[PATCH] crypto: ahash - Fix crypto_ahash_import with partial block data

[Herbert Xu]

On Thu, Nov 13, 2025 at 07:30:12PM +0530, T Pratham wrote:
>
> diff --git a/crypto/ahash.c b/crypto/ahash.c
> index dfb4f5476428f..9510bdeda51de 100644
> --- a/crypto/ahash.c
> +++ b/crypto/ahash.c
> @@ -674,10 +674,12 @@ int crypto_ahash_import(struct ahash_request *req, const void *in)
>         if (crypto_ahash_get_flags(tfm) & CRYPTO_TFM_NEED_KEY)
>                 return -ENOKEY;
>         if (crypto_ahash_block_only(tfm)) {
> +               unsigned int plen = crypto_ahash_blocksize(tfm) + 1;
>                 unsigned int reqsize = crypto_ahash_reqsize(tfm);
> +               unsigned int ss = crypto_ahash_statesize(tfm);
>                 u8 *buf = ahash_request_ctx(req);
>  
> -               buf[reqsize - 1] = 0;
> +               memcpy(buf + reqsize - plen, in + ss - plen, plen);
>         }
>         return crypto_ahash_alg(tfm)->import(req, in);
>  }
> 
> Is there any particular reason why import is like how it is currently? As per
> my understanding import should reverse whatever export is doing and vice-versa.

Thanks, you're right that this is broken.

The zeroing of the partial block buffer should be in import_core
instead of import.

---8<---
Restore the partial block buffer in crypto_ahash_import by copying
it.  Check whether the partial block buffer exceeds the maximum
size and return -EOVERFLOW if it does.

Zero the partial block buffer in crypto_ahash_import_core.

Reported-by: T Pratham <t-pratham@xxxxxx>
Fixes: 9d7a0ab1c753 ("crypto: ahash - Handle partial blocks in API")
Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>

diff --git a/crypto/ahash.c b/crypto/ahash.c
index dfb4f5476428..819b484a1a00 100644
--- a/crypto/ahash.c
+++ b/crypto/ahash.c
@@ -661,6 +661,12 @@ int crypto_ahash_import_core(struct ahash_request *req, const void *in)
 						in);
 	if (crypto_ahash_get_flags(tfm) & CRYPTO_TFM_NEED_KEY)
 		return -ENOKEY;
+	if (crypto_ahash_block_only(tfm)) {
+		unsigned int reqsize = crypto_ahash_reqsize(tfm);
+		u8 *buf = ahash_request_ctx(req);
+
+		buf[reqsize - 1] = 0;
+	}
 	return crypto_ahash_alg(tfm)->import_core(req, in);
 }
 EXPORT_SYMBOL_GPL(crypto_ahash_import_core);
@@ -674,10 +680,14 @@ int crypto_ahash_import(struct ahash_request *req, const void *in)
 	if (crypto_ahash_get_flags(tfm) & CRYPTO_TFM_NEED_KEY)
 		return -ENOKEY;
 	if (crypto_ahash_block_only(tfm)) {
+		unsigned int plen = crypto_ahash_blocksize(tfm) + 1;
 		unsigned int reqsize = crypto_ahash_reqsize(tfm);
+		unsigned int ss = crypto_ahash_statesize(tfm);
 		u8 *buf = ahash_request_ctx(req);
 
-		buf[reqsize - 1] = 0;
+		memcpy(buf + reqsize - plen, in + ss - plen, plen);
+		if (buf[reqsize - 1] >= plen)
+			return -EOVERFLOW;
 	}
 	return crypto_ahash_alg(tfm)->import(req, in);
 }
-- 
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt