Re: [PATCH] net/tls: Remove VLA usage

[David Miller]

From: Kees Cook 
Date: Tue, 10 Apr 2018 17:52:34 -0700

> 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=qpxydaacu1rq...@mail.gmail.com
> 
> Signed-off-by: Kees Cook 

Applied.

Re: [PATCH] net/tls: Remove VLA usage

[Dave Watson]

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=qpxydaacu1rq...@mail.gmail.com
> 
> Signed-off-by: Kees Cook 

Thanks

Acked-by: Dave Watson 

> ---
>  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 
>  #include 
>  
> +#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 = _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