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/*
* Copyright (C) 2014-2018 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.
*/
#ifdef HAVE_SECCOMP
#include "firejail.h"
#include "../include/seccomp.h"
#include <sys/mman.h>
typedef struct filter_list {
struct filter_list *next;
struct sock_fprog prog;
const char *fname;
} FilterList;
static FilterList *filter_list_head = NULL;
static int err_printed = 0;
extern int enforce_seccomp;
char *seccomp_check_list(const char *str) {
assert(str);
if (strlen(str) == 0) {
fprintf(stderr, "Error: empty syscall lists are not allowed\n");
exit(1);
}
int len = strlen(str) + 1;
char *rv = malloc(len);
if (!rv)
errExit("malloc");
memset(rv, 0, len);
const char *ptr1 = str;
char *ptr2 = rv;
while (*ptr1 != '\0') {
if (isalnum(*ptr1) || *ptr1 == '_' || *ptr1 == ',' || *ptr1 == ':' || *ptr1 == '@' || *ptr1 == '-')
*ptr2++ = *ptr1++;
else {
fprintf(stderr, "Error: invalid syscall list\n");
exit(1);
}
}
return rv;
}
// install seccomp filters
int seccomp_install_filters(void) {
int r = 0;
FilterList *fl = filter_list_head;
if (fl) {
prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
for (; fl; fl = fl->next) {
assert(fl->fname);
if (arg_debug)
printf("Installing %s seccomp filter\n", fl->fname);
if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &fl->prog)) {
if (enforce_seccomp) {
fprintf(stderr, "Error: a seccomp-enabled Linux kernel is required, exiting...\n");
exit(1);
}
if (!err_printed)
fwarning("seccomp disabled, it requires a Linux kernel version 3.5 or newer.\n");
err_printed = 1;
r = 1;
}
}
}
return r;
}
int seccomp_load(const char *fname) {
assert(fname);
// open filter file
int fd = open(fname, O_RDONLY);
if (fd == -1)
goto errexit;
// calculate the number of entries
int size = lseek(fd, 0, SEEK_END);
if (size == -1)
goto errexit;
unsigned short entries = (unsigned short) size / (unsigned short) sizeof(struct sock_filter);
if (arg_debug)
printf("configuring %d seccomp entries in %s\n", entries, fname);
// read filter
struct sock_filter *filter = mmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
if (filter == MAP_FAILED)
goto errexit;
// close file
close(fd);
FilterList *fl = malloc(sizeof(FilterList));
if (!fl) {
fprintf(stderr, "Error: cannot allocate memory\n");
exit(1);
}
fl->next = filter_list_head;
fl->prog.len = entries;
fl->prog.filter = filter;
fl->fname = strdup(fname);
if (fl->fname == NULL)
errExit("strdup");
filter_list_head = fl;
if (arg_debug && access(PATH_FSEC_PRINT, X_OK) == 0) {
sbox_run(SBOX_USER | SBOX_CAPS_NONE | SBOX_SECCOMP, 2,
PATH_FSEC_PRINT, fname);
}
return 0;
errexit:
fprintf(stderr, "Error: cannot read %s\n", fname);
exit(1);
}
// 32 bit arch filter installed on 64 bit architectures
#if defined(__x86_64__)
#if defined(__LP64__)
static void seccomp_filter_32(void) {
if (seccomp_load(RUN_SECCOMP_32) == 0) {
if (arg_debug)
printf("Dual 32/64 bit seccomp filter configured\n");
}
}
#endif
#endif
static void seccomp_filter_block_secondary(void) {
if (seccomp_load(RUN_SECCOMP_BLOCK_SECONDARY) == 0) {
if (arg_debug)
printf("Secondary arch blocking seccomp filter configured\n");
}
}
// drop filter for seccomp option
int seccomp_filter_drop(void) {
// if we have multiple seccomp commands, only one of them is executed
// in the following order:
// - seccomp.drop list
// - seccomp list
// - seccomp
if (cfg.seccomp_list_drop == NULL) {
// default seccomp
if (cfg.seccomp_list == NULL) {
if (arg_seccomp_block_secondary)
seccomp_filter_block_secondary();
else {
#if defined(__x86_64__)
#if defined(__LP64__)
seccomp_filter_32();
#endif
#endif
}
}
// default seccomp filter with additional drop list
else { // cfg.seccomp_list != NULL
if (arg_seccomp_block_secondary)
