Add small unprivileged chroot

sysa/after_wrap.kaem

@@ -0,0 +1,10 @@
+#!/bin/sh
+
+PATH=./${ARCH_DIR}/bin
+
+./${ARCH_DIR}/bin/M2-Mesoplanet --architecture ${ARCH} \
+  -f sysa/wrap.c \
+  -o ./${ARCH_DIR}/bin/wrap \
+  --temp-directory ./x86/artifact
+
+exec ./${ARCH_DIR}/bin/wrap ./${ARCH_DIR}/bin/kaem --verbose --strict --file sysa/after.kaem

sysa/wrap.c

@@ -0,0 +1,116 @@
+#define CLONE_NEWUSER 0x10000000
+#define CLONE_NEWNS 0x00020000
+#define MS_BIND 4096
+
+#include <stdio.h>
+#include <string.h>
+#include <bootstrappable.h>
+
+#include <sys/stat.h>
+
+int unshare(int flags) {
+  asm (
+    "lea_ebx,[esp+DWORD] %4"
+    "mov_ebx,[ebx]"
+    "mov_eax, %310"
+    "int !0x80"
+  );
+}
+
+int geteuid() {
+  asm (
+    "mov_eax, %201"
+    "int !0x80"
+  );
+}
+
+int getegid() {
+  asm (
+    "mov_eax, %202"
+    "int !0x80"
+  );
+}
+
+int mount(
+  char *source, char *target, char *filesystemtype,
+  unsigned mountflags, void *data
+) {
+  asm (
+    "DEFINE mov_esi,[esp+DWORD] 8BB424"
+    "DEFINE mov_edi,[esp+DWORD] 8BBC24"
+    "lea_ebx,[esp+DWORD] %20"
+    "mov_ebx,[ebx]"
+    "lea_ecx,[esp+DWORD] %16"
+    "mov_ecx,[ecx]"
+    "lea_edx,[esp+DWORD] %12"
+    "mov_edx,[edx]"
+    "mov_esi,[esp+DWORD] %8 ; mov esi, [esp+8]"
+    "mov_edi,[esp+DWORD] %4 ; mov edi, [esp+4]"
+    "mov_eax, %21"
+    "int !0x80"
+  );
+}
+
+int chroot(char *path) {
+  asm (
+    "lea_ebx,[esp+DWORD] %4"
+    "mov_ebx,[ebx]"
+    "mov_eax, %61"
+    "int !0x80"
+  );
+}
+
+int set_map(int parent_id, char *path) {
+  char *map_contents;
+  char *parent_id_str;
+  int fd = open(path, O_WRONLY, 0);
+  require(fd != -1, "Cannot open map file");
+
+  map_contents = calloc(37, sizeof(char));
+
+  strcpy(map_contents, "0 ");
+  parent_id_str = int2str(parent_id, 10, 0);
+  strcat(map_contents, parent_id_str);
+  strcat(map_contents, " 1");
+  write(fd, map_contents, strlen(map_contents));
+  write(STDOUT_FILENO, map_contents, strlen(map_contents));
+  free(map_contents);
+  close(fd);
+}
+
+void touch(char *path) {
+  int fd = open(path, O_CREAT, 0777);
+  require(fd != -1, "Cannot open file");
+  close(fd);
+}
+
+void deny_setgroups() {
+  int fd = open("/proc/self/setgroups", O_WRONLY, 0777);
+  require(fd != -1, "Failed to open /proc/self/setgroups");
+  write(fd, "deny", 4);
+  close(fd);
+}
+
+int main(int argc, char **argv, char **envp) {
+  int uid = geteuid();
+  int gid = getegid();
+  unshare(CLONE_NEWUSER | CLONE_NEWNS);
+  mkdir ("dev", 0755);
+  touch ("dev/null");
+  mount ("/dev/null", "dev/null", "", MS_BIND, NULL);
+  touch ("dev/zero");
+  mount ("/dev/zero", "dev/zero", "", MS_BIND, NULL);
+  touch ("dev/random");
+  mount ("/dev/random", "dev/random", "", MS_BIND, NULL);
+  touch ("dev/urandom");
+  mount ("/dev/urandom", "dev/urandom", "", MS_BIND, NULL);
+  touch ("dev/ptmx");
+  mount ("/dev/ptmx", "dev/ptmx", "", MS_BIND, NULL);
+  touch ("dev/tty");
+  mount ("/dev/tty", "dev/tty", "", MS_BIND, NULL);
+  deny_setgroups();
+  set_map(uid, "/proc/self/uid_map");
+  set_map(gid, "/proc/self/gid_map");
+  chroot (".");
+  execve (argv[1], argv + 4 , envp);
+}