Re: [PATCH] crypto: virtio - bound the device-reported akcipher result

[Michael S. Tsirkin]

On Sat, Jun 20, 2026 at 09:44:21PM -0500, Bryam Vargas via B4 Relay wrote:
> From: Bryam Vargas <hexlabsecurity@xxxxxxxxx>
> 
> length


some kind of corruption here.

> virtio_crypto_dataq_akcipher_callback() sets the result length from the
> device-reported response length without bounding it to the destination
> buffer, which was allocated for the original request length.
> sg_copy_from_buffer() then reads that many bytes from the destination
> buffer; a backend reporting a larger length over-reads adjacent kernel
> heap into the caller's scatterlist (an out-of-bounds read).
> 
> Clamp the reported length to the originally requested destination length.
> A conforming device reports no more than that, so valid results are
> unaffected.
> 
> Fixes: a36bd0ad9fbf ("virtio-crypto: adjust dst_len at ops callback")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Bryam Vargas <hexlabsecurity@xxxxxxxxx>
> ---
>  drivers/crypto/virtio/virtio_crypto_akcipher_algs.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/crypto/virtio/virtio_crypto_akcipher_algs.c b/drivers/crypto/virtio/virtio_crypto_akcipher_algs.c
> index d8d452cac391..64ea141f018c 100644
> --- a/drivers/crypto/virtio/virtio_crypto_akcipher_algs.c
> +++ b/drivers/crypto/virtio/virtio_crypto_akcipher_algs.c
> @@ -88,7 +88,8 @@ static void virtio_crypto_dataq_akcipher_callback(struct virtio_crypto_request *
>  	}
>  
>  	/* actual length may be less than dst buffer */
> -	akcipher_req->dst_len = len - sizeof(vc_req->status);
> +	akcipher_req->dst_len = min_t(unsigned int, len - sizeof(vc_req->status),
> +				      akcipher_req->dst_len);
>  	sg_copy_from_buffer(akcipher_req->dst, sg_nents(akcipher_req->dst),
>  			    vc_akcipher_req->dst_buf, akcipher_req->dst_len);
>  	virtio_crypto_akcipher_finalize_req(vc_akcipher_req, akcipher_req, error);
> 
> ---
> base-commit: 1a3746ccbb0a97bed3c06ccde6b880013b1dddc1
> change-id: 20260620-b4-disp-27caeeac-5b8b67962fdd
> 
> Best regards,
> -- 
> Bryam Vargas <hexlabsecurity@xxxxxxxxx>
>