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Date: Thu, 16 Feb 2017 09:53:41 -0800 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-kernel@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, stable@...r.kernel.org, Willem de Bruijn <willemb@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>, Eric Dumazet <edumazet@...gle.com>, "David S. Miller" <davem@...emloft.net> Subject: [PATCH 4.4 11/20] tun: read vnet_hdr_sz once 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Willem de Bruijn <willemb@...gle.com> [ 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@...gle.com> Reported-by: Dmitry Vyukov <dvyukov@...gle.com> CC: Eric Dumazet <edumazet@...gle.com> Acked-by: Eric Dumazet <edumazet@...gle.com> Signed-off-by: David S. Miller <davem@...emloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> --- drivers/net/tun.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -1108,9 +1108,11 @@ static ssize_t tun_get_user(struct tun_s } if (tun->flags & IFF_VNET_HDR) { - if (len < tun->vnet_hdr_sz) + int vnet_hdr_sz = READ_ONCE(tun->vnet_hdr_sz); + + if (len < vnet_hdr_sz) return -EINVAL; - len -= tun->vnet_hdr_sz; + len -= vnet_hdr_sz; n = copy_from_iter(&gso, sizeof(gso), from); if (n != sizeof(gso)) @@ -1122,7 +1124,7 @@ static ssize_t tun_get_user(struct tun_s if (tun16_to_cpu(tun, gso.hdr_len) > len) return -EINVAL; - iov_iter_advance(from, tun->vnet_hdr_sz - sizeof(gso)); + iov_iter_advance(from, vnet_hdr_sz - sizeof(gso)); } if ((tun->flags & TUN_TYPE_MASK) == IFF_TAP) { @@ -1301,7 +1303,7 @@ static ssize_t tun_put_user(struct tun_s vlan_hlen = VLAN_HLEN; if (tun->flags & IFF_VNET_HDR) - vnet_hdr_sz = tun->vnet_hdr_sz; + vnet_hdr_sz = READ_ONCE(tun->vnet_hdr_sz); total = skb->len + vlan_hlen + vnet_hdr_sz;
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