1 files changed, 98 insertions, 0 deletions
diff --git a/git-protection.c b/git-protection.c
new file mode 100644
index 0000000..6084c74
--- /dev/null
+++ b/git-protection.c
@@ -0,0 +1,98 @@
+/* See LICENSE file for copyright and license details. */
+#include <sys/mount.h>
+#include <sched.h>
+#include <libsimple.h>
+#include <libsimple-arg.h>
+
+NUSAGE(125, "utility [argument] ...");
+
+
+int
+main(int argc, char *argv[])
+{
+	int fds[2], status;
+	pid_t pid;
+	char *dir = NULL;
+	size_t dirsize = 0;
+	size_t dirlen = 0;
+	ssize_t r;
+
+	libsimple_default_failure_exit = 125;
+
+	ARGBEGIN {
+	default:
+		usage();
+	} ARGEND;
+
+	if (!argc)
+		usage();
+
+	if (unshare(CLONE_NEWNS))
+		eprintf("unshare CLONE_NEWNS:");
+	if (mount("none", "/", NULL, MS_REC | MS_SLAVE, NULL))
+		eprintf("mount none / NULL MS_REC|MS_SLAVE NULL:");
+
+	if (pipe(fds))
+		eprintf("pipe:");
+	pid = fork();
+	if (pid < 0)
+		eprintf("fork:");
+	if (pid == 0) {
+		if (setegid(getgid()))
+			eprintf("setegid <real group>:");
+		if (seteuid(getuid()))
+			eprintf("seteuid <real user>:");
+
+		close(fds[0]);
+		if (fds[1] != STDOUT_FILENO) {
+			if (dup2(fds[1], STDOUT_FILENO) != STDOUT_FILENO)
+				eprintf("dup2 <pipe> STDOUT_FILENO:");
+			close(fds[1]);
+		}
+		execlp(GIT_PATH, "git", "rev-parse", "--show-toplevel", NULL);
+		eprintf("execlp %s:", GIT_PATH);
+	}
+	close(fds[1]);
+	for (;;) {
+		if (dirlen == dirsize)
+			dir = erealloc(dir, dirsize += 512u);
+		r = read(fds[0], &dir[dirlen], dirsize - dirlen);
+		if (r <= 0) {
+			if (!r)
+				break;
+			if (errno == EINTR)
+				continue;
+			eprintf("read <pipe>:");
+		}
+		dirlen += (size_t)r;
+		if (!dirlen || dir[--dirlen] != '\n')
+			eprintf("received invalid output from `git rev-parse --show-toplevel`");
+	}
+	close(fds[0]);
+	if (waitpid(pid, &status, 0) != pid)
+		eprintf("waitpid <subprocess>:");
+	if (status) {
+		if (WIFSIGNALED(status))
+			eprintf("subprocess git was killed by signal %i\n", WTERMSIG(status));
+		exit(libsimple_default_failure_exit);
+	}
+	if (dirsize - dirlen < sizeof("/.git"))
+		dir = erealloc(dir, dirlen + sizeof("/.git"));
+	stpcpy(&dir[dirlen], "/.git");
+
+	if (mount(dir, dir, NULL, MS_BIND, NULL))
+		eprintf("mount %s %s NULL MS_BIND NULL:", dir, dir);
+	if (mount("none", dir, NULL, MS_BIND | MS_REMOUNT | MS_RDONLY, NULL))
+		eprintf("mount none %s NULL MS_BIND|MS_REMOUNT|MS_RDONLY NULL:", dir);
+
+	free(dir);
+
+	if (setegid(getgid()))
+		eprintf("setegid <real group>:");
+	if (seteuid(getuid()))
+		eprintf("seteuid <real user>:");
+
+	execvp(argv[0], argv);
+	enprintf(errno == ENOENT ? 127 : 126, "execvp %s:", argv[0]);
+	return 0;
+}