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/*
* Copyright (C) 2014-2017 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/stat.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/prctl.h>
#include <errno.h>
static int apply_caps = 0;
static uint64_t caps = 0;
static int apply_seccomp = 0;
static unsigned display = 0;
#define BUFLEN 4096
static void signal_handler(int sig){
flush_stdin();
exit(sig);
}
static void extract_x11_display(pid_t pid) {
char *fname;
if (asprintf(&fname, "%s/%d", RUN_FIREJAIL_X11_DIR, pid) == -1)
errExit("asprintf");
FILE *fp = fopen(fname, "r");
free(fname);
if (!fp)
return;
if (1 != fscanf(fp, "%d", &display)) {
fprintf(stderr, "Error: cannot read X11 display file\n");
fclose(fp);
return;
}
fclose(fp);
// check display range
if (display < X11_DISPLAY_START || display > X11_DISPLAY_END) {
fprintf(stderr, "Error: invalid X11 display range\n");
return;
}
// store the display number for join process in /run/firejail/x11
EUID_ROOT();
set_x11_file(getpid(), display);
EUID_USER();
}
static void extract_command(int argc, char **argv, int index) {
EUID_ASSERT();
if (index >= argc)
return;
// doubledash followed by positional parameters
if (strcmp(argv[index], "--") == 0) {
arg_doubledash = 1;
index++;
if (index >= argc)
return;
}
// first argv needs to be a valid command
if (arg_doubledash == 0 && *argv[index] == '-') {
fprintf(stderr, "Error: invalid option %s after --join\n", argv[index]);
exit(1);
}
// build command
build_cmdline(&cfg.command_line, &cfg.window_title, argc, argv, index);
if (arg_debug)
printf("Extracted command #%s#\n", cfg.command_line);
}
static void extract_nogroups(pid_t pid) {
char *fname;
if (asprintf(&fname, "/proc/%d/root%s", pid, RUN_GROUPS_CFG) == -1)
errExit("asprintf");
struct stat s;
if (stat(fname, &s) == -1)
return;
arg_nogroups = 1;
free(fname);
}
static void extract_cpu(pid_t pid) {
char *fname;
if (asprintf(&fname, "/proc/%d/root%s", pid, RUN_CPU_CFG) == -1)
errExit("asprintf");
struct stat s;
if (stat(fname, &s) == -1)
return;
// there is a CPU_CFG file, load it!
load_cpu(fname);
free(fname);
}
static void extract_cgroup(pid_t pid) {
char *fname;
if (asprintf(&fname, "/proc/%d/root%s", pid, RUN_CGROUP_CFG) == -1)
errExit("asprintf");
struct stat s;
if (stat(fname, &s) == -1)
return;
// there is a cgroup file CGROUP_CFG, load it!
load_cgroup(fname);
free(fname);
}
static void extract_caps_seccomp(pid_t pid) {
// open stat file
char *file;
if (asprintf(&file, "/proc/%u/status", pid) == -1) {
perror("asprintf");
exit(1);
}
FILE *fp = fopen(file, "r");
if (!fp) {
free(file);
fprintf(stderr, "Error: cannot open stat file for process %u\n", pid);
exit(1);
}
char buf[BUFLEN];
while (fgets(buf, BUFLEN - 1, fp)) {
if (strncmp(buf, "Seccomp:", 8) == 0) {
char *ptr = buf + 8;
int val;
sscanf(ptr, "%d", &val);
if (val == 2)
apply_seccomp = 1;
break;
}
else if (strncmp(buf, "CapBnd:", 7) == 0) {
char *ptr = buf + 7;
unsigned long long val;
sscanf(ptr, "%llx", &val);
apply_caps = 1;
caps = val;
}
}
fclose(fp);
free(file);
}
static void extract_user_namespace(pid_t pid) {
// test user namespaces available in the kernel
struct stat s1;
struct stat s2;
struct stat s3;
if (stat("/proc/self/ns/user", &s1) == 0 &&
stat("/proc/self/uid_map", &s2) == 0 &&
stat("/proc/self/gid_map", &s3) == 0);
else
return;
// read uid map
char *uidmap;
if (asprintf(&uidmap, "/proc/%u/uid_map", pid) == -1)
errExit("asprintf");
FILE *fp = fopen(uidmap, "r");
if (!fp) {
free(uidmap);
return;
}
// check uid map
int u1;
int u2;
if (fscanf(fp, "%d %d", &u1, &u2) == 2) {
if (arg_debug)
printf("User namespace detected: %s, %d, %d\n", uidmap, u1, u2);
if (u1 != 0 || u2 != 0)
arg_noroot = 1;
}
fclose(fp);
free(uidmap);
}
void join(pid_t pid, int argc, char **argv, int index) {
EUID_ASSERT();
char *homedir = cfg.homedir;
pid_t parent = pid;
extract_command(argc, argv, index);
