Błędy, błędy …

Kolejny raz za sprawą panów z iSEC Security Research zmuszeni jesteśmy rekompilować nasze kernele. Tym razem błąd wykryty został w funkcji mremap. Na atak podatne są kernele z serii 2.4 i 2.6. Pełne advisory poniżej.
Update: Jak wyjaśnił Paul Starzetz w swoim poście kernele z serii 2.2 nie są podatne na wyżej wymieniony błąd. Pełną wiadomość można przeczytać tutaj.

  Synopsis:  Linux kernel do_mremap local privilege escalation vulnerability  Product:   Linux kernel  Version:   2.2, 2.4 and 2.6 series    Vendor:    http://www.kernel.org/  URL:       http://isec.pl/vulnerabilities/isec-0013-mremap.txt  CVE:       http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2003-0985  Author:    Paul Starzetz ,             Wojciech Purczynski   Date:      January 5, 2004      Issue:  ======    A critical security vulnerability has been found  in  the  Linux  kernel  memory  management  code in mremap(2) system call due to incorrect bound  checks.      Details:  ========    The mremap system call provides functionality of resizing (shrinking  or  growing)  as well as moving across process's addressable space of existing  virtual memory areas (VMAs) or any of its parts.    A typical VMA covers at least one memory page (which is exactly  4kB  on  the i386  architecture). An incorrect bound check discovered inside the  do_mremap() kernel code performing remapping of a virtual memory  area  may lead to creation of a virtual memory area of 0 bytes length.    The problem bases on the general mremap flaw that remapping of 2 pages  from inside a VMA creates a memory hole of only one page in length but  an additional  VMA  of two pages. In the case of a zero sized remapping  request no VMA hole is created but an additional VMA descriptor of 0  bytes in length is created.    Such a malicious virtual memory area may disrupt the operation of other  parts of the kernel memory management subroutines finally leading to   unexpected behavior.    A typical process's memory layout showing invalid VMA created with  mremap system call:        08048000-0804c000 r-xp 00000000 03:05 959142     /tmp/test      0804c000-0804d000 rw-p 00003000 03:05 959142     /tmp/test      0804d000-0804e000 rwxp 00000000 00:00 0      40000000-40014000 r-xp 00000000 03:05 1544523    /lib/ld-2.3.2.so      40014000-40015000 rw-p 00013000 03:05 1544523    /lib/ld-2.3.2.so      40015000-40016000 rw-p 00000000 00:00 0      4002c000-40158000 r-xp 00000000 03:05 1544529    /lib/libc.so.6      40158000-4015d000 rw-p 0012b000 03:05 1544529    /lib/libc.so.6      4015d000-4015f000 rw-p 00000000 00:00 0  [*] 60000000-60000000 rwxp 00000000 00:00 0      bfffe000-c0000000 rwxp fffff000 00:00 0    The broken VMA in the above example has been marked with a [*].      Impact:  =======    Since no special privileges are required to use the mremap(2) system  call any process may misuse its unexpected behavior to disrupt the kernel  memory management subsystem. Proper exploitation of this vulnerability may  lead to local privilege escalation including execution of  arbitrary  code  with kernel level access. Proof-of-concept exploit code has been created   and successfully tested giving UID 0 shell on vulnerable systems.    The exploitability of the discovered vulnerability is possible, although  not a trivial one. We have identified at least two different attack   vectors for the  2.4 kernel series. All users are encouraged to patch all  vulnerable systems as soon as appropriate vendor patches are released.      Credits:  ========    Paul Starzetz  has identified the vulnerability and  performed further research.       Disclaimer:  ===========    This  document and all the information it contains are provided "as is",  for educational purposes only, without warranty of any kind, whether   express or implied.    The  authors reserve the right not to be responsible for the topicality,  correctness, completeness or quality of the information provided in  this document. Liability claims regarding damage caused by the use of  any information provided, including any kind of information which is  incomplete or incorrect, will therefore be rejected.  

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