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xfrm: Traffic Flow Confidentiality for IPv6 ESP

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Add TFC padding to all packets smaller than the boundary configured
on the xfrm state. If the boundary is larger than the PMTU, limit
padding to the PMTU.

Signed-off-by: Martin Willi <martin@strongswan.org>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Martin Willi 2010-12-08 04:37:51 +00:00 committed by David S. Miller
parent d979e20f2b
commit 040253c931
1 changed files with 24 additions and 8 deletions
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32
net/ipv6/esp6.c
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@ -49,6 +49,8 @@ struct esp_skb_cb {
#define ESP_SKB_CB(__skb) ((struct esp_skb_cb *)&((__skb)->cb[0]))
static u32 esp6_get_mtu(struct xfrm_state *x, int mtu);
/*
* Allocate an AEAD request structure with extra space for SG and IV.
*
@ -140,6 +142,8 @@ static int esp6_output(struct xfrm_state *x, struct sk_buff *skb)
int blksize;
int clen;
int alen;
int plen;
int tfclen;
int nfrags;
u8 *iv;
u8 *tail;
@ -148,18 +152,26 @@ static int esp6_output(struct xfrm_state *x, struct sk_buff *skb)
/* skb is pure payload to encrypt */
err = -ENOMEM;
/* Round to block size */
clen = skb->len;
aead = esp->aead;
alen = crypto_aead_authsize(aead);
tfclen = 0;
if (x->tfcpad) {
struct xfrm_dst *dst = (struct xfrm_dst *)skb_dst(skb);
u32 padto;
padto = min(x->tfcpad, esp6_get_mtu(x, dst->child_mtu_cached));
if (skb->len < padto)
tfclen = padto - skb->len;
}
blksize = ALIGN(crypto_aead_blocksize(aead), 4);
clen = ALIGN(clen + 2, blksize);
clen = ALIGN(skb->len + 2 + tfclen, blksize);
if (esp->padlen)
clen = ALIGN(clen, esp->padlen);
plen = clen - skb->len - tfclen;
if ((err = skb_cow_data(skb, clen - skb->len + alen, &trailer)) < 0)
err = skb_cow_data(skb, tfclen + plen + alen, &trailer);
if (err < 0)
goto error;
nfrags = err;
@ -174,13 +186,17 @@ static int esp6_output(struct xfrm_state *x, struct sk_buff *skb)
/* Fill padding... */
tail = skb_tail_pointer(trailer);
if (tfclen) {
memset(tail, 0, tfclen);
tail += tfclen;
}
do {
int i;
for (i=0; i<clen-skb->len - 2; i++)
for (i = 0; i < plen - 2; i++)
tail[i] = i + 1;
} while (0);
tail[clen-skb->len - 2] = (clen - skb->len) - 2;
tail[clen - skb->len - 1] = *skb_mac_header(skb);
tail[plen - 2] = plen - 2;
tail[plen - 1] = *skb_mac_header(skb);
pskb_put(skb, trailer, clen - skb->len + alen);
skb_push(skb, -skb_network_offset(skb));