Re: [PATCH] crypto: atmel: handle authenc requests without plaintext

[Herbert Xu]

On Tue, Sep 22, 2026 at 07:17:04AM +0200, Karl Mehltretter wrote:
> Authenc permits a nonempty associated-data string with no plaintext.  The
> Atmel driver accepts such a request, has SHA process the associated data,
> and then unconditionally asks AES DMA to transfer zero bytes.  The Atmel
> DMA engines reject the zero-length descriptor, so the valid request fails,
> normally with -ENOMEM.
> 
> Skip the AES transfer when textlen is zero and proceed directly to SHA
> finalization.
> 
> Once an HMAC transform has cached its inner and outer states, SHA can
> complete this path synchronously.  The forced ahash completion callback
> then invokes the AES finalizer through a void function and discards its
> return value.  This loses -EBADMSG for a mismatched tag and reports
> successful decryption.
> 
> For synchronous SHA completion, release the SHA device without invoking
> the ahash callback and call the AES finalizer directly.  Its result then
> propagates through the synchronous call chain.  Keep the existing callback
> path for asynchronous completion.
> 
> On a SAM9X75, the unpatched driver failed valid AAD-only requests and
> returned success for a bad tag after the transform had been used once. With
> this change, bad tags return -EBADMSG for both fresh and reused transforms.
> 
> Fixes: 89a82ef87e01 ("crypto: atmel-authenc - add support to authenc(hmac(shaX), Y(aes)) modes")
> Assisted-by: LLM
> Signed-off-by: Karl Mehltretter <kmehltretter@xxxxxxxxx>
> ---
>  drivers/crypto/atmel-aes.c |  2 ++
>  drivers/crypto/atmel-sha.c | 14 ++++++++++++++
>  2 files changed, 16 insertions(+)

Patch applied.  Thanks.
-- 
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
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