From 8798317ddc1bfbbdb3af56466a90a4fa61fb5309 Mon Sep 17 00:00:00 2001
From: Jake Hillion <jake@hillion.co.uk>
Date: Mon, 23 May 2022 00:28:16 +0100
Subject: [PATCH] wip: more examples

---
 examples/dir_descriptor.c       | 23 ++++++++++++++++++
 examples/unshare_mount_passwd.c | 42 +++++++++++++++++++++++++++++++++
 examples/unshare_user.c         | 20 ++++++++++++++++
 3 files changed, 85 insertions(+)
 create mode 100644 examples/dir_descriptor.c
 create mode 100644 examples/unshare_mount_passwd.c
 create mode 100644 examples/unshare_user.c

diff --git a/examples/dir_descriptor.c b/examples/dir_descriptor.c
new file mode 100644
index 0000000..18eaf2b
--- /dev/null
+++ b/examples/dir_descriptor.c
@@ -0,0 +1,23 @@
+#include <fcntl.h>
+#include <linux/types.h>
+#include <stdio.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+int main() {
+  int dirfd;
+
+  if ((dirfd = open("/tmp", __O_DIRECTORY)) < 0)
+    perror("opendir");
+  if (openat(dirfd, "filethatdoesexist", O_RDONLY) < 0)
+    perror("openat0");
+  if (chroot("/tmp"))
+    perror("chroot");
+  if (open("/etc/passwd", O_RDONLY) < 0)
+    perror("open");
+  if (openat(dirfd, "../etc/passwd", O_RDONLY) < 0)
+    perror("openat1");
+  if (openat(dirfd, "filethatdoesexist", O_RDONLY) < 0)
+    perror("openat2");
+}
+
diff --git a/examples/unshare_mount_passwd.c b/examples/unshare_mount_passwd.c
new file mode 100644
index 0000000..957fc84
--- /dev/null
+++ b/examples/unshare_mount_passwd.c
@@ -0,0 +1,42 @@
+#define _GNU_SOURCE
+#include <sched.h>
+#include <stdio.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#define BUF_SIZE 1024
+
+void print_file(int fd);
+
+int main() {
+	int fd;
+	
+	if ((fd = open("/etc/passwd", O_RDONLY)) < 0)
+		perror("open");
+	print_file(fd);
+	if (close(fd))
+		perror("close");
+	
+	if (unshare(CLONE_NEWNS))
+		perror("unshare");
+	printf("----- unshared -----\n");
+	
+	if ((fd = open("/etc/passwd", O_RDONLY)) < 0)
+		perror("open");
+	print_file(fd);
+	if (close(fd))
+		perror("close");
+}
+
+void print_file(int fd) {
+	char buf[BUF_SIZE];
+	int bytes_read;
+
+	while ((bytes_read = read(fd, buf, BUF_SIZE)) > 0)
+		if (write(1, buf, bytes_read) < 0)
+			perror("write");
+
+	if (bytes_read == -1)
+		perror("read");
+}
+
diff --git a/examples/unshare_user.c b/examples/unshare_user.c
new file mode 100644
index 0000000..f3254da
--- /dev/null
+++ b/examples/unshare_user.c
@@ -0,0 +1,20 @@
+#define _GNU_SOURCE
+#include <sched.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <fcntl.h>
+
+int main() {
+
+	int fd;
+
+	if (unshare(CLONE_NEWUSER))
+		perror("unshare");
+	if ((fd = open("/proc/self/uid_map", O_WRONLY)) == -1)
+		perror("open");	
+	if (write(fd, "0 0 4294967295\n", 15) == -1)
+		perror("write");
+	if (execl("/bin/bash", "/bin/bash", NULL))
+		perror("execl");
+}
+