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 14ca1f1c3fb0dc7ed78a8029dab489e99298d2f8..e42a905180f00f93d3113fbdb2922bf5b1bb2217 100644 (file)
--- a/net/ipv4/esp4.c
+++ b/net/ipv4/esp4.c
@@ -23,6 +23,8 @@ struct esp_skb_cb {
 
 #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 @@ static int esp_output(struct xfrm_state *x, struct sk_buff *skb)
        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 @@ static int esp_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));