Re: [PATCH] crypto: essiv: avoid request access after subrequest

[Ard Biesheuvel]

On Mon, 21 Sep 2026, at 11:04, Jiale Yao wrote:
> essiv_aead_crypt() reads rctx->assoc after submitting the child AEAD
> request. An asynchronous completion can run essiv_aead_done(), free the
> association buffer, and complete the outer request before the submission
> call returns. The later request-context access can therefore use freed
> memory and trigger a second free.
>
> Snapshot the association buffer pointer before submitting the child
> request and use the local value for synchronous cleanup.
>
> Fixes: be1eb7f78aa8 ("crypto: essiv - create wrapper template for ESSIV 
> generation")
>
> Signed-off-by: Jiale Yao <yaojiale02@xxxxxxx>
> ---
>  crypto/essiv.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/crypto/essiv.c b/crypto/essiv.c
> index a47a3eab6935..5aea4584d5cb 100644
> --- a/crypto/essiv.c
> +++ b/crypto/essiv.c
> @@ -189,6 +189,7 @@ static int essiv_aead_crypt(struct aead_request 
> *req, bool enc)
>  	int ivsize = crypto_aead_ivsize(tfm);
>  	int ssize = req->assoclen - ivsize;
>  	struct scatterlist *src = req->src;
> +	void *assoc;
>  	int err;
> 
>  	if (ssize < 0)
> @@ -247,11 +248,12 @@ static int essiv_aead_crypt(struct aead_request 
> *req, bool enc)
>  				  essiv_aead_done, req);
>  	aead_request_set_crypt(subreq, src, req->dst, req->cryptlen, req->iv);
> 
> +	assoc = rctx->assoc;
>  	err = enc ? crypto_aead_encrypt(subreq) :
>  		    crypto_aead_decrypt(subreq);
> 
> -	if (rctx->assoc && err != -EINPROGRESS && err != -EBUSY)
> -		kfree(rctx->assoc);
> +	if (assoc && err != -EINPROGRESS && err != -EBUSY)
> +		kfree(assoc);
>  	return err;
>  }
> 

The problem here seems to be that rctx is dereferenced before the comparison
of err. Just drop it completely from the if: kfree() ignores NULL pointers
anyway.