1 files changed, 195 insertions, 0 deletions
diff --git a/lib/libintercept.c b/lib/libintercept.c
new file mode 100644
index 0000000..8503308
--- /dev/null
+++ b/lib/libintercept.c
@@ -0,0 +1,195 @@
+#define _GNU_SOURCE  // RTLD_NEXT
+#include <stdio.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <stdarg.h>
+#include <string.h>
+#include <limits.h>
+#include <unistd.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <dlfcn.h>
+#include <spawn.h>  // posix_spawn
+#include <sys/socket.h>
+#include <sys/un.h>
+#include "libintercept.h"
+
+
+// Returns whether successful
+static bool sendall(int sock, const char *buffer, size_t length) {
+	size_t cursor = 0;
+	while (cursor < length) {
+		ssize_t nw = send(sock, buffer + cursor, length - cursor, 0);
+		if (nw <= 0) return false;
+		cursor += nw;
+	}
+	return true;
+}
+
+static void try_transmit_invocation(const char *pathname, char *const argv[]) {
+	fprintf(stderr, "try_transmit_invocation: %s ...\n", pathname);
+
+	const char *socketpath = getenv(COMM_SOCKET_ENVVAR);
+	if (socketpath == NULL) {
+		fprintf(stderr, "  socket path not given\n");
+		return;
+	}
+
+	// The SOCK_CLOEXEC option is technically unnecessary, but let's be careful.
+	int sock = socket(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0);
+	if (sock < 0) {
+		fprintf(stderr, "  cannot create socket: %s\n", strerror(errno));
+		return;
+	}
+
+	struct sockaddr_un addr;
+	memset(&addr, 0, sizeof addr);
+	addr.sun_family = AF_UNIX;
+	strncpy(addr.sun_path, socketpath, sizeof(addr.sun_path) - 1);
+
+	int ret = connect(sock, (const struct sockaddr*)&addr, sizeof addr);
+	if (ret < 0) {
+		fprintf(stderr, "  cannot connect to socket\n");
+		return;
+	}
+
+	size_t nargs = 0;
+	while (argv[nargs] != NULL) nargs++;
+
+	bool ok = false;
+	if (!sendall(sock, (const char*)&nargs, 8)) goto cleanup;
+	if (!sendall(sock, pathname, strlen(pathname) + 1)) goto cleanup;
+	for (size_t i = 0; i < nargs; i++) {
+		if (!sendall(sock, argv[i], strlen(argv[i]) + 1)) goto cleanup;
+	}
+
+	ok = true;
+
+cleanup:
+	if (!ok) fprintf(stderr, "  failed to write to socket\n");
+	close(sock);
+}
+
+__attribute__((constructor))
+static void constructor(void) {
+	fprintf(stderr, "constructor...\n");
+}
+
+// Abridged from glibc posix/execl.c, LGPL copyright FSF
+int execl(const char *pathname, const char *arg, ...) {
+	size_t argc;
+	va_list ap;
+	va_start(ap, arg);
+	for (argc = 1; va_arg(ap, const char*) && argc < INT_MAX; argc++) {}
+	va_end(ap);
+	if (argc >= INT_MAX) {
+		errno = E2BIG;
+		return -1;
+	}
+
+	char *argv[argc + 1];
+	argv[0] = (char*)arg;
+	va_start(ap, arg);
+	for (size_t i = 1; i < argc; i++) argv[i] = va_arg(ap, char*);
+	argv[argc] = NULL;
+	va_end(ap);
+
+	try_transmit_invocation(pathname, argv);
+
+	int (*real_execv)(const char*, char *const[]) = dlsym(RTLD_NEXT, "execv");
+	return real_execv(pathname, argv);
+}
+
+int execlp(const char *file, const char *arg, ...) {
+	size_t argc;
+	va_list ap;
+	va_start(ap, arg);
+	for (argc = 1; va_arg(ap, const char*) && argc < INT_MAX; argc++) {}
+	va_end(ap);
+	if (argc >= INT_MAX) {
+		errno = E2BIG;
+		return -1;
+	}
+
+	char *argv[argc + 1];
+	argv[0] = (char*)arg;
+	va_start(ap, arg);
+	for (size_t i = 1; i < argc; i++) argv[i] = va_arg(ap, char*);
+	argv[argc] = NULL;
+	va_end(ap);
+
+	try_transmit_invocation(file, argv);
+
+	int (*real_execvp)(const char*, char *const[]) = dlsym(RTLD_NEXT, "execvp");
+	return real_execvp(file, argv);
+}
+
+int execle(const char *pathname, const char *arg, ...) {
+	size_t argc;
+	va_list ap;
+	va_start(ap, arg);
+	for (argc = 1; va_arg(ap, const char*) && argc < INT_MAX; argc++) {}
+	char *const *envp = va_arg(ap, char *const *);
+	va_end(ap);
+	if (argc >= INT_MAX) {
+		errno = E2BIG;
+		return -1;
+	}
+
+	char *argv[argc + 1];
+	argv[0] = (char*)arg;
+	va_start(ap, arg);
+	for (size_t i = 1; i < argc; i++) argv[i] = va_arg(ap, char*);
+	argv[argc] = NULL;
+	va_end(ap);
+
+	try_transmit_invocation(pathname, argv);
+
+	int (*real_execvpe)(const char*, char *const[], char *const[]) = dlsym(RTLD_NEXT, "execvpe");
+	return real_execvpe(pathname, argv, envp);
+}
+
+int execv(const char *pathname, char *const argv[]) {
+	try_transmit_invocation(pathname, argv);
+
+	int (*real_execv)(const char*, char *const[]) = dlsym(RTLD_NEXT, "execv");
+	return real_execv(pathname, argv);
+}
+
+int execvp(const char *file, char *const argv[]) {
+	try_transmit_invocation(file, argv);
+
+	int (*real_execvp)(const char*, char *const[]) = dlsym(RTLD_NEXT, "execvp");
+	return real_execvp(file, argv);
+}
+
+int execve(const char *pathname, char *const argv[], char *const envp[]) {
+	try_transmit_invocation(pathname, argv);
+
+	int (*real_execve)(const char*, char *const[], char *const[]) = dlsym(RTLD_NEXT, "execve");
+	return real_execve(pathname, argv, envp);
+}
+
+int execvpe(const char *file, char *const argv[], char *const envp[]) {
+	try_transmit_invocation(file, argv);
+
+	int (*real_execvpe)(const char*, char *const[], char *const[]) = dlsym(RTLD_NEXT, "execvpe");
+	return real_execvpe(file, argv, envp);
+}
+
+int posix_spawn(
+	pid_t *pid, const char *path,
+	const posix_spawn_file_actions_t *file_actions,
+	const posix_spawnattr_t *attrp,
+	char *const argv[], char *const envp[]
+) {
+	try_transmit_invocation(path, argv);
+
+	int (*real_posix_spawn)(
+		pid_t*, const char*,
+		const posix_spawn_file_actions_t*,
+		const posix_spawnattr_t*,
+		char *const[], char *const[]
+	) = dlsym(RTLD_NEXT, "posix_spawn");
+	return real_posix_spawn(pid, path, file_actions, attrp, argv, envp);
+}