seccomp_filter_block_secondary();
else {
#if defined(__x86_64__)
#if defined(__LP64__)
seccomp_filter_32();
#endif
#endif
}
if (arg_debug)
printf("Build default+drop seccomp filter\n");
// build the seccomp filter as a regular user
int rv;
if (arg_allow_debuggers)
rv = sbox_run(SBOX_USER | SBOX_CAPS_NONE | SBOX_SECCOMP, 7,
PATH_FSECCOMP, "default", "drop", RUN_SECCOMP_CFG, RUN_SECCOMP_POSTEXEC, cfg.seccomp_list, "allow-debuggers");
else
rv = sbox_run(SBOX_USER | SBOX_CAPS_NONE | SBOX_SECCOMP, 6,
PATH_FSECCOMP, "default", "drop", RUN_SECCOMP_CFG, RUN_SECCOMP_POSTEXEC, cfg.seccomp_list);
if (rv)
exit(rv);
// optimize the new filter
rv = sbox_run(SBOX_USER | SBOX_CAPS_NONE | SBOX_SECCOMP, 2, PATH_FSEC_OPTIMIZE, RUN_SECCOMP_CFG);
if (rv)
exit(rv);
}
}
// drop list without defaults - secondary filters are not installed
// except when secondary architectures are explicitly blocked
else { // cfg.seccomp_list_drop != NULL
if (arg_seccomp_block_secondary)
seccomp_filter_block_secondary();
if (arg_debug)
printf("Build drop seccomp filter\n");
// build the seccomp filter as a regular user
int rv;
if (arg_allow_debuggers)
rv = sbox_run(SBOX_USER | SBOX_CAPS_NONE | SBOX_SECCOMP, 6,
PATH_FSECCOMP, "drop", RUN_SECCOMP_CFG, RUN_SECCOMP_POSTEXEC, cfg.seccomp_list_drop, "allow-debuggers");
else
rv = sbox_run(SBOX_USER | SBOX_CAPS_NONE | SBOX_SECCOMP, 5,
PATH_FSECCOMP, "drop", RUN_SECCOMP_CFG, RUN_SECCOMP_POSTEXEC, cfg.seccomp_list_drop);
if (rv)
exit(rv);
// optimize the drop filter
rv = sbox_run(SBOX_USER | SBOX_CAPS_NONE | SBOX_SECCOMP, 2, PATH_FSEC_OPTIMIZE, RUN_SECCOMP_CFG);
if (rv)
exit(rv);
}
// load the filter
if (seccomp_load(RUN_SECCOMP_CFG) == 0) {
if (arg_debug)
printf("seccomp filter configured\n");
}
if (arg_debug && access(PATH_FSEC_PRINT, X_OK) == 0) {
struct stat st;
if (stat(RUN_SECCOMP_POSTEXEC, &st) != -1 && st.st_size != 0) {
printf("configuring postexec seccomp filter in %s\n", RUN_SECCOMP_POSTEXEC);
sbox_run(SBOX_USER | SBOX_CAPS_NONE | SBOX_SECCOMP, 2,
PATH_FSEC_PRINT, RUN_SECCOMP_POSTEXEC);
}
}
return 0;
}
// keep filter for seccomp option
int seccomp_filter_keep(void) {
// secondary filters are not installed except when secondary
// architectures are explicitly blocked
if (arg_seccomp_block_secondary)
seccomp_filter_block_secondary();
if (arg_debug)
printf("Build keep seccomp filter\n");
// build the seccomp filter as a regular user
int rv = sbox_run(SBOX_USER | SBOX_CAPS_NONE | SBOX_SECCOMP, 5,
PATH_FSECCOMP, "keep", RUN_SECCOMP_CFG, RUN_SECCOMP_POSTEXEC, cfg.seccomp_list_keep);
if (rv) {
fprintf(stderr, "Error: cannot configure seccomp filter\n");
exit(rv);
}
if (arg_debug)
printf("seccomp filter configured\n");
// load the filter
if (seccomp_load(RUN_SECCOMP_CFG) == 0) {
if (arg_debug)
printf("seccomp filter configured\n");
}
if (arg_debug && access(PATH_FSEC_PRINT, X_OK) == 0) {
struct stat st;
if (stat(RUN_SECCOMP_POSTEXEC, &st) != -1 && st.st_size != 0) {
printf("configuring postexec seccomp filter in %s\n", RUN_SECCOMP_POSTEXEC);
sbox_run(SBOX_USER | SBOX_CAPS_NONE | SBOX_SECCOMP, 2,
PATH_FSEC_PRINT, RUN_SECCOMP_POSTEXEC);
}
}
return 0;
}
void seccomp_print_filter(pid_t pid) {
EUID_ASSERT();
// 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;
}
}
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 denied.\n");
exit(1);
}
}
// find the seccomp filter
EUID_ROOT();
char *fname;
if (asprintf(&fname, "/proc/%d/root%s", pid, RUN_SECCOMP_CFG) == -1)
errExit("asprintf");
struct stat s;
if (stat(fname, &s) == -1) {
printf("Cannot access seccomp filter.\n");
exit(1);
}
// read and print the filter - run this as root, the user doesn't have access
sbox_run(SBOX_ROOT | SBOX_SECCOMP, 2, PATH_FSEC_PRINT, fname);
free(fname);
exit(0);
}
#endif // HAVE_SECCOMP
|