net: avoid infinite loop when receiving packets(CVE-2015-5278)

net: avoid infinite loop when receiving packets(CVE-2015-5278)

Ne2000 NIC uses ring buffer of NE2000_MEM_SIZE(49152)
bytes to process network packets. While receiving packets
via ne2000_receive() routine, a local 'index' variable
could exceed the ring buffer size, leading to an infinite
loop situation.

Reported-by: Qinghao Tang <luodalongde@gmail.com>
Signed-off-by: P J P <pjp@fedoraproject.org>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
(cherry picked from commit 737d2b3c41d59eb8f94ab7eb419b957938f24943)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>