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 024728d855d484dacfdd9608d80bd9fe31da6429..fe362f284db0dd329acd735050e9e3bccafe862b 100644 (file)
--- 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;
 }