From: Christian Brauner <christian.brauner@ubuntu.com>
Date: Thu, 14 Feb 2019 13:48:41 +0000 (+0100)
Subject: rexec: remove envp parsing in favour of environ
X-Git-Tag: lxc-3.2.0~148^2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=cee55b59cd0f7446bae25d02bcd23805ce43aaa4;p=thirdparty%2Flxc.git

rexec: remove envp parsing in favour of environ

My first attempt to simplify this and make it less costly focussed on
the way constructors are called. I was under the impression that the ELF
specification mandated that arg, argv, and actually even envp need to be
passed to functions located in the .init_array section (aka
"constructors"). Actually, the specifications is (cf. [2]):

SHT_INIT_ARRAY
This section contains an array of pointers to initialization functions,
as described in ``Initialization and Termination Functions'' in Chapter
5. Each pointer in the array is taken as a parameterless procedure with
a void return.

which means that this becomes a libc specific decision. Glibc passes
down those args, musl doesn't. So this approach can't work. However, we
can at least remove the environment parsing part based on POSIX since
[1] mandates that there should be an environ variable defined in
unistd.h which provides access to the environment. See also the relevant
Open Group specification [1].

[1]: http://pubs.opengroup.org/onlinepubs/9699919799/
[2]: http://www.sco.com/developers/gabi/latest/ch4.sheader.html#init_array

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---

diff --git a/src/lxc/rexec.c b/src/lxc/rexec.c
index 024728d85..fe362f284 100644
--- a/src/lxc/rexec.c
+++ b/src/lxc/rexec.c
@@ -25,9 +25,12 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
 
 #include "config.h"
 #include "file_utils.h"
+#include "macro.h"
+#include "memory_utils.h"
 #include "raw_syscalls.h"
 #include "string_utils.h"
 #include "syscall_wrappers.h"
@@ -60,35 +63,22 @@ static int push_vargs(char *data, int data_length, char ***output)
 	return num;
 }
 
-static int parse_exec_params(char ***argv, char ***envp)
+static int parse_argv(char ***argv)
 {
+	__do_free char *cmdline = NULL;
 	int ret;
-	char *cmdline = NULL, *env = NULL;
-	size_t cmdline_size, env_size;
+	size_t cmdline_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;
+		return -1;
 
 	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 -1;
 
+	steal_ptr(cmdline);
 	return 0;
-
-on_error:
-	free(env);
-	free(cmdline);
-
-	return -1;
 }
 
 static int is_memfd(void)
@@ -142,10 +132,16 @@ on_error:
 	errno = saved_errno;
 }
 
+/*
+ * Get cheap access to the environment. This must be declared by the user as
+ * mandated by POSIX. The definition is located in unistd.h.
+ */
+extern char **environ;
+
 int lxc_rexec(const char *memfd_name)
 {
 	int ret;
-	char **argv = NULL, **envp = NULL;
+	char **argv = NULL;
 
 	ret = is_memfd();
 	if (ret < 0 && ret == -ENOTRECOVERABLE) {
@@ -157,7 +153,7 @@ int lxc_rexec(const char *memfd_name)
 		return 0;
 	}
 
-	ret = parse_exec_params(&argv, &envp);
+	ret = parse_argv(&argv);
 	if (ret < 0) {
 		fprintf(stderr,
 			"%s - Failed to parse command line parameters\n",
@@ -165,7 +161,7 @@ int lxc_rexec(const char *memfd_name)
 		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;
 }