[PATCH] crypto: ahash - Stop legacy tfms from using the set_virt fallback path

[Herbert Xu]

On Thu, Jun 12, 2025 at 10:54:39PM -0700, Eric Biggers wrote:
>
> Actually, crypto_ahash::base::fb is initialized if CRYPTO_ALG_NEED_FALLBACK,
> which many of the drivers already set.  Then crypto_ahash_update() calls
> ahash_do_req_chain() if the algorithm does *not* have
> CRYPTO_AHASH_ALG_BLOCK_ONLY set.  Which then exports the driver's custom state
> and tries to import it into the fallback.
> 
> As far as I can tell, it's just broken for most of the existing drivers.

This fallback path is only meant to be used for drivers that have
been converted.  But you're right there is a check missing in there.

Thanks,

---8<---
Ensure that drivers that have not been converted to the ahash API
do not use the ahash_request_set_virt fallback path as they cannot
use the software fallback.

Reported-by: Eric Biggers <ebiggers at kernel.org>
Fixes: 9d7a0ab1c753 ("crypto: ahash - Handle partial blocks in API")
Signed-off-by: Herbert Xu <herbert at gondor.apana.org.au>

diff --git a/crypto/ahash.c b/crypto/ahash.c
index e10bc2659ae4..992228a9f283 100644
--- a/crypto/ahash.c
+++ b/crypto/ahash.c
@@ -347,6 +347,9 @@ static int ahash_do_req_chain(struct ahash_request *req,
 	if (crypto_ahash_statesize(tfm) > HASH_MAX_STATESIZE)
 		return -ENOSYS;
 
+	if (crypto_hash_no_export_core(tfm))
+		return -ENOSYS;
+
 	{
 		u8 state[HASH_MAX_STATESIZE];
 
diff --git a/include/crypto/internal/hash.h b/include/crypto/internal/hash.h
index 0f85c543f80b..f052afa6e7b0 100644
--- a/include/crypto/internal/hash.h
+++ b/include/crypto/internal/hash.h
@@ -91,6 +91,12 @@ static inline bool crypto_hash_alg_needs_key(struct hash_alg_common *alg)
 		!(alg->base.cra_flags & CRYPTO_ALG_OPTIONAL_KEY);
 }
 
+static inline bool crypto_hash_no_export_core(struct crypto_ahash *tfm)
+{
+	return crypto_hash_alg_common(tfm)->base.cra_flags &
+	       CRYPTO_AHASH_ALG_NO_EXPORT_CORE;
+}
+
 int crypto_grab_ahash(struct crypto_ahash_spawn *spawn,
 		      struct crypto_instance *inst,
 		      const char *name, u32 type, u32 mask);
-- 
Email: Herbert Xu <herbert at gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt