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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/types.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <fcntl.h>
#include <unistd.h>
#include <signal.h>
#include <stdlib.h>
#include <dirent.h>
#include <sys/mount.h>
#include <sys/wait.h>
#include <errno.h>
#include <limits.h>
// Parse the DISPLAY environment variable and return a display number.
// Returns -1 if DISPLAY is not set, or is set to anything other than :ddd.
int x11_display(void) {
const char *display_str = getenv("DISPLAY");
char *endp;
unsigned long display;
if (!display_str) {
if (arg_debug)
fputs("DISPLAY is not set\n", stderr);
return -1;
}
if (display_str[0] != ':' || display_str[1] < '0' || display_str[1] > '9') {
if (arg_debug)
fprintf(stderr, "unsupported DISPLAY form '%s'\n", display_str);
return -1;
}
errno = 0;
display = strtoul(display_str+1, &endp, 10);
// handling DISPLAY=:0 and also :0.0
if (endp == display_str+1 || (*endp != '\0' && *endp != '.')) {
if (arg_debug)
fprintf(stderr, "unsupported DISPLAY form '%s'\n", display_str);
return -1;
}
if (errno || display > (unsigned long)INT_MAX) {
if (arg_debug)
fprintf(stderr, "display number %s is outside the valid range\n",
display_str+1);
return -1;
}
if (arg_debug)
fprintf(stderr, "DISPLAY=%s parsed as %lu\n", display_str, display);
return (int)display;
}
#ifdef HAVE_X11
// check for X11 abstract sockets
static int x11_abstract_sockets_present(void) {
EUID_ROOT(); // grsecurity fix
FILE *fp = fopen("/proc/net/unix", "r");
if (!fp)
errExit("fopen");
EUID_USER();
char *linebuf = 0;
size_t bufsz = 0;
int found = 0;
errno = 0;
for (;;) {
if (getline(&linebuf, &bufsz, fp) == -1) {
if (errno)
errExit("getline");
break;
}
// The last space-separated field in 'linebuf' is the
// pathname of the socket. Abstract sockets' pathnames
// all begin with '@/', normal ones begin with '/'.
char *p = strrchr(linebuf, ' ');
if (!p) {
fputs("error parsing /proc/net/unix\n", stderr);
exit(1);
}
if (strncmp(p+1, "@/tmp/.X11-unix/", 16) == 0) {
found = 1;
break;
}
}
free(linebuf);
fclose(fp);
return found;
}
// Choose a random, unallocated display number. This has an inherent
// and unavoidable TOCTOU race, since we cannot create either the
// socket or a lockfile ourselves.
static int random_display_number(void) {
int display;
int found = 0;
int i;
struct sockaddr_un sa;
// The -1 here is because we need space to inject a
// leading nul byte.
int sun_pathmax = (int)(sizeof sa.sun_path - 1);
assert((size_t)sun_pathmax == sizeof sa.sun_path - 1);
int sun_pathlen;
int sockfd = socket(AF_UNIX, SOCK_STREAM, 0);
if (sockfd == -1)
errExit("socket");
for (i = 0; i < 100; i++) {
// We try display numbers in the range 21 through 1000.
// Normal X servers typically use displays in the 0-10 range;
// ssh's X11 forwarding uses 10-20, and login screens
// (e.g. gdm3) may use displays above 1000.
display = rand() % 979 + 21;
// The display number might be claimed by a server listening
// in _either_ the normal or the abstract namespace; they
// don't necessarily do both. The easiest way to check is
// to try to connect, both ways.
memset(&sa, 0, sizeof sa);
sa.sun_family = AF_UNIX;
sun_pathlen = snprintf(sa.sun_path, sun_pathmax,
"/tmp/.X11-unix/X%d", display);
if (sun_pathlen >= sun_pathmax) {
fprintf(stderr, "sun_path too small for display :%d"
" (only %d bytes usable)\n", display, sun_pathmax);
exit(1);
}
if (connect(sockfd, (struct sockaddr *)&sa,
offsetof(struct sockaddr_un, sun_path) + sun_pathlen + 1) == 0) {
close(sockfd);
sockfd = socket(AF_UNIX, SOCK_STREAM, 0);
if (sockfd == -1)
errExit("socket");
continue;
}
if (errno != ECONNREFUSED && errno != ENOENT)
errExit("connect");
// Name not claimed in the normal namespace; now try it
// in the abstract namespace. Note that abstract-namespace
// names are NOT nul-terminated; they extend to the length
// specified as the third argument to 'connect'.
memmove(sa.sun_path + 1, sa.sun_path, sun_pathlen + 1);
sa.sun_path[0] = '\0';
if (connect(sockfd, (struct sockaddr *)&sa,
offsetof(struct sockaddr_un, sun_path) + 1 + sun_pathlen) == 0) {
close(sockfd);
sockfd = socket(AF_UNIX, SOCK_STREAM, 0);
if (sockfd == -1)
errExit("socket");
continue;
}
if (errno != ECONNREFUSED && errno != ENOENT)
errExit("connect");
// This display number is unclaimed. Of course, it could
// be claimed before we get around to doing it...
found = 1;
break;
}
close(sockfd);
if (!found) {
fputs("Error: cannot find an unallocated X11 display number, "
"exiting...\n", stderr);
exit(1);
}
return display;
}
#endif
#ifdef HAVE_X11
void x11_start_xvfb(int argc, char **argv) {
EUID_ASSERT();
int i;
struct stat s;
pid_t jail = 0;
pid_t server = 0;
setenv("FIREJAIL_X11", "yes", 1);
// mever try to run X servers as root!!!
if (getuid() == 0) {
fprintf(stderr, "Error: X11 sandboxing is not available when running as root\n");
exit(1);
}
drop_privs(0);
// check xephyr
if (!program_in_path("Xvfb")) {
fprintf(stderr, "\nError: Xvfb program was not found in /usr/bin directory, please install it:\n");
fprintf(stderr, " Debian/Ubuntu/Mint: sudo apt-get install xvfb\n");
fprintf(stderr, " Arch: sudo pacman -S xorg-server-xvfb\n");
exit(0);
}
int display = random_display_number();
char *display_str;
if (asprintf(&display_str, ":%d", display) == -1)
errExit("asprintf");
assert(xvfb_screen);
char *server_argv[256] = { // rest initialyzed to NULL
"Xvfb", display_str, "-screen", "0", xvfb_screen
};
unsigned pos = 0;
while (server_argv[pos] != NULL) pos++;
assert(xvfb_extra_params); // should be "" if empty
// parse xvfb_extra_params
// very basic quoting support
char *temp = strdup(xephyr_extra_params);
if (*xephyr_extra_params != '\0') {
if (!temp)
errExit("strdup");
bool dquote = false;
bool squote = false;
for (i = 0; i < (int) strlen(xvfb_extra_params); i++) {
if (temp[i] == '\"') {
dquote = !dquote;
// replace closing quote by \0
if (dquote) temp[i] = '\0';
}
if (temp[i] == '\'') {
squote = !squote;
// replace closing quote by \0
if (squote) temp[i] = '\0';
}
if (!dquote && !squote && temp[i] == ' ') temp[i] = '\0';
if (dquote && squote) {
fprintf(stderr, "Error: mixed quoting found while parsing xvfb_extra_params\n");
exit(1);
}
}
if (dquote) {
fprintf(stderr, "Error: unclosed quote found while parsing xephyr_extra_params\n");
exit(1);
}
for (i = 0; i < (int) strlen(xvfb_extra_params)-1; i++) {
if (pos >= (sizeof(server_argv)/sizeof(*server_argv)) - 2) {
fprintf(stderr, "Error: arg count limit exceeded while parsing xvfb_extra_params\n");
exit(1);
}
if (temp[i] == '\0' && (temp[i+1] == '\"' || temp[i+1] == '\'')) server_argv[pos++] = temp + i + 2;
else if (temp[i] == '\0' && temp[i+1] != '\0') server_argv[pos++] = temp + i + 1;
}
}
server_argv[pos++] = NULL;
assert(pos < (sizeof(server_argv)/sizeof(*server_argv))); // no overrun
assert(server_argv[pos-1] == NULL); // last element is null
if (arg_debug) {
size_t i = 0;
printf("xvfb server:");
while (server_argv[i]!=NULL) {
printf(" \"%s\"", server_argv[i]);
i++;
}
putchar('\n');
}
// remove --x11 arg
char *jail_argv[argc+2];
int j = 0;
for (i = 0; i < argc; i++) {
if (strncmp(argv[i], "--x11", 5) == 0)
continue;
jail_argv[j] = argv[i];
j++;
}
jail_argv[j] = NULL;
assert(j < argc+2); // no overrun
if (arg_debug) {
size_t i = 0;
printf("xvfb client:");
while (jail_argv[i]!=NULL) {
printf(" \"%s\"", jail_argv[i]);
i++;
}
putchar('\n');
}
server = fork();
if (server < 0)
errExit("fork");
if (server == 0) {
if (arg_debug)
printf("Starting xvfb...\n");
// running without privileges - see drop_privs call above
assert(getenv("LD_PRELOAD") == NULL);
execvp(server_argv[0], server_argv);
perror("execvp");
_exit(1);
}
if (arg_debug)
printf("xephyr server pid %d\n", server);
// check X11 socket
char *fname;
if (asprintf(&fname, "/tmp/.X11-unix/X%d", display) == -1)
errExit("asprintf");
int n = 0;
// wait for x11 server to start
while (++n < 10) {
sleep(1);
if (stat(fname, &s) == 0)
break;
};
if (n == 10) {
fprintf(stderr, "Error: failed to start xephyr\n");
exit(1);
}
free(fname);
if (arg_debug) {
printf("X11 sockets: "); fflush(0);
int rv = system("ls /tmp/.X11-unix");
(void) rv;
}
assert(display_str);
setenv("DISPLAY", display_str, 1);
// run attach command
jail = fork();
if (jail < 0)
errExit("fork");
if (jail == 0) {
if (!arg_quiet)
printf("\n*** Attaching to Xvfb display %d ***\n\n", display);
// running without privileges - see drop_privs call above
assert(getenv("LD_PRELOAD") == NULL);
execvp(jail_argv[0], jail_argv);
perror("execvp");
_exit(1);
}
// cleanup
free(display_str);
free(temp);
// wait for either server or jail termination
pid_t pid = wait(NULL);
// see which process terminated and kill other
if (pid == server) {
kill(jail, SIGTERM);
}
else if (pid == jail) {
kill(server, SIGTERM);
}
// without this closing Xephyr window may mess your terminal:
// "monitoring" process will release terminal before
// jail process ends and releases terminal
wait(NULL); // fulneral
exit(0);
}
//$ Xephyr -ac -br -noreset -screen 800x600 :22 &
//$ DISPLAY=:22 firejail --net=eth0 --blacklist=/tmp/.X11-unix/x0 firefox
void x11_start_xephyr(int argc, char **argv) {
EUID_ASSERT();
int i;
struct stat s;
pid_t jail = 0;
pid_t server = 0;
setenv("FIREJAIL_X11", "yes", 1);
// unfortunately, xephyr does a number of weird things when started by root user!!!
if (getuid() == 0) {
fprintf(stderr, "Error: X11 sandboxing is not available when running as root\n");
exit(1);
}
drop_privs(0);
// check xephyr
if (!program_in_path("Xephyr")) {
fprintf(stderr, "\nError: Xephyr program was not found in /usr/bin directory, please install it:\n");
fprintf(stderr, " Debian/Ubuntu/Mint: sudo apt-get install xserver-xephyr\n");
fprintf(stderr, " Arch: sudo pacman -S xorg-server-xephyr\n");
exit(0);
}
int display = random_display_number();
char *display_str;
if (asprintf(&display_str, ":%d", display) == -1)
errExit("asprintf");
assert(xephyr_screen);
char *server_argv[256] = { // rest initialyzed to NULL
"Xephyr", "-ac", "-br", "-noreset", "-screen", xephyr_screen
};
unsigned pos = 0;
while (server_argv[pos] != NULL) pos++;
if (checkcfg(CFG_XEPHYR_WINDOW_TITLE)) {
server_argv[pos++] = "-title";
server_argv[pos++] = "firejail x11 sandbox";
}
assert(xephyr_extra_params); // should be "" if empty
// parse xephyr_extra_params
// very basic quoting support
char *temp = strdup(xephyr_extra_params);
if (*xephyr_extra_params != '\0') {
if (!temp)
errExit("strdup");
bool dquote = false;
bool squote = false;
for (i = 0; i < (int) strlen(xephyr_extra_params); i++) {
if (temp[i] == '\"') {
dquote = !dquote;
// replace closing quote by \0
if (dquote) temp[i] = '\0';
}
if (temp[i] == '\'') {
squote = !squote;
// replace closing quote by \0
if (squote) temp[i] = '\0';
}
if (!dquote && !squote && temp[i] == ' ') temp[i] = '\0';
if (dquote && squote) {
fprintf(stderr, "Error: mixed quoting found while parsing xephyr_extra_params\n");
exit(1);
}
}
if (dquote) {
fprintf(stderr, "Error: unclosed quote found while parsing xephyr_extra_params\n");
exit(1);
}
for (i = 0; i < (int) strlen(xephyr_extra_params)-1; i++) {
if (pos >= (sizeof(server_argv)/sizeof(*server_argv)) - 2) {
fprintf(stderr, "Error: arg count limit exceeded while parsing xephyr_extra_params\n");
exit(1);
}
if (temp[i] == '\0' && (temp[i+1] == '\"' || temp[i+1] == '\'')) server_argv[pos++] = temp + i + 2;
else if (temp[i] == '\0' && temp[i+1] != '\0') server_argv[pos++] = temp + i + 1;
}
}
server_argv[pos++] = display_str;
server_argv[pos++] = NULL;
// no overrun
assert(pos < (sizeof(server_argv)/sizeof(*server_argv)));
assert(server_argv[pos-1] == NULL); // last element is null
if (arg_debug) {
size_t i = 0;
printf("xephyr server:");
while (server_argv[i]!=NULL) {
printf(" \"%s\"", server_argv[i]);
i++;
}
putchar('\n');
}
// remove --x11 arg
char *jail_argv[argc+2];
int j = 0;
for (i = 0; i < argc; i++) {
if (strncmp(argv[i], "--x11", 5) == 0)
continue;
jail_argv[j] = argv[i];
j++;
}
jail_argv[j] = NULL;
assert(j < argc+2); // no overrun
if (arg_debug) {
size_t i = 0;
printf("xephyr client:");
while (jail_argv[i]!=NULL) {
printf(" \"%s\"", jail_argv[i]);
i++;
}
putchar('\n');
}
server = fork();
if (server < 0)
errExit("fork");
if (server == 0) {
if (arg_debug)
printf("Starting xephyr...\n");
// running without privileges - see drop_privs call above
assert(getenv("LD_PRELOAD") == NULL);
execvp(server_argv[0], server_argv);
perror("execvp");
_exit(1);
}
if (arg_debug)
printf("xephyr server pid %d\n", server);
// check X11 socket
char *fname;
if (asprintf(&fname, "/tmp/.X11-unix/X%d", display) == -1)
errExit("asprintf");
int n = 0;
// wait for x11 server to start
while (++n < 10) {
sleep(1);
if (stat(fname, &s) == 0)
break;
};
if (n == 10) {
fprintf(stderr, "Error: failed to start xephyr\n");
exit(1);
}
free(fname);
if (arg_debug) {
printf("X11 sockets: "); fflush(0);
int rv = system("ls /tmp/.X11-unix");
(void) rv;
}
setenv("DISPLAY", display_str, 1);
// run attach command
jail = fork();
if (jail < 0)
errExit("fork");
if (jail == 0) {
if (!arg_quiet)
printf("\n*** Attaching to Xephyr display %d ***\n\n", display);
// running without privileges - see drop_privs call above
assert(getenv("LD_PRELOAD") == NULL);
execvp(jail_argv[0], jail_argv);
perror("execvp");
_exit(1);
}
// cleanup
free(display_str);
free(temp);
// wait for either server or jail termination
pid_t pid = wait(NULL);
// see which process terminated and kill other
if (pid == server) {
kill(jail, SIGTERM);
}
else if (pid == jail) {
kill(server, SIGTERM);
}
// without this closing Xephyr window may mess your terminal:
// "monitoring" process will release terminal before
// jail process ends and releases terminal
wait(NULL); // fulneral
exit(0);
}
void x11_start_xpra(int argc, char **argv) {
EUID_ASSERT();
int i;
struct stat s;
pid_t client = 0;
pid_t server = 0;
setenv("FIREJAIL_X11", "yes", 1);
// unfortunately, xpra does a number of weird things when started by root user!!!
if (getuid() == 0) {
fprintf(stderr, "Error: X11 sandboxing is not available when running as root\n");
exit(1);
}
drop_privs(0);
// check xpra
if (!program_in_path("xpra")) {
fprintf(stderr, "\nError: Xpra program was not found in /usr/bin directory, please install it:\n");
fprintf(stderr, " Debian/Ubuntu/Mint: sudo apt-get install xpra\n");
exit(0);
}
int display = random_display_number();
char *display_str;
if (asprintf(&display_str, ":%d", display) == -1)
errExit("asprintf");
// build the start command
char *server_argv[] = { "xpra", "start", display_str, "--no-daemon", NULL };
int fd_null = -1;
if (arg_quiet) {
fd_null = open("/dev/null", O_RDWR);
if (fd_null == -1)
errExit("open");
}
// start
server = fork();
if (server < 0)
errExit("fork");
if (server == 0) {
if (arg_debug)
printf("Starting xpra...\n");
if (arg_quiet && fd_null != -1) {
dup2(fd_null,0);
dup2(fd_null,1);
dup2(fd_null,2);
}
// running without privileges - see drop_privs call above
assert(getenv("LD_PRELOAD") == NULL);
execvp(server_argv[0], server_argv);
perror("execvp");
_exit(1);
}
// add a small delay, on some systems it takes some time for the server to start
sleep(1);
// check X11 socket
char *fname;
if (asprintf(&fname, "/tmp/.X11-unix/X%d", display) == -1)
errExit("asprintf");
int n = 0;
// wait for x11 server to start
while (++n < 10) {
sleep(1);
if (stat(fname, &s) == 0)
break;
}
if (n == 10) {
fprintf(stderr, "Error: failed to start xpra\n");
exit(1);
}
free(fname);
if (arg_debug) {
printf("X11 sockets: "); fflush(0);
int rv = system("ls /tmp/.X11-unix");
(void) rv;
}
// build attach command
char *attach_argv[] = { "xpra", "--title=\"firejail x11 sandbox\"", "attach", display_str, NULL };
// run attach command
client = fork();
if (client < 0)
errExit("fork");
if (client == 0) {
if (arg_quiet && fd_null != -1) {
dup2(fd_null,0);
dup2(fd_null,1);
dup2(fd_null,2);
}
if (!arg_quiet)
printf("\n*** Attaching to xpra display %d ***\n\n", display);
// running without privileges - see drop_privs call above
assert(getenv("LD_PRELOAD") == NULL);
execvp(attach_argv[0], attach_argv);
perror("execvp");
_exit(1);
}
setenv("DISPLAY", display_str, 1);
// build jail command
char *firejail_argv[argc+2];
int pos = 0;
for (i = 0; i < argc; i++) {
if (strncmp(argv[i], "--x11", 5) == 0)
continue;
firejail_argv[pos] = argv[i];
pos++;
}
firejail_argv[pos] = NULL;
assert(pos < (argc+2));
assert(!firejail_argv[pos]);
// start jail
pid_t jail = fork();
if (jail < 0)
errExit("fork");
if (jail == 0) {
// running without privileges - see drop_privs call above
assert(getenv("LD_PRELOAD") == NULL);
if (firejail_argv[0]) // shut up llvm scan-build
execvp(firejail_argv[0], firejail_argv);
perror("execvp");
exit(1);
}
if (!arg_quiet)
printf("Xpra server pid %d, xpra client pid %d, jail %d\n", server, client, jail);
sleep(1); // adding a delay in order to let the server start
// wait for jail or server to end
while (1) {
pid_t pid = wait(NULL);
if (pid == jail) {
char *stop_argv[] = { "xpra", "stop", display_str, NULL };
pid_t stop = fork();
if (stop < 0)
errExit("fork");
if (stop == 0) {
if (arg_quiet && fd_null != -1) {
dup2(fd_null,0);
dup2(fd_null,1);
dup2(fd_null,2);
}
// running without privileges - see drop_privs call above
assert(getenv("LD_PRELOAD") == NULL);
execvp(stop_argv[0], stop_argv);
perror("execvp");
_exit(1);
}
// wait for xpra server to stop, 10 seconds limit
while (++n < 10) {
sleep(1);
pid = waitpid(server, NULL, WNOHANG);
if (pid == server)
break;
}
if (arg_debug) {
if (n == 10)
printf("failed to stop xpra server gratefully\n");
else
printf("xpra server successfully stopped in %d secs\n", n);
}
// kill xpra server and xpra client
kill(client, SIGTERM);
kill(server, SIGTERM);
exit(0);
}
else if (pid == server) {
// kill firejail process
kill(jail, SIGTERM);
// kill xpra client (should die with server, but...)
kill(client, SIGTERM);
exit(0);
}
}
}
void x11_start(int argc, char **argv) {
EUID_ASSERT();
// unfortunately, xpra does a number of weird things when started by root user!!!
if (getuid() == 0) {
fprintf(stderr, "Error: X11 sandboxing is not available when running as root\n");
exit(1);
}
// check xpra
if (program_in_path("xpra"))
x11_start_xpra(argc, argv);
else if (program_in_path("Xephyr"))
x11_start_xephyr(argc, argv);
else {
fprintf(stderr, "\nError: Xpra or Xephyr not found in /usr/bin directory, please install one of them:\n");
fprintf(stderr, " Debian/Ubuntu/Mint: sudo apt-get install xpra\n");
fprintf(stderr, " Debian/Ubuntu/Mint: sudo apt-get install xserver-xephyr\n");
exit(0);
}
}
#endif
// Porting notes:
//
// 1. merge #1100 from zackw:
// Attempting to run xauth -f directly on a file in /run/firejail/mnt/ directory fails on Debian 8
// with this message:
// xauth: timeout in locking authority file /run/firejail/mnt/sec.Xauthority-Qt5Mu4
// Failed to create untrusted X cookie: xauth: exit 1
// For this reason we run xauth on a file in a tmpfs filesystem mounted on /tmp. This was
// a partial merge.
//
// 2. Since we cannot deal with the TOCTOU condition when mounting .Xauthority in user home
// directory, we need to make sure /usr/bin/xauth executable is the real thing, and not
// something picked up on $PATH.
