLY);
			if (procfs_fd < 0)
				perror("Failed to open /proc");
			else
				set_procfs_fd(procfs_fd);
			free(procdir_path);

			if (chroot("."))
				gui_fatal("Error chroot to %s", incoming_dir);
			if (setuid(uid) < 0) {
				/* no kdialog inside chroot */
				perror("setuid");
				exit(1);
			}
			return do_unpack();
	}
	if (waitpid(pid, &ret, 0) < 0) {
		gui_fatal("Failed to wait for child process");
	}
	if (umount2(".", MNT_DETACH) < 0)
		gui_fatal("Cannot umount incoming directory");
	return ret;
}