signal (SIGTERM, signal_handler);
// if the pid is that of a firejail process, use the pid of the first child process
EUID_ROOT();
char *comm = pid_proc_comm(pid);
EUID_USER();
if (comm) {
if (strcmp(comm, "firejail") == 0) {
pid_t child;
if (find_child(pid, &child) == 0) {
pid = child;
if (!arg_quiet)
printf("Switching to pid %u, the first child process inside the sandbox\n", (unsigned) pid);
}
}
free(comm);
}
// check privileges for non-root users
uid_t uid = getuid();
if (uid != 0) {
uid_t sandbox_uid = pid_get_uid(pid);
if (uid != sandbox_uid) {
fprintf(stderr, "Error: permission is denied to join a sandbox created by a different user.\n");
exit(1);
}
}
extract_x11_display(parent);
EUID_ROOT();
// in user mode set caps seccomp, cpu, cgroup, etc
if (getuid() != 0) {
extract_caps_seccomp(pid);
extract_cpu(pid);
extract_cgroup(pid);
extract_nogroups(pid);
extract_user_namespace(pid);
}
// set cgroup
if (cfg.cgroup) // not available for uid 0
set_cgroup(cfg.cgroup);
// join namespaces
if (arg_join_network) {
if (join_namespace(pid, "net"))
exit(1);
}
else if (arg_join_filesystem) {
if (join_namespace(pid, "mnt"))
exit(1);
}
else {
if (join_namespace(pid, "ipc") ||
join_namespace(pid, "net") ||
join_namespace(pid, "pid") ||
join_namespace(pid, "uts") ||
join_namespace(pid, "mnt"))
exit(1);
}
pid_t child = fork();
if (child < 0)
errExit("fork");
if (child == 0) {
// drop discretionary access control capabilities for root sandboxes
caps_drop_dac_override();
// chroot into /proc/PID/root directory
char *rootdir;
if (asprintf(&rootdir, "/proc/%d/root", pid) == -1)
errExit("asprintf");
int rv;
if (!arg_join_network) {
rv = chroot(rootdir); // this will fail for processes in sandboxes not started with --chroot option
if (rv == 0)
printf("changing root to %s\n", rootdir);
}
prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0); // kill the child in case the parent died
if (chdir("/") < 0)
errExit("chdir");
if (homedir) {
struct stat s;
if (stat(homedir, &s) == 0) {
/* coverity[toctou] */
if (chdir(homedir) < 0)
errExit("chdir");
}
}
// set cpu affinity
if (cfg.cpus) // not available for uid 0
set_cpu_affinity();
// set caps filter
if (apply_caps == 1) // not available for uid 0
caps_set(caps);
#ifdef HAVE_SECCOMP
// read cfg.protocol from file
if (getuid() != 0)
protocol_filter_load(RUN_PROTOCOL_CFG);
if (cfg.protocol) { // not available for uid 0
seccomp_load(RUN_SECCOMP_PROTOCOL); // install filter
}
// set seccomp filter
if (apply_seccomp == 1) // not available for uid 0
seccomp_load(RUN_SECCOMP_CFG);
#endif
// mount user namespace or drop privileges
if (arg_noroot) { // not available for uid 0
if (arg_debug)
printf("Joining user namespace\n");
if (join_namespace(1, "user"))
exit(1);
// user namespace resets capabilities
// set caps filter
if (apply_caps == 1) // not available for uid 0
caps_set(caps);
}
else
drop_privs(arg_nogroups); // nogroups not available for uid 0
// set nice
if (arg_nice) {
errno = 0;
int rv = nice(cfg.nice);
(void) rv;
if (errno) {
fwarning("cannot set nice value\n");
errno = 0;
}
}
// set environment, add x11 display
env_defaults();
if (display) {
char *display_str;
if (asprintf(&display_str, ":%d", display) == -1)
errExit("asprintf");
setenv("DISPLAY", display_str, 1);
free(display_str);
}
if (cfg.command_line == NULL) {
assert(cfg.shell);
cfg.command_line = cfg.shell;
cfg.window_title = cfg.shell;
}
int cwd = 0;
if (cfg.cwd) {
if (chdir(cfg.cwd) == 0)
cwd = 1;
}
if (!cwd) {
if (chdir("/") < 0)
errExit("chdir");
if (cfg.homedir) {
struct stat s;
if (stat(cfg.homedir, &s) == 0) {
/* coverity[toctou] */
if (chdir(cfg.homedir) < 0)
errExit("chdir");
}
}
}
start_application(0);
// it will never get here!!!
}
// wait for the child to finish
waitpid(child, NULL, 0);
flush_stdin();
exit(0);
}
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