implement a way for programs in the mount namespace (with glibc binaries) to launch processes in the original namespace (with musl binaries)

1 files changed, 96 insertions, 0 deletions

diff --git a/testserver.c b/testserver.c
new file mode 100644
index 0000000..091d580
--- /dev/null
+++ b/testserver.c
@@ -0,0 +1,96 @@
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <string.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <errno.h>
+#include <signal.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <sys/prctl.h>
+#include "utils.h"
+
+#define ERROR(f_, ...) fprintf(stderr, (f_), ##__VA_ARGS__)
+#define UNUSED(x)      (void)(x)
+#define ERROR_EXIT(f_, ...) { \
+		fprintf(stderr, (f_), ##__VA_ARGS__); \
+		return 1; \
+	}
+
+volatile sig_atomic_t term_caught = 0;
+void onterm(int sig)
+{
+	printf("sigterm caught\n");
+	UNUSED(sig);
+	term_caught = 1;
+}
+
+int main()
+{
+	int result;
+	int sock_fd, sock_conn;
+	int nsfd;
+
+	/* Get current namespace's file descriptor. */
+	nsfd = open("/proc/self/ns/mnt", O_RDONLY);
+	if (nsfd == -1)
+		ERROR_EXIT("error: failed to acquire mount namespace's fd.%s\n",
+				   strerror(errno));
+
+	/* Fork. */
+	pid_t ppid_before_fork = getpid();
+	pid_t pid = fork();
+	if (pid == -1)
+		ERROR_EXIT("fork: %s\n", strerror(errno));
+
+	if (pid == 0) {
+		/* Catch SIGTERM. */
+		struct sigaction sa = {0};
+		sa.sa_handler = onterm;
+		sigaction(SIGTERM, &sa, NULL);
+
+        /* Ignore SIGINT. */
+        signal(SIGINT, SIG_IGN);
+
+		/* Set the child to die when parent thread dies. */
+		int r = prctl(PR_SET_PDEATHSIG, SIGTERM);
+		if (r == -1)
+			ERROR_EXIT("prctl: %s\n", strerror(errno));
+		if (getppid() != ppid_before_fork)
+			ERROR_EXIT("error: parent has died already.\n");
+
+		/* Create unix socket. */
+		sock_fd = socket(AF_UNIX, SOCK_STREAM, 0);
+		if (sock_fd == -1)
+			ERROR_EXIT("socket: %s.\n", strerror(errno));
+
+		struct sockaddr_un sock_addr = {0};
+		sock_addr.sun_family = AF_UNIX;
+		strcpy(&sock_addr.sun_path[1], "/tmp/voidnsrun-test.sock");
+
+		if (bind(sock_fd, (struct sockaddr *)&sock_addr, sizeof(sock_addr)) == -1)
+			ERROR_EXIT("bind: %s\n", strerror(errno));
+
+		listen(sock_fd, 1);
+
+		while (!term_caught) {
+			sock_conn = accept(sock_fd, NULL, 0);
+			if (sock_conn == -1) {
+				ERROR("accept: %s\n", strerror(errno));
+				continue;
+			}
+			printf("accepted\n");
+			send_fd(sock_conn, nsfd);
+		}
+		printf("exiting\n");
+	} else {
+		/* This is parent. Launch a program. */
+		char *argv[2] = {"/bin/sh", NULL};
+
+		result = execvp(argv[0], (char *const *)argv);
+		if (result == -1)
+			ERROR_EXIT("execvp: %s\n", strerror(errno));
+	}
+
+	return 0;
+}
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