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[PATCH 4.9 14/32] tun: read vnet_hdr_sz once

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4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Willem de Bruijn <willemb@google.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@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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/net/tun.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1187,9 +1187,11 @@ 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))
@@ -1201,7 +1203,7 @@ 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) {
@@ -1348,7 +1350,7 @@ 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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[PATCH 4.9 00/32] 4.9.11-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:00 +0100
  [PATCH 4.9 08/32] net: use a work queue to defer net_disable_timestamp() work Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:00 +0100
  [PATCH 4.9 27/32] net: dsa: Do not destroy invalid network devices Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:00 +0100
  [PATCH 4.9 24/32] net: introduce device min_header_len Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:00 +0100
  [PATCH 4.9 17/32] rtl8150: Use heap buffers for all register access Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:00 +0100
  [PATCH 4.9 21/32] sctp: avoid BUG_ON on sctp_wait_for_sndbuf Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:00 +0100
  [PATCH 4.9 04/32] ipv6: fix ip6_tnl_parse_tlv_enc_lim() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:00 +0100
  [PATCH 4.9 07/32] stmmac: Discard masked flags in interrupt status register Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:00 +0100
  [PATCH 4.9 05/32] ipv6: pointer math error in ip6_tnl_parse_tlv_enc_lim() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:00 +0100
  [PATCH 4.9 32/32] net/mlx5: Dont unlock fte while still using it Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:00 +0100
  [PATCH 4.9 09/32] ipv4: keep skb->dst around in presence of IP options Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:00 +0100
  [PATCH 4.9 29/32] mld: do not remove mld souce list info when set link down Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:00 +0100
  [PATCH 4.9 06/32] tcp: fix 0 divide in __tcp_select_window() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:00 +0100
  [PATCH 4.9 23/32] sit: fix a double free on error path Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:10 +0100
  [PATCH 4.9 03/32] net/sched: matchall: Fix configuration race Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:10 +0100
  [PATCH 4.9 19/32] catc: Use heap buffer for memory size test Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:10 +0100
  [PATCH 4.9 22/32] lwtunnel: valid encap attr check should return 0 when lwtunnel is disabled Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:10 +0100
  [PATCH 4.9 11/32] ip6_gre: fix ip6gre_err() invalid reads Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:10 +0100
  [PATCH 4.9 15/32] macvtap: read vnet_hdr_size once Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:10 +0100
  [PATCH 4.9 20/32] mlx4: Invoke softirqs after napi_reschedule Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:10 +0100
  [PATCH 4.9 14/32] tun: read vnet_hdr_sz once Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:10 +0100
  [PATCH 4.9 13/32] tcp: avoid infinite loop in tcp_splice_read() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:10 +0100
  [PATCH 4.9 18/32] catc: Combine failure cleanup code in catc_probe() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:10 +0100
  [PATCH 4.9 02/32] net/mlx5e: Fix update of hash function/key via ethtool Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:10 +0100
  [PATCH 4.9 12/32] ipv6: tcp: add a missing tcp_v6_restore_cb() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:10 +0100
  [PATCH 4.9 28/32] l2tp: do not use udp_ioctl() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:10 +0100
  [PATCH 4.9 25/32] packet: round up linear to header len Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:10 +0100
  [PATCH 4.9 10/32] netlabel: out of bound access in cipso_v4_validate() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:10 +0100
  [PATCH 4.9 01/32] can: Fix kernel panic at security_sock_rcv_skb Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-16 19:10 +0100
  Re: [PATCH 4.9 00/32] 4.9.11-stable review Guenter Roeck <linux@roeck-us.net> - 2017-02-17 11:40 +0100
    Re: [PATCH 4.9 00/32] 4.9.11-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-17 19:20 +0100
  Re: [PATCH 4.9 00/32] 4.9.11-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-02-18 00:50 +0100
    Re: [PATCH 4.9 00/32] 4.9.11-stable review Kevin Hilman <khilman@baylibre.com> - 2017-02-20 23:40 +0100

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