This is a note to let you know that I've just added the patch titled tun: read vnet_hdr_sz once to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: tun-read-vnet_hdr_sz-once.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From foo@baz Tue Feb 14 16:29:59 PST 2017 From: Willem de Bruijn <willemb@xxxxxxxxxx> Date: Fri, 3 Feb 2017 18:20:48 -0500 Subject: tun: read vnet_hdr_sz once From: Willem de Bruijn <willemb@xxxxxxxxxx> [ 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@xxxxxxxxxx> Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx> CC: Eric Dumazet <edumazet@xxxxxxxxxx> Acked-by: Eric Dumazet <edumazet@xxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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; Patches currently in stable-queue which might be from willemb@xxxxxxxxxx are queue-4.4/packet-round-up-linear-to-header-len.patch queue-4.4/tun-read-vnet_hdr_sz-once.patch queue-4.4/ipv6-fix-ip6_tnl_parse_tlv_enc_lim.patch queue-4.4/net-introduce-device-min_header_len.patch queue-4.4/macvtap-read-vnet_hdr_size-once.patch