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Date:   Wed, 11 Apr 2018 07:31:42 -0700
From:   Dave Watson <davejwatson@fb.com>
To:     Kees Cook <keescook@chromium.org>
CC:     <linux-kernel@vger.kernel.org>, <netdev@vger.kernel.org>,
        Ilya Lesokhin <ilyal@mellanox.com>,
        Aviad Yehezkel <aviadye@mellanox.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: Re: [PATCH] net/tls: Remove VLA usage
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On 04/10/18 05:52 PM, Kees Cook wrote:
> In the quest to remove VLAs from the kernel[1], this replaces the VLA
> size with the only possible size used in the code, and adds a mechanism
> to double-check future IV sizes.
> 
> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
> 
> Signed-off-by: Kees Cook <keescook@chromium.org>

Thanks

Acked-by: Dave Watson <davejwatson@fb.com>

> ---
>  net/tls/tls_sw.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
> index 4dc766b03f00..71e79597f940 100644
> --- a/net/tls/tls_sw.c
> +++ b/net/tls/tls_sw.c
> @@ -41,6 +41,8 @@
>  #include <net/strparser.h>
>  #include <net/tls.h>
>  
> +#define MAX_IV_SIZE	TLS_CIPHER_AES_GCM_128_IV_SIZE
> +
>  static int tls_do_decryption(struct sock *sk,
>  			     struct scatterlist *sgin,
>  			     struct scatterlist *sgout,
> @@ -673,7 +675,7 @@ static int decrypt_skb(struct sock *sk, struct sk_buff *skb,
>  {
>  	struct tls_context *tls_ctx = tls_get_ctx(sk);
>  	struct tls_sw_context *ctx = tls_sw_ctx(tls_ctx);
> -	char iv[TLS_CIPHER_AES_GCM_128_SALT_SIZE + tls_ctx->rx.iv_size];
> +	char iv[TLS_CIPHER_AES_GCM_128_SALT_SIZE + MAX_IV_SIZE];
>  	struct scatterlist sgin_arr[MAX_SKB_FRAGS + 2];
>  	struct scatterlist *sgin = &sgin_arr[0];
>  	struct strp_msg *rxm = strp_msg(skb);
> @@ -1094,6 +1096,12 @@ int tls_set_sw_offload(struct sock *sk, struct tls_context *ctx, int tx)
>  		goto free_priv;
>  	}
>  
> +	/* Sanity-check the IV size for stack allocations. */
> +	if (iv_size > MAX_IV_SIZE) {
> +		rc = -EINVAL;
> +		goto free_priv;
> +	}
> +
>  	cctx->prepend_size = TLS_HEADER_SIZE + nonce_size;
>  	cctx->tag_size = tag_size;
>  	cctx->overhead_size = cctx->prepend_size + cctx->tag_size;
> -- 
> 2.7.4
> 
> 
> -- 
> Kees Cook
> Pixel Security