Re: [PATCH v2] crypto: algif_skcipher - Require setkey before accept(2)

[Milan Broz <gmazyland@gmail.com>]

On 12/25/2015 08:40 AM, Herbert Xu wrote:
> Dmitry Vyukov <dvyukov@google.com> wrote:
>>
>> I am testing with your two patches:
>> crypto: algif_skcipher - Use new skcipher interface
>> crypto: algif_skcipher - Require setkey before accept(2)
>> on top of a88164345b81292b55a8d4829fdd35c8d611cd7d (Dec 23).
> 
> You sent the email to everyone on the original CC list except me.
> Please don't do that.
> 
>> Now the following program causes a bunch of use-after-frees and them
>> kills kernel:
> 
> Yes there is an obvious bug in the patch that Julia Lawall has
> responded to in another thread.  Here is a fixed version.
> 
> ---8<--
> Some cipher implementations will crash if you try to use them
> without calling setkey first.  This patch adds a check so that
> the accept(2) call will fail with -ENOKEY if setkey hasn't been
> done on the socket yet.


Hi Herbert,

this patch breaks userspace in cryptsetup...

We use algif_skcipher in cryptsetup (for years, even before
there was Stephan's library) and with this patch applied
I see fail in ALG_SET_IV call (patch from your git).

I can fix it upstream, but for thousands of installations it will
be broken (for LUKS there is a fallback, cor TrueCrypt compatible devices
it will be unusable. Also people who configured kernel crypto API as default
backend will have non-working cryptsetup).

Is it really thing for stable branch?

Milan

> 
> Cc: stable@vger.kernel.org
> Reported-by: Dmitry Vyukov <dvyukov@google.com>
> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
> 
> diff --git a/crypto/algif_skcipher.c b/crypto/algif_skcipher.c
> index 5c756b3..f4431bc 100644
> --- a/crypto/algif_skcipher.c
> +++ b/crypto/algif_skcipher.c
> @@ -31,6 +31,11 @@ struct skcipher_sg_list {
>  	struct scatterlist sg[0];
>  };
>  
> +struct skcipher_tfm {
> +	struct crypto_skcipher *skcipher;
> +	bool has_key;
> +};
> +
>  struct skcipher_ctx {
>  	struct list_head tsgl;
>  	struct af_alg_sgl rsgl;
> @@ -750,17 +755,41 @@ static struct proto_ops algif_skcipher_ops = {
>  
>  static void *skcipher_bind(const char *name, u32 type, u32 mask)
>  {
> -	return crypto_alloc_skcipher(name, type, mask);
> +	struct skcipher_tfm *tfm;
> +	struct crypto_skcipher *skcipher;
> +
> +	tfm = kzalloc(sizeof(*tfm), GFP_KERNEL);
> +	if (!tfm)
> +		return ERR_PTR(-ENOMEM);
> +
> +	skcipher = crypto_alloc_skcipher(name, type, mask);
> +	if (IS_ERR(skcipher)) {
> +		kfree(tfm);
> +		return ERR_CAST(skcipher);
> +	}
> +
> +	tfm->skcipher = skcipher;
> +
> +	return tfm;
>  }
>  
>  static void skcipher_release(void *private)
>  {
> -	crypto_free_skcipher(private);
> +	struct skcipher_tfm *tfm = private;
> +
> +	crypto_free_skcipher(tfm->skcipher);
> +	kfree(tfm);
>  }
>  
>  static int skcipher_setkey(void *private, const u8 *key, unsigned int keylen)
>  {
> -	return crypto_skcipher_setkey(private, key, keylen);
> +	struct skcipher_tfm *tfm = private;
> +	int err;
> +
> +	err = crypto_skcipher_setkey(tfm->skcipher, key, keylen);
> +	tfm->has_key = !err;
> +
> +	return err;
>  }
>  
>  static void skcipher_wait(struct sock *sk)
> @@ -792,20 +821,25 @@ static int skcipher_accept_parent(void *private, struct sock *sk)
>  {
>  	struct skcipher_ctx *ctx;
>  	struct alg_sock *ask = alg_sk(sk);
> -	unsigned int len = sizeof(*ctx) + crypto_skcipher_reqsize(private);
> +	struct skcipher_tfm *tfm = private;
> +	struct crypto_skcipher *skcipher = tfm->skcipher;
> +	unsigned int len = sizeof(*ctx) + crypto_skcipher_reqsize(skcipher);
> +
> +	if (!tfm->has_key)
> +		return -ENOKEY;
>  
>  	ctx = sock_kmalloc(sk, len, GFP_KERNEL);
>  	if (!ctx)
>  		return -ENOMEM;
>  
> -	ctx->iv = sock_kmalloc(sk, crypto_skcipher_ivsize(private),
> +	ctx->iv = sock_kmalloc(sk, crypto_skcipher_ivsize(skcipher),
>  			       GFP_KERNEL);
>  	if (!ctx->iv) {
>  		sock_kfree_s(sk, ctx, len);
>  		return -ENOMEM;
>  	}
>  
> -	memset(ctx->iv, 0, crypto_skcipher_ivsize(private));
> +	memset(ctx->iv, 0, crypto_skcipher_ivsize(skcipher));
>  
>  	INIT_LIST_HEAD(&ctx->tsgl);
>  	ctx->len = len;
> @@ -818,7 +852,7 @@ static int skcipher_accept_parent(void *private, struct sock *sk)
>  
>  	ask->private = ctx;
>  
> -	skcipher_request_set_tfm(&ctx->req, private);
> +	skcipher_request_set_tfm(&ctx->req, skcipher);
>  	skcipher_request_set_callback(&ctx->req, CRYPTO_TFM_REQ_MAY_BACKLOG,
>  				      af_alg_complete, &ctx->completion);
>  
>