//
// 3. If for any reason xauth command fails, we exit the sandbox. On Debian 8 this happens
// when using a network namespace. Somehow, xauth tries to connect to the abstract socket,
// and it fails because of the network namespace - it should try to connect to the regular
// Unix socket! If we ignore the fail condition, the program will be started on X server without
// the security extension loaded.
void x11_xorg(void) {
#ifdef HAVE_X11
// check xauth utility is present in the system
struct stat s;
if (stat("/usr/bin/xauth", &s) == -1) {
fprintf(stderr, "Error: xauth utility not found in PATH. Please install it:\n"
" Debian/Ubuntu/Mint: sudo apt-get install xauth\n");
exit(1);
}
if (s.st_uid != 0 && s.st_gid != 0) {
fprintf(stderr, "Error: invalid /usr/bin/xauth executable\n");
exit(1);
}
// get DISPLAY env
char *display = getenv("DISPLAY");
if (!display) {
fputs("Error: --x11=xorg requires an 'outer' X11 server to use.\n", stderr);
exit(1);
}
// temporarily mount a tempfs on top of /tmp directory
if (mount("tmpfs", "/tmp", "tmpfs", MS_NOSUID | MS_STRICTATIME | MS_REC, "mode=777,gid=0") < 0)
errExit("mounting /tmp");
// create the temporary .Xauthority file
if (arg_debug)
printf("Generating a new .Xauthority file\n");
char tmpfname[] = "/tmp/.tmpXauth-XXXXXX";
int fd = mkstemp(tmpfname);
if (fd == -1) {
fprintf(stderr, "Error: cannot create .Xauthority file\n");
exit(1);
}
if (fchown(fd, getuid(), getgid()) == -1)
errExit("chown");
close(fd);
pid_t child = fork();
if (child < 0)
errExit("fork");
if (child == 0) {
drop_privs(1);
clearenv();
#ifdef HAVE_GCOV
__gcov_flush();
#endif
execlp("/usr/bin/xauth", "/usr/bin/xauth", "-v", "-f", tmpfname,
"generate", display, "MIT-MAGIC-COOKIE-1", "untrusted", NULL);
_exit(127);
}
// wait for the xauth process to finish
int status;
if (waitpid(child, &status, 0) != child)
errExit("waitpid");
if (WIFEXITED(status) && WEXITSTATUS(status) == 0) {
/* success */
}
else if (WIFEXITED(status)) {
fprintf(stderr, "Failed to create untrusted X cookie: xauth: exit %d\n",
WEXITSTATUS(status));
exit(1);
}
else if (WIFSIGNALED(status)) {
fprintf(stderr, "Failed to create untrusted X cookie: xauth: %s\n",
strsignal(WTERMSIG(status)));
exit(1);
}
else {
fprintf(stderr, "Failed to create untrusted X cookie: "
"xauth: un-decodable exit status %04x\n", status);
exit(1);
}
// ensure the file has the correct permissions and move it
// into the correct location.
if (stat(tmpfname, &s) == -1) {
fprintf(stderr, "Error: .Xauthority file was not created\n");
exit(1);
}
if (set_perms(tmpfname, getuid(), getgid(), 0600))
errExit("set_perms");
// move the temporary file in RUN_XAUTHORITY_SEC_FILE in order to have it deleted
// automatically when the sandbox is closed (rename doesn't work)
// root needed
if (copy_file(tmpfname, RUN_XAUTHORITY_SEC_FILE, getuid(), getgid(), 0600)) {
fprintf(stderr, "Error: cannot create the new .Xauthority file\n");
exit(1);
}
if (set_perms(RUN_XAUTHORITY_SEC_FILE, getuid(), getgid(), 0600))
errExit("set_perms");
/* coverity[toctou] */
unlink(tmpfname);
umount("/tmp");
// Ensure there is already a file in the usual location, so that bind-mount below will work.
// todo: fix TOCTOU races, currently managed by imposing /usr/bin/xauth as executable
char *dest;
if (asprintf(&dest, "%s/.Xauthority", cfg.homedir) == -1)
errExit("asprintf");
if (stat(dest, &s) == -1) {
// create an .Xauthority file
touch_file_as_user(dest, getuid(), getgid(), 0600);
}
if (is_link(dest)) {
fprintf(stderr, "Error: .Xauthority is a symbolic link\n");
exit(1);
}
// mount
if (mount(RUN_XAUTHORITY_SEC_FILE, dest, "none", MS_BIND, "mode=0600") == -1) {
fprintf(stderr, "Error: cannot mount the new .Xauthority file\n");
exit(1);
}
// just in case...
