xfrm: Traffic Flow Confidentiality for IPv4 ESP
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>
diff --git a/net/ipv4/esp4.c b/net/ipv4/esp4.c
index 14ca1f1..e42a905 100644
--- a/net/ipv4/esp4.c
+++ b/net/ipv4/esp4.c
@@ -23,6 +23,8 @@
#define ESP_SKB_CB(__skb) ((struct esp_skb_cb *)&((__skb)->cb[0]))
+static u32 esp4_get_mtu(struct xfrm_state *x, int mtu);
+
/*
* Allocate an AEAD request structure with extra space for SG and IV.
*
@@ -117,25 +119,35 @@
int blksize;
int clen;
int alen;
+ int plen;
+ int tfclen;
int nfrags;
/* skb is pure payload to encrypt */
err = -ENOMEM;
- /* Round to block size */
- clen = skb->len;
-
esp = x->data;
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, esp4_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;
@@ -150,13 +162,17 @@
/* 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));