rexec: remove needless /proc/cmdline parsing

src/lxc/rexec.c

@@ -25,6 +25,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
 
 #include "config.h"
 #include "file_utils.h"
@@ -39,58 +40,6 @@
 #define LXC_MEMFD_REXEC_SEALS \
 	(F_SEAL_SEAL | F_SEAL_SHRINK | F_SEAL_GROW | F_SEAL_WRITE)
 
-static int push_vargs(char *data, int data_length, char ***output)
-{
-	int num = 0;
-	char *cur = data;
-
-	if (!data || *output)
-		return -1;
-
-	*output = must_realloc(NULL, sizeof(**output));
-
-	while (cur < data + data_length) {
-		num++;
-		*output = must_realloc(*output, (num + 1) * sizeof(**output));
-
-		(*output)[num - 1] = cur;
-		cur += strlen(cur) + 1;
-	}
-	(*output)[num] = NULL;
-	return num;
-}
-
-static int parse_exec_params(char ***argv, char ***envp)
-{
-	int ret;
-	char *cmdline = NULL, *env = NULL;
-	size_t cmdline_size, env_size;
-
-	cmdline = file_to_buf("/proc/self/cmdline", &cmdline_size);
-	if (!cmdline)
-		goto on_error;
-
-	env = file_to_buf("/proc/self/environ", &env_size);
-	if (!env)
-		goto on_error;
-
-	ret = push_vargs(cmdline, cmdline_size, argv);
-	if (ret <= 0)
-		goto on_error;
-
-	ret = push_vargs(env, env_size, envp);
-	if (ret <= 0)
-		goto on_error;
-
-	return 0;
-
-on_error:
-	free(env);
-	free(cmdline);
-
-	return -1;
-}
-
 static int is_memfd(void)
 {
 	int fd, saved_errno, seals;
@@ -142,10 +91,9 @@ on_error:
 	errno = saved_errno;
 }
 
-int lxc_rexec(const char *memfd_name)
+int lxc_rexec(char *argv[], const char *memfd_name)
 {
 	int ret;
-	char **argv = NULL, **envp = NULL;
 
 	ret = is_memfd();
 	if (ret < 0 && ret == -ENOTRECOVERABLE) {
@@ -157,15 +105,7 @@ int lxc_rexec(const char *memfd_name)
 		return 0;
 	}
 
-	ret = parse_exec_params(&argv, &envp);
-	if (ret < 0) {
-		fprintf(stderr,
-			"%s - Failed to parse command line parameters\n",
-			strerror(errno));
-		return -1;
-	}
-
-	lxc_rexec_as_memfd(argv, envp, memfd_name);
+	lxc_rexec_as_memfd(argv, environ, memfd_name);
 	fprintf(stderr, "%s - Failed to rexec as memfd\n", strerror(errno));
 	return -1;
 }
@@ -177,9 +117,9 @@ int lxc_rexec(const char *memfd_name)
  * container are in the same user namespace or have set up an identity id
  * mapping: CVE-2019-5736.
  */
-__attribute__((constructor)) static void liblxc_rexec(void)
+__attribute__((constructor)) static void liblxc_rexec(int argc, char *argv[])
 {
-	if (getenv("LXC_MEMFD_REXEC") && lxc_rexec("liblxc")) {
+	if (getenv("LXC_MEMFD_REXEC") && lxc_rexec(argv, "liblxc")) {
 		fprintf(stderr, "Failed to re-execute liblxc via memory file descriptor\n");
 		_exit(EXIT_FAILURE);
 	}

src/lxc/rexec.h

@@ -21,6 +21,6 @@
 #ifndef __LXC_REXEC_H
 #define __LXC_REXEC_H
 
-extern int lxc_rexec(const char *memfd_name);
+extern int lxc_rexec(char *argv[], const char *memfd_name);
 
 #endif /* __LXC_REXEC_H */

src/lxc/tools/lxc_attach.c

@@ -57,9 +57,9 @@ lxc_log_define(lxc_attach, lxc);
  * mapping: CVE-2019-5736.
  */
 #ifdef ENFORCE_MEMFD_REXEC
-__attribute__((constructor)) static void lxc_attach_rexec(void)
+__attribute__((constructor)) static void lxc_attach_rexec(int argc, char *argv[])
 {
-	if (!getenv("LXC_MEMFD_REXEC") && lxc_rexec("lxc-attach")) {
+	if (!getenv("LXC_MEMFD_REXEC") && lxc_rexec(argv, "lxc-attach")) {
 		fprintf(stderr, "Failed to re-execute lxc-attach via memory file descriptor\n");
 		_exit(EXIT_FAILURE);
 	}