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Hi,

while looking at the changelog for 2.4.28, I've found, that a bug I 
independently came over some days ago has been fixed in that release:

David S. Miller:
  o [AF_UNIX]: Serialize dgram read using semaphore just like stream

That fixes missing serialization in unix_dgram_recvmsg().

I was slightly suprised reading the 2.4.27 code and I strongly believe 
that the flaw is fully exploitable to gain elevated privileges. 

There is a subtle race condition finally permitting a non-root user to 
increment (up to 256 times) any arbitrary location(s) in kernel space.

The condition is not easy to exploit since an attacker must trick 
kmalloc() to sleep on allocation of a special chunk of memory and then 
convince the scheduler to execute another thread. But it is feasible.

Conclusion: update as quick as possible to 2.4.28.

- -- 
Paul Starzetz
iSEC Security Research
http://isec.pl/

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