Re: /lib/ld-2.2.4.so

[Michal Podsedník <podsednik () gecom cz>]

Sabau Daniel wrote:
> lrwxrwxrwx    1 root     root           11 Apr 15 12:01 /lib/ld-linux.so.2
> -> ld-2.2.4.so
>
>       This file gives users the ability of running binaries on witch the
> user doesn't have the permission to execute, it is enough to have read
> ability on the file in order to execute it:
>
> -rwxr-xr--    1 root     root        45948 Aug  9  2001 /bin/ls
>
> but using the /lib/ld-2.2.4.so file i can execute the ls command:

Remember, when the binary is +r, you can always copy it anywhere else and 
chmod it +x.

> [08:51:36][draven@Zero:~]:$/lib/ld-2.2.4.so /bin/ls /
> bin   bzImage   bzImage3  bzImage5  dev  home    lib   mnt  proc  sbin
> usr
> boot  bzImage2  bzImage4  bzImage6  etc  initrd  misc  opt  root  tmp
...
> The most interesting part is running binaries on partitions mounted with
> noexec, lets take this partition:
>
> /dev/sda9 on /home/friends type ext2
> (rw,noexec,nosuid,nodev,usrquota,grpquota)

Same case as above.

> the important thing is to include a full path in the binary name to be
> able to execute it.
> in the same way i've managed to run the ptrace exploit on a nosuid
> partition
> i'm running a 2.4.18 kernel with grsecurity-1.9.4 patch on a Red Hat
> Linux 7.2 box, but i've succeded running this file on different linux
> boxes and i've been succesfull, please if anyone know how to eliminate
> this hole in my security give me a replay. If i try to change the mode on
> /lib/ls-2.2.4.so to 700, the users will not be able to login on my linux
> box, so this is not a solution:)

This is not a bug at all. /lib/ld.so is a helper program to load, prepare and 
run ELF binaries. All it actually needs is the permission to read the binary 
into memory. If you don't want your users to run certain binaries, make these 
-r also. Making binaries -x while keeping them +r is pointless.

Bye,
-- 
Michal Podsedník
podsednik () gecom cz
(+420) 0603 105 261