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/*
* Copyright (C) 2014-2021 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 "../include/firejail_user.h"
#include <sys/mount.h>
#include <sys/stat.h>
#include <linux/limits.h>
#include <fnmatch.h>
#include <glob.h>
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#ifndef O_PATH
#define O_PATH 010000000
#endif
#define MAXBUF 1024
// linked list of users
typedef struct user_list {
struct user_list *next;
const char *user;
} USER_LIST;
USER_LIST *ulist = NULL;
static void ulist_add(const char *user) {
assert(user);
USER_LIST *nlist = malloc(sizeof(USER_LIST));
if (!nlist)
errExit("malloc");
memset(nlist, 0, sizeof(USER_LIST));
nlist->user = user;
nlist->next = ulist;
ulist = nlist;
}
static USER_LIST *ulist_find(const char *user) {
assert(user);
USER_LIST *ptr = ulist;
while (ptr) {
if (strcmp(ptr->user, user) == 0)
return ptr;
ptr = ptr->next;
}
return NULL;
}
static void sanitize_home(void) {
assert(getuid() != 0); // this code works only for regular users
struct stat s;
if (arg_debug)
printf("Cleaning /home directory\n");
// keep a copy of the user home directory
int fd = safe_fd(cfg.homedir, O_PATH|O_DIRECTORY|O_NOFOLLOW|O_CLOEXEC);
if (fd == -1)
goto errout;
if (fstat(fd, &s) == -1) { // FUSE
if (errno != EACCES)
errExit("fstat");
close(fd);
goto errout;
}
char *proc;
if (asprintf(&proc, "/proc/self/fd/%d", fd) == -1)
errExit("asprintf");
if (mkdir(RUN_WHITELIST_HOME_DIR, 0755) == -1)
errExit("mkdir");
if (mount(proc, RUN_WHITELIST_HOME_DIR, NULL, MS_BIND|MS_REC, NULL) < 0)
errExit("mount bind");
free(proc);
close(fd);
// mount tmpfs in the new home
if (mount("tmpfs", "/home", "tmpfs", MS_NOSUID | MS_NODEV | MS_STRICTATIME, "mode=755,gid=0") < 0)
errExit("mount tmpfs");
selinux_relabel_path("/home", "/home");
fs_logger("tmpfs /home");
// create user home directory
if (mkdir(cfg.homedir, 0755) == -1) {
if (mkpath_as_root(cfg.homedir))
errExit("mkpath");
if (mkdir(cfg.homedir, 0755) == -1)
errExit("mkdir");
selinux_relabel_path(cfg.homedir, cfg.homedir);
}
fs_logger2("mkdir", cfg.homedir);
// set mode and ownership
if (set_perms(cfg.homedir, s.st_uid, s.st_gid, s.st_mode))
errExit("set_perms");
// mount user home directory
if (mount(RUN_WHITELIST_HOME_DIR, cfg.homedir, NULL, MS_BIND|MS_REC, NULL) < 0)
errExit("mount bind");
// mask home dir under /run
if (mount("tmpfs", RUN_WHITELIST_HOME_DIR, "tmpfs", MS_NOSUID | MS_NODEV | MS_STRICTATIME, "mode=755,gid=0") < 0)
errExit("mount tmpfs");
fs_logger2("tmpfs", RUN_WHITELIST_HOME_DIR);
if (!arg_private)
fs_logger2("whitelist", cfg.homedir);
return;
errout:
fwarning("cannot clean /home directory\n");
}
static void sanitize_run(void) {
if (arg_debug)
printf("Cleaning /run/user directory\n");
char *runuser;
if (asprintf(&runuser, "/run/user/%u", getuid()) == -1)
errExit("asprintf");
struct stat s;
if (stat(runuser, &s) == -1) {
// cannot find /user/run/$UID directory, just return
if (arg_debug)
