Revert "rexec: remove needless /proc/cmdline parsing"

src/lxc/rexec.c

@@ -25,7 +25,6 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <unistd.h>
 
 #include "config.h"
 #include "file_utils.h"
@@ -40,6 +39,58 @@
 #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;
@@ -91,9 +142,10 @@ on_error:
 	errno = saved_errno;
 }
 
-int lxc_rexec(char *argv[], const char *memfd_name)
+int lxc_rexec(const char *memfd_name)
 {
 	int ret;
+	char **argv = NULL, **envp = NULL;
 
 	ret = is_memfd();
 	if (ret < 0 && ret == -ENOTRECOVERABLE) {
@@ -105,7 +157,15 @@ int lxc_rexec(char *argv[], const char *memfd_name)
 		return 0;
 	}
 
-	lxc_rexec_as_memfd(argv, environ, memfd_name);
+	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);
 	fprintf(stderr, "%s - Failed to rexec as memfd\n", strerror(errno));
 	return -1;
 }
@@ -117,9 +177,9 @@ int lxc_rexec(char *argv[], 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(int argc, char *argv[])
+__attribute__((constructor)) static void liblxc_rexec(void)
 {
-	if (getenv("LXC_MEMFD_REXEC") && lxc_rexec(argv, "liblxc")) {
+	if (getenv("LXC_MEMFD_REXEC") && lxc_rexec("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(char *argv[], const char *memfd_name);
+extern int lxc_rexec(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(int argc, char *argv[])
+__attribute__((constructor)) static void lxc_attach_rexec(void)
 {
-	if (!getenv("LXC_MEMFD_REXEC") && lxc_rexec(argv, "lxc-attach")) {
+	if (!getenv("LXC_MEMFD_REXEC") && lxc_rexec("lxc-attach")) {
 		fprintf(stderr, "Failed to re-execute lxc-attach via memory file descriptor\n");
 		_exit(EXIT_FAILURE);
 	}