Bug#692783: libc6: fcloseall() doesn't close any streams

[Piotr Engelking <inkerman42@gmail.com>]

Package: libc6
Version: 2.13-36
Severity: normal
Tags: security

The fcloseall() function is supposed to close all open streams,
including std{in,out,err}. It doesn't close any:

$ cat fcloseall.c
#define _GNU_SOURCE

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void
syserr(char *msg)
{
    fflush(NULL);
    fprintf(stderr, "%s: %s\n", msg, strerror(errno));

    exit(EXIT_FAILURE);
}

int
main(void)
{
    FILE *nulldev = fopen("/dev/null", "r");
    char data[1];

    if (!nulldev)
        syserr("fopen");

    if (fcloseall())
        syserr("fcloseall");

    fread(data, sizeof(data), 1, nulldev);

    if (ferror(nulldev))
        syserr("fread");

    return 0;
}
$ gcc -Wall -Wextra -fno-builtin fcloseall.c
$ ./a.out; echo $?
0
$

The bug may also result in a security problem if a program like
'start-stop-daemon -c' uses fcloseall() to close its file descriptors.


-- System Information:
Debian Release: wheezy/sid
  APT prefers testing
  APT policy: (500, 'testing'), (400, 'unstable'), (300, 'experimental')
Architecture: i386 (x86_64)

Kernel: Linux 3.6.5 (SMP w/2 CPU cores)
Locale: LANG=C.UTF-8, LC_CTYPE=C.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages libc6 depends on:
ii  libc-bin  2.13-36
ii  libgcc1   1:4.7.1-7

Versions of packages libc6 recommends:
ii  libc6-i686  2.13-36

Versions of packages libc6 suggests:
ii  debconf [debconf-2.0]  1.5.46
ii  glibc-doc              2.13-36
ii  locales                2.13-36

-- debconf information excluded