printf("Cannot find %s directory\n", runuser);
free(runuser);
return;
}
if (mkdir(RUN_WHITELIST_RUN_DIR, 0755) == -1)
errExit("mkdir");
// keep a copy of the /run/user/$UID directory
if (mount(runuser, RUN_WHITELIST_RUN_DIR, NULL, MS_BIND|MS_REC, NULL) < 0)
errExit("mount bind");
// mount tmpfs on /run/user
if (mount("tmpfs", "/run/user", "tmpfs", MS_NOSUID | MS_NODEV | MS_STRICTATIME, "mode=755,gid=0") < 0)
errExit("mount tmpfs");
selinux_relabel_path("/run/user", "/run/user");
fs_logger("tmpfs /run/user");
// create new user directory
if (mkdir(runuser, 0700) == -1)
errExit("mkdir");
selinux_relabel_path(runuser, runuser);
fs_logger2("mkdir", runuser);
// set mode and ownership
if (set_perms(runuser, getuid(), getgid(), 0700))
errExit("set_perms");
// mount /run/user/$UID directory
if (mount(RUN_WHITELIST_RUN_DIR, runuser, NULL, MS_BIND|MS_REC, NULL) < 0)
errExit("mount bind");
// mask mirrored /run/user/$UID directory
if (mount("tmpfs", RUN_WHITELIST_RUN_DIR, "tmpfs", MS_NOSUID | MS_NODEV | MS_STRICTATIME, "mode=755,gid=0") < 0)
errExit("mount tmpfs");
fs_logger2("tmpfs", RUN_WHITELIST_RUN_DIR);
free(runuser);
}
static void sanitize_passwd(void) {
struct stat s;
if (stat("/etc/passwd", &s) == -1)
return;
assert(uid_min);
if (arg_debug)
printf("Sanitizing /etc/passwd, UID_MIN %d\n", uid_min);
if (is_link("/etc/passwd")) {
fprintf(stderr, "Error: invalid /etc/passwd\n");
exit(1);
}
FILE *fpin = NULL;
FILE *fpout = NULL;
// open files
/* coverity[toctou] */
fpin = fopen("/etc/passwd", "r");
if (!fpin)
goto errout;
fpout = fopen(RUN_PASSWD_FILE, "w");
if (!fpout)
goto errout;
// read the file line by line
char buf[MAXBUF];
uid_t myuid = getuid();
while (fgets(buf, MAXBUF, fpin)) {
// comments and empty lines
if (*buf == '\0' || *buf == '#')
continue;
// sample line:
// www-data:x:33:33:www-data:/var/www:/bin/sh
// drop lines with uid > 1000 and not the current user
char *ptr = buf;
// advance to uid
while (*ptr != ':' && *ptr != '\0')
ptr++;
if (*ptr == '\0')
goto errout;
char *ptr1 = ptr;
ptr++;
while (*ptr != ':' && *ptr != '\0')
ptr++;
if (*ptr == '\0')
goto errout;
ptr++;
if (*ptr == '\0')
goto errout;
// process uid
int uid;
int rv = sscanf(ptr, "%d:", &uid);
if (rv == 0 || uid < 0)
goto errout;
assert(uid_min);
if (uid < uid_min || uid == 65534) { // on Debian platforms user nobody is 65534
fprintf(fpout, "%s", buf);
continue;
}
if ((uid_t) uid != myuid) {
// store user name - necessary to process /etc/group
*ptr1 = '\0';
char *user = strdup(buf);
if (!user)
errExit("malloc");
ulist_add(user);
continue; // skip line
}
fprintf(fpout, "%s", buf);
}
fclose(fpin);
SET_PERMS_STREAM(fpout, 0, 0, 0644);
fclose(fpout);
// mount-bind tne new password file
if (mount(RUN_PASSWD_FILE, "/etc/passwd", "none", MS_BIND, "mode=400,gid=0") < 0)
errExit("mount");
fs_logger("create /etc/passwd");
return;
errout:
fwarning("failed to clean up /etc/passwd\n");
if (fpin)
fclose(fpin);
if (fpout)
fclose(fpout);
}
