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tun: read vnet_hdr_sz once

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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>
This commit is contained in:
Willem de Bruijn 2017-02-03 18:20:48 -05:00 committed by David S. Miller
parent ccf7abb93a
commit e1edab87fa
1 changed files with 6 additions and 4 deletions
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10
drivers/net/tun.c
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@ -1170,9 +1170,11 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
}
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;
if (!copy_from_iter_full(&gso, sizeof(gso), from))
return -EFAULT;
@ -1183,7 +1185,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
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) {
@ -1335,7 +1337,7 @@ static ssize_t tun_put_user(struct tun_struct *tun,
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;