privilege separated copy

examples/cp/.gitignore

@@ -0,0 +1 @@
+cp_priv_sep

examples/cp/Makefile

@@ -1,13 +1,17 @@
 C=clang
 
-all: c c_cgroup ml
+all: c cp_priv_sep c_cgroup ml
 
 clean:
-	rm -f c ml
+	rm -f c cp_priv_sep c_cgroup ml
 
 c: cp.c
 	${C} -o c cp.c
 
+cp_priv_sep: cp_priv_sep.c ../../lib/clone3.c ../../include/clone3.h
+	${C} -I../../include -o cp_priv_sep cp_priv_sep.c ../../lib/clone3.c
+	sudo setcap CAP_SYS_ADMIN+eip ./cp_priv_sep
+
 c_cgroup: cp_cgroup.c
 	${C} -o c_cgroup cp_cgroup.c
 

examples/cp/cp_priv_sep.c

@@ -0,0 +1,154 @@
+// For privilege separation
+#include <clone3.h>
+#include <fcntl.h>
+#include <linux/wait.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+// This program
+#include <stdio.h>
+
+#define BUF_SIZE 4096
+
+struct copy_args {
+  char *src;
+  char *dst;
+};
+
+int process_args(int argc, char **argv, struct copy_args *);
+int do_copy(struct copy_args *args);
+
+int main(int argc, char **argv) {
+  pid_t child;
+
+  // Spawn args processor
+  int args_pid_fd;
+
+  struct clone_args args_processor_cl_args = {
+      .flags = CLONE_NEWIPC | CLONE_NEWNET | CLONE_NEWNS | CLONE_NEWPID |
+               CLONE_NEWUSER | CLONE_NEWUTS | CLONE_PIDFD,
+      .pidfd = (uint64_t)&args_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,
+  };
+
+  int args_pipe_fds[2];
+  if (pipe(args_pipe_fds) < 0) {
+    perror("pipe");
+    exit(-1);
+  }
+
+  if ((child = clone3(&args_processor_cl_args)) == 0) {
+    char args[sizeof(struct copy_args)];
+
+    int code = process_args(argc, argv, &args);
+    if (code != 0) {
+      exit(code);
+    }
+
+    write(args_pipe_fds[1], &args, sizeof(args));
+    exit(0);
+  } else if (child < 0) {
+    perror("clone3");
+    return -1;
+  }
+
+  // Wait for args processor
+  // Implicit assertion that sizeof(args) < the pipe buffer size (won't block)
+  siginfo_t status;
+  if (waitid(P_PIDFD, args_pid_fd, &status, WEXITED) == -1) {
+    perror("waitid");
+    return -1;
+  }
+
+  if (status.si_status != 0) {
+    return status.si_status;
+  }
+
+  char args[sizeof(struct copy_args)];
+  read(args_pipe_fds[0], &args, sizeof(args));
+
+  // Spawn copier (can be more separated)
+  int copy_pid_fd;
+
+  struct clone_args do_copy_cl_args = {
+      .flags = CLONE_NEWIPC | CLONE_NEWNET | CLONE_NEWPID | CLONE_NEWUTS |
+               CLONE_PIDFD,
+      .pidfd = (uint64_t)&copy_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,
+  };
+
+  if ((child = clone3(&do_copy_cl_args)) == 0) {
+    int code = do_copy(&args);
+    exit(code);
+  } else if (child < 0) {
+    perror("clone3");
+    return -1;
+  }
+
+  if (waitid(P_PIDFD, copy_pid_fd, &status, WEXITED) == -1) {
+    perror("waitid");
+    return -1;
+  }
+
+  return status.si_status;
+}
+
+int process_args(int argc, char **argv, struct copy_args *args) {
+  if (argc != 3) {
+    fprintf(stderr, "usage: %s SRC DST\n", argv[0]);
+    return -1;
+  }
+
+  args->src = argv[1];
+  args->dst = argv[2];
+
+  return 0;
+}
+
+int do_copy(struct copy_args *args) {
+  fprintf(stderr, "src: `%s`; dst: `%s`\n", args->src, args->dst);
+  int src_fd, dst_fd;
+
+  if ((src_fd = open(args->src, O_RDONLY)) < 0) {
+    perror("open");
+    return 1;
+  }
+  if ((dst_fd = open(args->dst, O_WRONLY | O_CREAT | O_TRUNC)) < 0) {
+    perror("open");
+    return 1;
+  }
+
+  char buf[BUF_SIZE];
+  while (1) {
+    int read_bytes = read(src_fd, buf, BUF_SIZE);
+    if (read_bytes < 0) {
+      perror("read");
+      return read_bytes;
+    }
+
+    if (!read_bytes) {
+      fprintf(stderr, "copy complete\n");
+      return 0;
+    }
+
+    if (write(dst_fd, buf, read_bytes) < 0) {
+      perror("write");
+      return -1;
+    }
+  }
+
+  return 0;
+}