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