added --user command

5 files changed, 128 insertions, 0 deletions

diff --git a/src/firejail/firejail.h b/src/firejail/firejail.h
index 21ca6c508..a2afd4a8d 100644
--- a/src/firejail/firejail.h
+++ b/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
 
diff --git a/src/firejail/main.c b/src/firejail/main.c
index 2ae3213ee..7afbf9ce3 100644
--- a/src/firejail/main.c
+++ b/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
diff --git a/src/firejail/usage.c b/src/firejail/usage.c
index 9197baae2..d3ebefaae 100644
--- a/src/firejail/usage.c
+++ b/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");
diff --git a/src/firejail/user.c b/src/firejail/user.c
new file mode 100644
index 000000000..e5f7848e8
--- /dev/null
+++ b/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);
+}
diff --git a/src/man/firejail.txt b/src/man/firejail.txt
index 13eccbdce..ef65530db 100644
--- a/src/man/firejail.txt
+++ b/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