If configured on xfrm state, increase the length of all packets to
a given boundary using TFC padding as specified in RFC4303. For
transport mode, or if the XFRM_TFC_ESPV3 is not set, grow the ESP
padding field instead.
Signed-off-by: Martin Willi <mar...@strongswan.org>
---
net/ipv4/esp4.c | 42 +++++++++++++++++++++++++++++++++---------
1 files changed, 33 insertions(+), 9 deletions(-)
diff --git a/net/ipv4/esp4.c b/net/ipv4/esp4.c
index 67e4c12..a6adfbc 100644
--- a/net/ipv4/esp4.c
+++ b/net/ipv4/esp4.c
@@ -117,23 +117,43 @@ static int esp_output(struct xfrm_state *x, struct
sk_buff *skb)
int blksize;
int clen;
int alen;
+ int plen;
+ int tfclen;
+ int tfcpadto;
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);
blksize = ALIGN(crypto_aead_blocksize(aead), 4);
- clen = ALIGN(clen + 2, blksize);
-
- if ((err = skb_cow_data(skb, clen - skb->len + alen, &trailer)) < 0)
+ tfclen = 0;
+ tfcpadto = x->tfc.pad;
+
+ if (skb->len >= tfcpadto) {
+ clen = ALIGN(skb->len + 2, blksize);
+ } else if (x->tfc.flags & XFRM_TFC_ESPV3 &&
+ x->props.mode == XFRM_MODE_TUNNEL) {
+ /* ESPv3 TFC padding, append bytes to payload */
+ tfclen = tfcpadto - skb->len;
+ clen = ALIGN(skb->len + 2 + tfclen, blksize);
+ } else {
+ /* ESPv2 TFC padding. If we exceed the 255 byte maximum, use
+ * random padding to hide payload length as good as possible. */
+ clen = ALIGN(skb->len + 2 + tfcpadto - skb->len, blksize);
+ if (clen - skb->len - 2 > 255) {
+ clen = ALIGN(skb->len + (u8)random32() + 2, blksize);
+ if (clen - skb->len - 2 > 255)
+ clen -= blksize;
+ }
+ }
+ plen = clen - skb->len - tfclen;
+ err = skb_cow_data(skb, tfclen + plen + alen, &trailer);
+ if (err < 0)
goto error;
nfrags = err;
@@ -148,13 +168,17 @@ 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));
--
1.7.1
--
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