Bug 1109263 (CVE-2014-4043)

posix_spawn_file_actions_addopen in glibc fails to copy the path argument.
Per the specification (http://pubs.opengroup.org/onlinepubs/000095399/functions/posix_spawn_file_actions_addclose.html) it is supposed to.
The result of not copying is that programs can easily trigger use-after-free bugs,
or other situations where the path is mutated. The following program demonstrates this issue:

#include <string.h>
#include <assert.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <stdlib.h>
#include <spawn.h>
#include <stdio.h>


extern char *const *environ;

int main() {
    int res;
    posix_spawn_file_actions_t fa;
    posix_spawn_file_actions_init(&fa);

    char *orig_path = "/tmp/afddsa";
    char *path = malloc(strlen(orig_path) + 1);
    strcpy(path, orig_path);
    path[strlen(orig_path)] = '\0';

    res = posix_spawn_file_actions_addopen(
        &fa, 1, path, O_WRONLY | O_CREAT, S_IRUSR | S_IWUSR);
    assert(res == 0);

    memset(path, 0, strlen(orig_path));
    free(path);

    char *argv[] = {"/bin/echo", NULL};
    pid_t pid;
    res = posix_spawn(
        &pid,
        "/bin/echo",
        &fa,
        NULL,
        argv,
        environ
    );
    assert(res == 0);
    int status;
    wait4(pid, &status, 0, NULL);
    printf("%d\n", WEXITSTATUS(status));
}

This bug was jointly discovered by David Reid, Alex Gaynor, and Glyph Lefkowitz.

Issue is fixed in glibc 2.20:
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=89e435f3559c53084498e9baad22172b64429362
Recommended additional commit for backporting: 
https://sourceware.org/git/?p=glibc.git;a=commit;h=35a5e3e338ae17f3d42c6

External references:

https://sourceware.org/bugzilla/show_bug.cgi?id=17048