CVE-2013-1792 Linux kernel: KEYS: race with concurrent install_user_keyrings()

[P J P <ppandit () redhat com>]

   Hello,

Mateusz Guzik of Red Hat discovered a race condition in 
install_user_keyrings() routine, leading to a NULL pointer dereference. It 
occurs during parallel invocation of the install_user_keyrings & 
lookup_user_key routines, for the same user, if `uid' and `uid-session' 
keyrings are not yet created.

An unprivileged user could use this flaw to crash the system, resulting in 
DoS.

Upstream fix:
-------------
 -> https://lkml.org/lkml/2013/3/6/535

Reference:
----------
 -> https://bugzilla.redhat.com/show_bug.cgi?id=916646

Thank you.
--
Prasad J Pandit / Red Hat Security Response Team
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