From: Willem de Bruijn <willemb@google.com>
Date: Fri, 3 Feb 2017 23:20:48 +0000 (-0500)
Subject: tun: read vnet_hdr_sz once
X-Git-Tag: v3.2.87~12
X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?p=pandora-kernel.git;a=commitdiff_plain;h=6451245e668c7c1d28f988e733c5c332708a1b52;hp=6451245e668c7c1d28f988e733c5c332708a1b52;ds=inline

tun: read vnet_hdr_sz once

[ Upstream commit e1edab87faf6ca30cd137e0795bc73aa9a9a22ec ]

When IFF_VNET_HDR is enabled, a virtio_net header must precede data.
Data length is verified to be greater than or equal to expected header
length tun->vnet_hdr_sz before copying.

Read this value once and cache locally, as it can be updated between
the test and use (TOCTOU).

Signed-off-by: Willem de Bruijn <willemb@google.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
CC: Eric Dumazet <edumazet@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2:
 - Use ACCESS_ONCE() instead of READ_ONCE()
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---