tls: rx: always allocate max possible aad size for decrypt

AAD size is either 5 or 13. Really no point complicating
the code for the 8B of difference. This will also let us
turn the chunked up buffer into a sane struct.
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/tls.h

@@ -66,6 +66,7 @@
 #define MAX_IV_SIZE			16
 #define TLS_TAG_SIZE			16
 #define TLS_MAX_REC_SEQ_SIZE		8
+#define TLS_MAX_AAD_SIZE		TLS_AAD_SPACE_SIZE
 
 /* For CCM mode, the full 16-bytes of IV is made of '4' fields of given sizes.
  *

net/tls/tls_sw.c

@@ -1450,7 +1450,7 @@ static int decrypt_internal(struct sock *sk, struct sk_buff *skb,
 
 	aead_size = sizeof(*aead_req) + crypto_aead_reqsize(ctx->aead_recv);
 	mem_size = aead_size + (nsg * sizeof(struct scatterlist));
-	mem_size = mem_size + prot->aad_size;
+	mem_size = mem_size + TLS_MAX_AAD_SIZE;
 	mem_size = mem_size + MAX_IV_SIZE;
 	mem_size = mem_size + prot->tail_size;
 
@@ -1467,7 +1467,7 @@ static int decrypt_internal(struct sock *sk, struct sk_buff *skb,
 	sgin = (struct scatterlist *)(mem + aead_size);
 	sgout = sgin + n_sgin;
 	aad = (u8 *)(sgout + n_sgout);
-	iv = aad + prot->aad_size;
+	iv = aad + TLS_MAX_AAD_SIZE;
 	tail = iv + MAX_IV_SIZE;
 
 	/* For CCM based ciphers, first byte of nonce+iv is a constant */
@@ -2474,13 +2474,6 @@ int tls_set_sw_offload(struct sock *sk, struct tls_context *ctx, int tx)
 		goto free_priv;
 	}
 
-	/* Sanity-check the sizes for stack allocations. */
-	if (iv_size > MAX_IV_SIZE || nonce_size > MAX_IV_SIZE ||
-	    rec_seq_size > TLS_MAX_REC_SEQ_SIZE || tag_size != TLS_TAG_SIZE) {
-		rc = -EINVAL;
-		goto free_priv;
-	}
-
 	if (crypto_info->version == TLS_1_3_VERSION) {
 		nonce_size = 0;
 		prot->aad_size = TLS_HEADER_SIZE;
@@ -2490,6 +2483,14 @@ int tls_set_sw_offload(struct sock *sk, struct tls_context *ctx, int tx)
 		prot->tail_size = 0;
 	}
 
+	/* Sanity-check the sizes for stack allocations. */
+	if (iv_size > MAX_IV_SIZE || nonce_size > MAX_IV_SIZE ||
+	    rec_seq_size > TLS_MAX_REC_SEQ_SIZE || tag_size != TLS_TAG_SIZE ||
+	    prot->aad_size > TLS_MAX_AAD_SIZE) {
+		rc = -EINVAL;
+		goto free_priv;
+	}
+
 	prot->version = crypto_info->version;
 	prot->cipher_type = crypto_info->cipher_type;
 	prot->prepend_size = TLS_HEADER_SIZE + nonce_size;