[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>

include/net/esp.h

@@ -15,13 +15,14 @@ struct esp_data
 	struct {
 		u8			*key;		/* Key */
 		int			key_len;	/* Key length */
-		u8			*ivec;		/* ivec buffer */
+		int			padlen;		/* 0..255 */
 		/* ivlen is offset from enc_data, where encrypted data start.
 		 * It is logically different of crypto_tfm_alg_ivsize(tfm).
 		 * We assume that it is either zero (no ivec), or
 		 * >= crypto_tfm_alg_ivsize(tfm). */
 		int			ivlen;
-		int			padlen;		/* 0..255 */
+		int			ivinitted;
+		u8			*ivec;		/* ivec buffer */
 		struct crypto_blkcipher	*tfm;		/* crypto handle */
 	} conf;
 

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;

net/ipv6/esp6.c

@@ -99,8 +99,13 @@ static int esp6_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];
@@ -353,7 +358,7 @@ static int esp6_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;