// returns 1 if fails, 0 if OK
static int copy_line(FILE *fpout, char *buf, char *ptr) {
// fpout: GROUP_FILE
// buf: pulse:x:115:netblue,bingo
// ptr: 115:neblue,bingo
while (*ptr != ':' && *ptr != '\0')
ptr++;
if (*ptr == '\0')
return 1;
ptr++;
if (*ptr == '\n' || *ptr == '\0') {
fprintf(fpout, "%s", buf);
return 0;
}
// print what we have so far
char tmp = *ptr;
*ptr = '\0';
fprintf(fpout, "%s", buf);
*ptr = tmp;
// tokenize
char *token = strtok(ptr, ",\n");
int first = 1;
while (token) {
char *newtoken = strtok(NULL, ",\n");
if (ulist_find(token)) {
//skip
token = newtoken;
continue;
}
if (!first)
fprintf(fpout, ",");
first = 0;
fprintf(fpout, "%s", token);
token = newtoken;
}
fprintf(fpout, "\n");
return 0;
}
static void sanitize_group(void) {
struct stat s;
if (stat("/etc/group", &s) == -1)
return;
assert(gid_min);
if (arg_debug)
printf("Sanitizing /etc/group, GID_MIN %d\n", gid_min);
if (is_link("/etc/group")) {
fprintf(stderr, "Error: invalid /etc/group\n");
exit(1);
}
FILE *fpin = NULL;
FILE *fpout = NULL;
// open files
/* coverity[toctou] */
fpin = fopen("/etc/group", "r");
if (!fpin)
goto errout;
fpout = fopen(RUN_GROUP_FILE, "w");
if (!fpout)
goto errout;
// read the file line by line
char buf[MAXBUF];
gid_t mygid = getgid();
while (fgets(buf, MAXBUF, fpin)) {
// comments and empty lines
if (*buf == '\0' || *buf == '#')
continue;
// sample line:
// pulse:x:115:netblue,bingo
// drop lines with uid > 1000 and not the current user group
char *ptr = buf;
// advance to uid
while (*ptr != ':' && *ptr != '\0')
ptr++;
if (*ptr == '\0')
goto errout;
ptr++;
while (*ptr != ':' && *ptr != '\0')
ptr++;
if (*ptr == '\0')
goto errout;
ptr++;
if (*ptr == '\0')
goto errout;
// process uid
int gid;
int rv = sscanf(ptr, "%d:", &gid);
if (rv == 0 || gid < 0)
goto errout;
assert(gid_min);
if (gid < gid_min || gid == 65534) { // on Debian platforms 65534 is group nogroup
if (copy_line(fpout, buf, ptr))
goto errout;
continue;
}
if ((gid_t) gid != mygid) {
continue; // skip line
}
if (copy_line(fpout, buf, ptr))
goto errout;
}
fclose(fpin);
SET_PERMS_STREAM(fpout, 0, 0, 0644);
fclose(fpout);
// mount-bind tne new group file
if (mount(RUN_GROUP_FILE, "/etc/group", "none", MS_BIND, "mode=400,gid=0") < 0)
errExit("mount");
fs_logger("create /etc/group");
return;
errout:
fwarning("failed to clean up /etc/group\n");
if (fpin)
fclose(fpin);
if (fpout)
fclose(fpout);
}
void restrict_users(void) {
if (arg_allusers)
return;
// only in user mode
if (getuid()) {
if (strncmp(cfg.homedir, "/home/", 6) == 0) {
// user has the home directory under /home
sanitize_home();
}
else {
// user has the home directory outside /home
// mount tmpfs on top of /home in order to hide it
if (mount("tmpfs", "/home", "tmpfs", MS_NOSUID | MS_NODEV | MS_STRICTATIME, "mode=755,gid=0") < 0)
errExit("mount tmpfs");
fs_logger("tmpfs /home");
}
sanitize_run();
sanitize_passwd();
sanitize_group();
}
}
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