Linux Kernel 2.6.38 Remote NULL Pointer Dereference
====================================================

[Advisory Information]
Title:    Linux kernel 2.6.38: Remote NULL pointer dereference
Release date:   11/05/2011
Last update:   11/05/2011

Credits:   
   Aristide Fattori, Università degli Studi di Milano (joystick@security.dico.unimi.it)
  Roberto Paleari,  Emaze Networks S.p.A (roberto.paleari@emaze.net)

[Vulnerability Information]
Class:          Remote NULL pointer dereference
CVE:          

[Affected Software]

We confirm the presence of this vulnerability in the following kernel versions:

- Linux kernel 2.6.38.6 (vanilla)
- Linux kernel 2.6.38.4 (vanilla)
- Linux kernel 2.6.38.3 (vanilla)
- Debian kernel image 2.6.38-2-686

Other Linux kernel versions could be also affected by this issue.

[Vulnerability Details] 

In function icmp_send() (net/ipv4/icmp.c), the parameter passed to dev_net()
function is not properly validated. This can lead to a NULL pointer dereference
that crashes the kernel.

An attacker can exploit this bug and cause a DoS, both on a specific target or
on any 2.6.38.x machine connected to the local network. To cause the crash, the
attacker must flood the target with fragmented IPv4 packets. Important fields
in the IP packet are:

 * Flags: the MF flag must be set.

 * Fragment ID: using pseudo-random values for this field quickly fills
   fragmented queues in the victim's kernel, as it is unable to easily
   reassemble received packets.

 * TOS: using pseudo-random values for this field trigger the creation of more
   than one route cache entry for the same destination address, increasing the
   chances of incurring in the error condition described before.

Other fields of the packet do not really matter, and they can be set to
arbitrary values.

[Report Timeline]
    * 10/05/2011 - Vendor informed
    * 10/05/2011 - Vendor asked to publicly disclose the details of this issue

[Disclaimer] 
The authors, Emaze Networks S.p.A and Università degli Studi di Milano are not
responsible for the misuse of the information provided in their security
advisories. These advisories are a service to the professional security
community. There are NO WARRANTIES with regard to this information. Any
application or distribution of this information constitutes acceptance AS IS,
at the user's own risk. This information is subject to change without notice.