privilege separated fib function

examples/fib/.gitignore

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+fib_priv_sep

examples/fib/Makefile

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+C=clang -Wall
+
+all: fib_priv_sep
+
+clean:
+	rm -f fib_priv_sep
+
+fib_priv_sep: fib_priv_sep.c ../../lib/clone3.c ../../include/clone3.h
+	${C} -I../../include -o fib_priv_sep fib_priv_sep.c ../../lib/clone3.c
+	sudo setcap CAP_SYS_ADMIN+eip ./fib_priv_sep

examples/fib/fib_priv_sep.c

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+// For privilege separation
+#include <clone3.h>
+
+#include <linux/wait.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+
+// This program
+#include <stdint.h>
+#include <stdio.h>
+
+uint64_t fib(uint64_t i) {
+  uint64_t a = 0;
+  uint64_t b = 1;
+
+  for (; i > 0; i--) {
+    uint64_t old_b = b;
+    b = b + a;
+    a = old_b;
+  }
+
+  return a;
+}
+
+int real_main(int argc, char **argv);
+
+int main(int argc, char **argv) {
+  int pid_fd;
+
+  struct clone_args cl_args = {
+      .flags = CLONE_NEWIPC | CLONE_NEWNET | CLONE_NEWNS | CLONE_NEWPID |
+               CLONE_NEWUSER | CLONE_NEWUTS | CLONE_PIDFD,
+      .pidfd = (uint64_t)&pid_fd,
+      .child_tid = (uint64_t)NULL,
+      .parent_tid = (uint64_t)NULL,
+      .exit_signal = SIGCHLD,
+      .stack = (uint64_t)NULL,
+      .stack_size = 0,
+      .tls = (uint64_t)NULL,
+  };
+
+  pid_t child = clone3(&cl_args);
+  if (child < 0) {
+    perror("clone3");
+    exit(-1);
+  } else if (child == 0) {
+    int code = real_main(argc, argv);
+    exit(code);
+  } else {
+    siginfo_t status;
+    if (waitid(P_PIDFD, pid_fd, &status, WEXITED) == -1) {
+      perror("waitid");
+      return -1;
+    }
+
+    exit(status.si_status);
+  }
+}
+
+int real_main(int argc, char **argv) {
+  if (argc != 2) {
+    fprintf(stderr, "expected 1 argument\n");
+    return -1;
+  }
+
+  uint64_t i = 0;
+  if (sscanf(argv[1], "%lu", &i) != 1) {
+    fprintf(stderr, "sscanf failed\n");
+    return -1;
+  }
+
+  uint64_t fib_result = fib(i);
+  printf("fib(%lu) = %lu\n", i, fib_result);
+  return 0;
+}

include/clone3.h

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+#include <linux/sched.h>
+
+long clone3(struct clone_args *cl_args);

lib/clone3.c

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+#include <clone3.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+long clone3(struct clone_args *cl_args) {
+  return syscall(SYS_clone3, cl_args, sizeof(struct clone_args));
+}