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From:   Ignat Korchagin <ignat@cloudflare.com>
To:     Herbert Xu <herbert@gondor.apana.org.au>,
        "David S . Miller" <davem@davemloft.net>,
        linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     kernel-team@cloudflare.com, Ignat Korchagin <ignat@cloudflare.com>
Subject: [PATCH] crypto: akcipher - default implementations for setting private/public keys
Date:   Fri, 29 Jul 2022 17:59:54 +0100
Message-Id: <20220729165954.991-1-ignat@cloudflare.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Many akcipher implementations (like ECDSA) support only signature
verifications only, so they don't have all callbacks defined.

Commit 78a0324f4a53 ("crypto: akcipher - default implementations for
request callbacks") introduced default callbacks for sign/verify
operations, which just return an error code.

However, these are not enough, because before calling sign/verify the
caller would likely call set_priv_key/set_pub_key first on the
instantiated transform (as the in-kernel testmgr does). These functions do
not have default stubs, so the kernel crashes, when trying to set a
private key on an akcipher, which doesn't support signature generation.

I've noticed this, when trying to add a KAT vector for ECDSA signature to
the testmgr.

With this patch the testmgr returns an error in dmesg (as it should)
instead of crashing the kernel NULL ptr dereference.

Fixes: 78a0324f4a53 ("crypto: akcipher - default implementations for request callbacks")
Signed-off-by: Ignat Korchagin <ignat@cloudflare.com>
---
 crypto/akcipher.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/crypto/akcipher.c b/crypto/akcipher.c
index f866085c8a4a..fc4db0c6ca33 100644
--- a/crypto/akcipher.c
+++ b/crypto/akcipher.c
@@ -120,6 +120,12 @@ static int akcipher_default_op(struct akcipher_request *req)
 	return -ENOSYS;
 }

+static int akcipher_default_set_key(struct crypto_akcipher *tfm,
+				     const void *key, unsigned int keylen)
+{
+	return -ENOSYS;
+}
+
 int crypto_register_akcipher(struct akcipher_alg *alg)
 {
 	struct crypto_alg *base = &alg->base;
@@ -132,6 +138,10 @@ int crypto_register_akcipher(struct akcipher_alg *alg)
 		alg->encrypt = akcipher_default_op;
 	if (!alg->decrypt)
 		alg->decrypt = akcipher_default_op;
+	if (!alg->set_priv_key)
+		alg->set_priv_key = akcipher_default_set_key;
+	if (!alg->set_pub_key)
+		alg->set_pub_key = akcipher_default_set_key;

 	akcipher_prepare_alg(alg);
 	return crypto_register_alg(base);
--
2.36.1