Bluetooth: Prevent buffer overflow in l2cap config request, CVE-2011-2497

Bluetooth: Prevent buffer overflow in l2cap config request, CVE-2011-2497

A remote user can provide a small value for the command size field in
the command header of an l2cap configuration request, resulting in an
integer underflow when subtracting the size of the configuration request
header.  This results in copying a very large amount of data via
memcpy() and destroying the kernel heap.  Check for underflow.

Signed-off-by: Dan Rosenberg <drosenberg@vsecurity.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>

(backported from commit 7ac28817536797fd40e9646452183606f9e17f71)
CVE-2011-2497
BugLink: http://bugs.launchpad.net/bugs/838423
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>