added --user command

RELNOTES

@@ -6,6 +6,7 @@ firejail (0.9.37) baseline; urgency=low
   * added KMail, Seamonkey, Telegram profiles
   * --join command enhancement (--join-network, --join-filesystem)
   * symlink invocation
+  * --user command
  -- netblue30 <netblue30@yahoo.com>  Tue,  5 Jan 2016 08:00:00 -0500
 
 firejail (0.9.36) baseline; urgency=low

src/firejail/firejail.h

@@ -505,5 +505,8 @@ void fs_logger_print_log(pid_t pid);
 // run_symlink.c
 void run_symlink(int argc, char **argv);
 
+// user.c
+void check_user(int argc, char **argv);
+
 #endif
 

src/firejail/main.c

@@ -514,6 +514,7 @@ int main(int argc, char **argv) {
 	else {
 		// check --output option and execute it;
 		check_output(argc, argv); // the function will not return if --output option was found
+		check_user(argc, argv); // the function will not return if --user option was found
 	}
 	
 	// parse arguments

src/firejail/usage.c

@@ -286,6 +286,7 @@ void usage(void) {
 	printf("\t--tracelog - add a syslog message for every access to files or\n");
 	printf("\t\tdirectoires blacklisted by the security profile.\n\n");
 	printf("\t--tree - print a tree of all sandboxed processes.\n\n");
+	printf("\t--user=new_user - switch the user before starting the sandbox.\n\n");
 	printf("\t--version - print program version and exit.\n\n");
 	printf("\t--whitelist=dirname_or_filename - whitelist directory or file.\n\n");
 	printf("\t--zsh - use /usr/bin/zsh as default shell.\n\n");

src/firejail/user.c

@@ -0,0 +1,114 @@
+/*
+ * Copyright (C) 2014-2016 Firejail Authors
+ *
+ * This file is part of firejail project
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+#include "firejail.h"
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <grp.h>
+#include <pwd.h>
+
+
+void check_user(int argc, char **argv) {
+	int i;
+	char *user = NULL;
+
+	int found = 0;
+	for (i = 1; i < argc; i++) {
+		// check options
+		if (strcmp(argv[i], "--") == 0)
+			break;
+		if (strncmp(argv[i], "--", 2) != 0)
+			break;
+		
+		// check user option		
+		if (strncmp(argv[i], "--user=", 7) == 0) {
+			found = 1;
+			user = argv[i] + 7;
+			break;
+		}
+	}
+	if (!found)
+		return;
+
+	// check root
+	if (getuid() != 0) {
+		fprintf(stderr, "Error: you need to be root to use --user command line option\n");
+		exit(1);
+	}
+	
+	// switch user
+	struct passwd *pw = getpwnam(user);
+	if (!pw) {
+		fprintf(stderr, "Error: cannot find user %s\n", user);
+		exit(1);
+	}
+
+	printf("Switching to user %s, UID %d, GID %d\n", user, pw->pw_uid, pw->pw_gid);
+	int rv = initgroups(user, pw->pw_gid);
+	if (rv == -1) {
+		perror("initgroups");
+		fprintf(stderr, "Error: cannot switch to user %s\n", user);
+	}
+
+	rv = setgid(pw->pw_gid);
+	if (rv == -1) {
+		perror("setgid");
+		fprintf(stderr, "Error: cannot switch to user %s\n", user);
+	}
+
+	rv = setuid(pw->pw_uid);
+	if (rv == -1) {
+		perror("setuid");
+		fprintf(stderr, "Error: cannot switch to user %s\n", user);
+	}
+
+	// build the new command line
+	int len = 0;
+	for (i = 0; i < argc; i++) {
+		len += strlen(argv[i]) + 1; // + ' '
+	}
+	
+	char *cmd = malloc(len + 1); // + '\0'
+	if (!cmd)
+		errExit("malloc");
+	
+	char *ptr = cmd;
+	int first = 1;
+	for (i = 0; i < argc; i++) {
+		if (strncmp(argv[i], "--user=", 7) == 0 && first) {
+			first = 0;
+			continue;
+		}
+		
+		ptr += sprintf(ptr, "%s ", argv[i]);
+	}
+
+	// run command
+	char *a[4];
+	a[0] = "/bin/bash";
+	a[1] = "-c";
+	a[2] = cmd;
+	a[3] = NULL;
+
+	execvp(a[0], a); 
+
+	perror("execvp");
+	exit(1);
+}

src/man/firejail.txt

@@ -1441,6 +1441,15 @@ $ firejail \-\-tree
 .br
   11970:netblue:transmission-gtk 
 .TP
+\fB\-\-user=new-user
+Switch the user before starting the sandbox. This command should be run as root.
+.br
+
+.br
+Example:
+.br
+# firejail \-\-user=www-data
+.TP
 \fB\-\-version
 Print program version and exit.
 .br