[IPSEC] esp: Defer output IV initialization to first use.

First of all, if the xfrm_state only gets used for input
packets this entropy is a complete waste.

Secondly, it is often the case that a configuration loads
many rules (perhaps even dynamically) and they don't all
necessarily ever get used.

This get_random_bytes() call was showing up in the profiles
for xfrm_state inserts which is how I noticed this.

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 2 deletions

diff --git a/net/ipv4/esp4.c b/net/ipv4/esp4.c
index e87377e1d6b..13b29360d10 100644
--- a/net/ipv4/esp4.c
+++ b/net/ipv4/esp4.c
@@ -95,8 +95,13 @@ static int esp_output(struct xfrm_state *x, struct sk_buff *skb)
 	esph->seq_no = htonl(++x->replay.oseq);
 	xfrm_aevent_doreplay(x);
 
-	if (esp->conf.ivlen)
+	if (esp->conf.ivlen) {
+		if (unlikely(!esp->conf.ivinitted)) {
+			get_random_bytes(esp->conf.ivec, esp->conf.ivlen);
+			esp->conf.ivinitted = 1;
+		}
 		crypto_blkcipher_set_iv(tfm, esp->conf.ivec, esp->conf.ivlen);
+	}
 
 	do {
 		struct scatterlist *sg = &esp->sgbuf[0];
@@ -378,7 +383,7 @@ static int esp_init_state(struct xfrm_state *x)
 		esp->conf.ivec = kmalloc(esp->conf.ivlen, GFP_KERNEL);
 		if (unlikely(esp->conf.ivec == NULL))
 			goto error;
-		get_random_bytes(esp->conf.ivec, esp->conf.ivlen);
+		esp->conf.ivinitted = 0;
 	}
 	if (crypto_blkcipher_setkey(tfm, esp->conf.key, esp->conf.key_len))
 		goto error;