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#define _GNU_SOURCE
#include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <grp.h>
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <termios.h>
#include <errno.h>
#include <unistd.h>
/* Open Source projects like conda-forge, want to package podman and are based
off of centos:6, Conda-force has minimal libc requirements and is lacking
the memfd.h file, so we use mmam.h
*/
#ifndef MFD_ALLOW_SEALING
#define MFD_ALLOW_SEALING 2U
#endif
#ifndef MFD_CLOEXEC
#define MFD_CLOEXEC 1U
#endif
#ifndef F_LINUX_SPECIFIC_BASE
#define F_LINUX_SPECIFIC_BASE 1024
#endif
#ifndef F_ADD_SEALS
#define F_ADD_SEALS (F_LINUX_SPECIFIC_BASE + 9)
#define F_GET_SEALS (F_LINUX_SPECIFIC_BASE + 10)
#endif
#ifndef F_SEAL_SEAL
#define F_SEAL_SEAL 0x0001LU
#endif
#ifndef F_SEAL_SHRINK
#define F_SEAL_SHRINK 0x0002LU
#endif
#ifndef F_SEAL_GROW
#define F_SEAL_GROW 0x0004LU
#endif
#ifndef F_SEAL_WRITE
#define F_SEAL_WRITE 0x0008LU
#endif
#define BUFSTEP 1024
static const char *_max_user_namespaces = "/proc/sys/user/max_user_namespaces";
static const char *_unprivileged_user_namespaces = "/proc/sys/kernel/unprivileged_userns_clone";
static int _containers_unshare_parse_envint(const char *envname) {
char *p, *q;
long l;
p = getenv(envname);
if (p == NULL) {
return -1;
}
q = NULL;
l = strtol(p, &q, 10);
if ((q == NULL) || (*q != '\0')) {
fprintf(stderr, "Error parsing \"%s\"=\"%s\"!\n", envname, p);
_exit(1);
}
unsetenv(envname);
return l;
}
static void _check_proc_sys_file(const char *path)
{
FILE *fp;
char buf[32];
size_t n_read;
long r;
fp = fopen(path, "r");
if (fp == NULL) {
if (errno != ENOENT)
fprintf(stderr, "Error reading %s: %m\n", _max_user_namespaces);
} else {
memset(buf, 0, sizeof(buf));
n_read = fread(buf, 1, sizeof(buf) - 1, fp);
if (n_read > 0) {
r = atoi(buf);
if (r == 0) {
fprintf(stderr, "User namespaces are not enabled in %s.\n", path);
}
} else {
fprintf(stderr, "Error reading %s: no contents, should contain a number greater than 0.\n", path);
}
fclose(fp);
}
}
static char **parse_proc_stringlist(const char *list) {
int fd, n, i, n_strings;
char *buf, *new_buf, **ret;
size_t size, new_size, used;
fd = open(list, O_RDONLY);
if (fd == -1) {
return NULL;
}
buf = NULL;
size = 0;
used = 0;
for (;;) {
new_size = used + BUFSTEP;
new_buf = realloc(buf, new_size);
if (new_buf == NULL) {
free(buf);
fprintf(stderr, "realloc(%ld): out of memory\n", (long)(size + BUFSTEP));
return NULL;
}
buf = new_buf;
size = new_size;
memset(buf + used, '\0', size - used);
n = read(fd, buf + used, size - used - 1);
if (n < 0) {
fprintf(stderr, "read(): %m\n");
return NULL;
}
if (n == 0) {
break;
}
used += n;
}
close(fd);
n_strings = 0;
for (n = 0; n < used; n++) {
if ((n == 0) || (buf[n-1] == '\0')) {
n_strings++;
}
}
ret = calloc(n_strings + 1, sizeof(char *));
if (ret == NULL) {
fprintf(stderr, "calloc(): out of memory\n");
return NULL;
}
i = 0;
for (n = 0; n < used; n++) {
if ((n == 0) || (buf[n-1] == '\0')) {
ret[i++] = &buf[n];
}
}
ret[i] = NULL;
return ret;
}
static int containers_reexec(void) {
char **argv, *exename;
int fd, mmfd, n_read, n_written;
struct stat st;
char buf[2048];
argv = parse_proc_stringlist("/proc/self/cmdline");
if (argv == NULL) {
return -1;
}
fd = open("/proc/self/exe", O_RDONLY | O_CLOEXEC);
if (fd == -1) {
fprintf(stderr, "open(\"/proc/self/exe\"): %m\n");
return -1;
}
if (fstat(fd, &st) == -1) {
fprintf(stderr, "fstat(\"/proc/self/exe\"): %m\n");
return -1;
}
exename = basename(argv[0]);
mmfd = syscall(SYS_memfd_create, exename, (long) MFD_ALLOW_SEALING | MFD_CLOEXEC);
if (mmfd == -1) {
fprintf(stderr, "memfd_create(): %m\n");
return -1;
}
for (;;) {
n_read = read(fd, buf, sizeof(buf));
if (n_read < 0) {
fprintf(stderr, "read(\"/proc/self/exe\"): %m\n");
return -1;
}
if (n_read == 0) {
break;
}
n_written = write(mmfd, buf, n_read);
if (n_written < 0) {
fprintf(stderr, "write(anonfd): %m\n");
return -1;
}
if (n_written != n_read) {
fprintf(stderr, "write(anonfd): short write (%d != %d)\n", n_written, n_read);
return -1;
}
}
close(fd);
if (fcntl(mmfd, F_ADD_SEALS, F_SEAL_SHRINK | F_SEAL_GROW | F_SEAL_WRITE | F_SEAL_SEAL) == -1) {
close(mmfd);
fprintf(stderr, "Error sealing memfd copy: %m\n");
return -1;
}
if (fexecve(mmfd, argv, environ) == -1) {
close(mmfd);
fprintf(stderr, "Error during reexec(...): %m\n");
return -1;
}
return 0;
}
void _containers_unshare(void)
{
int flags, pidfd, continuefd, n, pgrp, sid, ctty;
char buf[2048];
flags = _containers_unshare_parse_envint("_Containers-unshare");
if (flags == -1) {
return;
}
if ((flags & CLONE_NEWUSER) != 0) {
if (unshare(CLONE_NEWUSER) == -1) {
fprintf(stderr, "Error during unshare(CLONE_NEWUSER): %m\n");
_check_proc_sys_file (_max_user_namespaces);
_check_proc_sys_file (_unprivileged_user_namespaces);
_exit(1);
}
}
pidfd = _containers_unshare_parse_envint("_Containers-pid-pipe");
if (pidfd != -1) {
snprintf(buf, sizeof(buf), "%llu", (unsigned long long) getpid());
size_t size = write(pidfd, buf, strlen(buf));
if (size != strlen(buf)) {
fprintf(stderr, "Error writing PID to pipe on fd %d: %m\n", pidfd);
_exit(1);
}
close(pidfd);
}
continuefd = _containers_unshare_parse_envint("_Containers-continue-pipe");
if (continuefd != -1) {
n = read(continuefd, buf, sizeof(buf));
if (n > 0) {
fprintf(stderr, "Error: %.*s\n", n, buf);
_exit(1);
}
close(continuefd);
}
sid = _containers_unshare_parse_envint("_Containers-setsid");
if (sid == 1) {
if (setsid() == -1) {
fprintf(stderr, "Error during setsid: %m\n");
_exit(1);
}
}
pgrp = _containers_unshare_parse_envint("_Containers-setpgrp");
if (pgrp == 1) {
if (setpgrp() == -1) {
fprintf(stderr, "Error during setpgrp: %m\n");
_exit(1);
}
}
ctty = _containers_unshare_parse_envint("_Containers-ctty");
if (ctty != -1) {
if (ioctl(ctty, TIOCSCTTY, 0) == -1) {
fprintf(stderr, "Error while setting controlling terminal to %d: %m\n", ctty);
_exit(1);
}
}
if ((flags & CLONE_NEWUSER) != 0) {
if (setresgid(0, 0, 0) != 0) {
fprintf(stderr, "Error during setresgid(0): %m\n");
_exit(1);
}
if (setresuid(0, 0, 0) != 0) {
fprintf(stderr, "Error during setresuid(0): %m\n");
_exit(1);
}
}
if ((flags & ~CLONE_NEWUSER) != 0) {
if (unshare(flags & ~CLONE_NEWUSER) == -1) {
fprintf(stderr, "Error during unshare(...): %m\n");
_exit(1);
}
}
if (containers_reexec() != 0) {
_exit(1);
}
return;
}
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