tls: reduce size of tls_cipher_size_desc

tls_cipher_size_desc indexes ciphers by their type, but we're not
using indices 0..50 of the array. Each struct tls_cipher_size_desc is
20B, so that's a lot of unused memory. We can reindex the array
starting at the lowest used cipher_type.

Introduce the get_cipher_size_desc helper to find the right item and
avoid out-of-bounds accesses, and make tls_cipher_size_desc's size
explicit so that gcc reminds us to update TLS_CIPHER_MIN/MAX when we
add a new cipher.
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Link: https://lore.kernel.org/r/5e054e370e240247a5d37881a1cd93a67c15f4ca.1692977948.git.sd@queasysnail.netSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/tls/tls.h

@@ -59,7 +59,18 @@ struct tls_cipher_size_desc {
 	unsigned int rec_seq;
 };
 
-extern const struct tls_cipher_size_desc tls_cipher_size_desc[];
+#define TLS_CIPHER_MIN TLS_CIPHER_AES_GCM_128
+#define TLS_CIPHER_MAX TLS_CIPHER_ARIA_GCM_256
+extern const struct tls_cipher_size_desc tls_cipher_size_desc[TLS_CIPHER_MAX + 1 - TLS_CIPHER_MIN];
+
+static inline const struct tls_cipher_size_desc *get_cipher_size_desc(u16 cipher_type)
+{
+	if (cipher_type < TLS_CIPHER_MIN || cipher_type > TLS_CIPHER_MAX)
+		return NULL;
+
+	return &tls_cipher_size_desc[cipher_type - TLS_CIPHER_MIN];
+}
+
 
 /* TLS records are maintained in 'struct tls_rec'. It stores the memory pages
  * allocated or mapped for each TLS record. After encryption, the records are

net/tls/tls_device.c

@@ -898,7 +898,7 @@ tls_device_reencrypt(struct sock *sk, struct tls_context *tls_ctx)
 	default:
 		return -EINVAL;
 	}
-	cipher_sz = &tls_cipher_size_desc[tls_ctx->crypto_recv.info.cipher_type];
+	cipher_sz = get_cipher_size_desc(tls_ctx->crypto_recv.info.cipher_type);
 
 	rxm = strp_msg(tls_strp_msg(sw_ctx));
 	orig_buf = kmalloc(rxm->full_len + TLS_HEADER_SIZE + cipher_sz->iv,
@@ -1094,7 +1094,7 @@ int tls_set_device_offload(struct sock *sk, struct tls_context *ctx)
 		rc = -EINVAL;
 		goto release_netdev;
 	}
-	cipher_sz = &tls_cipher_size_desc[crypto_info->cipher_type];
+	cipher_sz = get_cipher_size_desc(crypto_info->cipher_type);
 
 	/* Sanity-check the rec_seq_size for stack allocations */
 	if (cipher_sz->rec_seq > TLS_MAX_REC_SEQ_SIZE) {

net/tls/tls_device_fallback.c

@@ -69,7 +69,7 @@ static int tls_enc_record(struct aead_request *aead_req,
 	default:
 		return -EINVAL;
 	}
-	cipher_sz = &tls_cipher_size_desc[prot->cipher_type];
+	cipher_sz = get_cipher_size_desc(prot->cipher_type);
 
 	buf_size = TLS_HEADER_SIZE + cipher_sz->iv;
 	len = min_t(int, *in_len, buf_size);
@@ -310,7 +310,7 @@ static void fill_sg_out(struct scatterlist sg_out[3], void *buf,
 			void *dummy_buf)
 {
 	const struct tls_cipher_size_desc *cipher_sz =
-		&tls_cipher_size_desc[tls_ctx->crypto_send.info.cipher_type];
+		get_cipher_size_desc(tls_ctx->crypto_send.info.cipher_type);
 
 	sg_set_buf(&sg_out[0], dummy_buf, sync_size);
 	sg_set_buf(&sg_out[1], nskb->data + tcp_payload_offset, payload_len);
@@ -348,7 +348,7 @@ static struct sk_buff *tls_enc_skb(struct tls_context *tls_ctx,
 	default:
 		goto free_req;
 	}
-	cipher_sz = &tls_cipher_size_desc[tls_ctx->crypto_send.info.cipher_type];
+	cipher_sz = get_cipher_size_desc(tls_ctx->crypto_send.info.cipher_type);
 	buf_len = cipher_sz->salt + cipher_sz->iv + TLS_AAD_SPACE_SIZE +
 		  sync_size + cipher_sz->tag;
 	buf = kmalloc(buf_len, GFP_ATOMIC);
@@ -495,7 +495,7 @@ int tls_sw_fallback_init(struct sock *sk,
 		rc = -EINVAL;
 		goto free_aead;
 	}
-	cipher_sz = &tls_cipher_size_desc[crypto_info->cipher_type];
+	cipher_sz = get_cipher_size_desc(crypto_info->cipher_type);
 
 	rc = crypto_aead_setkey(offload_ctx->aead_send, key, cipher_sz->key);
 	if (rc)

net/tls/tls_main.c

@@ -58,7 +58,7 @@ enum {
 	TLS_NUM_PROTS,
 };
 
-#define CIPHER_SIZE_DESC(cipher) [cipher] = { \
+#define CIPHER_SIZE_DESC(cipher) [cipher - TLS_CIPHER_MIN] = {	\
 	.iv = cipher ## _IV_SIZE, \
 	.key = cipher ## _KEY_SIZE, \
 	.salt = cipher ## _SALT_SIZE, \
@@ -66,7 +66,7 @@ enum {
 	.rec_seq = cipher ## _REC_SEQ_SIZE, \
 }
 
-const struct tls_cipher_size_desc tls_cipher_size_desc[] = {
+const struct tls_cipher_size_desc tls_cipher_size_desc[TLS_CIPHER_MAX + 1 - TLS_CIPHER_MIN] = {
 	CIPHER_SIZE_DESC(TLS_CIPHER_AES_GCM_128),
 	CIPHER_SIZE_DESC(TLS_CIPHER_AES_GCM_256),
 	CIPHER_SIZE_DESC(TLS_CIPHER_AES_CCM_128),