if (set_perms(dest, getuid(), getgid(), 0600))
errExit("set_perms");
free(dest);
#endif
}
void fs_x11(void) {
#ifdef HAVE_X11
int display = x11_display();
if (display <= 0)
return;
char *x11file;
if (asprintf(&x11file, "/tmp/.X11-unix/X%d", display) == -1)
errExit("asprintf");
struct stat x11stat;
if (stat(x11file, &x11stat) == -1 || !S_ISSOCK(x11stat.st_mode)) {
free(x11file);
return;
}
if (arg_debug || arg_debug_whitelists)
fprintf(stderr, "Masking all X11 sockets except %s\n", x11file);
// Move the real /tmp/.X11-unix to a scratch location
// so we can still access x11file after we mount a
// tmpfs over /tmp/.X11-unix.
int rv = mkdir(RUN_WHITELIST_X11_DIR, 0700);
if (rv == -1)
errExit("mkdir");
if (set_perms(RUN_WHITELIST_X11_DIR, 0, 0, 0700))
errExit("set_perms");
if (mount("/tmp/.X11-unix", RUN_WHITELIST_X11_DIR, 0, MS_BIND|MS_REC, 0) < 0)
errExit("mount bind");
// This directory must be mode 1777, or Xlib will barf.
if (mount("tmpfs", "/tmp/.X11-unix", "tmpfs",
MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_STRICTATIME | MS_REC,
"mode=1777,uid=0,gid=0") < 0)
errExit("mounting tmpfs on /tmp/.X11-unix");
fs_logger("tmpfs /tmp/.X11-unix");
// create an empty file which will have the desired socket bind-mounted over it
int fd = open(x11file, O_RDWR|O_CREAT|O_EXCL, x11stat.st_mode & ~S_IFMT);
if (fd < 0)
errExit(x11file);
if (fchown(fd, x11stat.st_uid, x11stat.st_gid))
errExit("fchown");
close(fd);
// do the mount
char *wx11file;
if (asprintf(&wx11file, "%s/X%d", RUN_WHITELIST_X11_DIR, display) == -1)
errExit("asprintf");
if (mount(wx11file, x11file, NULL, MS_BIND|MS_REC, NULL) < 0)
errExit("mount bind");
fs_logger2("whitelist", x11file);
free(x11file);
free(wx11file);
// block access to RUN_WHITELIST_X11_DIR
if (mount(RUN_RO_DIR, RUN_WHITELIST_X11_DIR, 0, MS_BIND, 0) < 0)
errExit("mount");
fs_logger2("blacklist", RUN_WHITELIST_X11_DIR);
#endif
}
void x11_block(void) {
#ifdef HAVE_X11
// check abstract socket presence and network namespace options
if ((!arg_nonetwork && !cfg.bridge0.configured && !cfg.interface0.configured)
&& x11_abstract_sockets_present()) {
fprintf(stderr, "ERROR: --x11=none specified, but abstract X11 socket still accessible.\n"
"Additional setup required. To block abstract X11 socket you can either:\n"
" * use network namespace in firejail (--net=none, --net=...)\n"
" * add \"-nolisten local\" to xserver options\n"
" (eg. to your display manager config, or /etc/X11/xinit/xserverrc)\n");
exit(1);
}
// blacklist sockets
profile_check_line("blacklist /tmp/.X11-unix", 0, NULL);
profile_add(strdup("blacklist /tmp/.X11-unix"));
// blacklist .Xauthority
profile_check_line("blacklist ${HOME}/.Xauthority", 0, NULL);
profile_add(strdup("blacklist ${HOME}/.Xauthority"));
char *xauthority = getenv("XAUTHORITY");
if (xauthority) {
char *line;
if (asprintf(&line, "blacklist %s", xauthority) == -1)
errExit("asprintf");
profile_check_line(line, 0, NULL);
profile_add(line);
}
// clear environment
env_store("DISPLAY", RMENV);
env_store("XAUTHORITY", RMENV);
#endif
}
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