[RFC PATCH 01/30] crypto: des/3des_ede - add new helpers to verify key length

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

The recently added helper routines to perform key strength validation
of 3ede_keys is slightly inadequate, since it doesn't check the key
length, and it comes in two versions, neither of which are highly
useful for anything other than skciphers (and many users still use the
older blkcipher interfaces).

So let's add a new helper and, considering that this is a helper function
that is only intended to be used by crypto code itself, put it in a new
des.h header under crypto/internal.

While at it, implement a similar helper for single DES, so that we can
replace the pattern of calling des_ekey() into a temp buffer that occurs
in many drivers in drivers/crypto.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
 crypto/des_generic.c          | 13 ---
 include/crypto/internal/des.h | 85 ++++++++++++++++++++
 2 files changed, 85 insertions(+), 13 deletions(-)

diff --git a/crypto/des_generic.c b/crypto/des_generic.c
index d7a88b4fa611..c94a303da4dd 100644
--- a/crypto/des_generic.c
+++ b/crypto/des_generic.c
@@ -846,19 +846,6 @@ static void des_decrypt(struct crypto_tfm *tfm, u8 *dst, const u8 *src)
 	d[1] = cpu_to_le32(L);
 }
 
-/*
- * RFC2451:
- *
- *   For DES-EDE3, there is no known need to reject weak or
- *   complementation keys.  Any weakness is obviated by the use of
- *   multiple keys.
- *
- *   However, if the first two or last two independent 64-bit keys are
- *   equal (k1 == k2 or k2 == k3), then the DES3 operation is simply the
- *   same as DES.  Implementers MUST reject keys that exhibit this
- *   property.
- *
- */
 int __des3_ede_setkey(u32 *expkey, u32 *flags, const u8 *key,
 		      unsigned int keylen)
 {
diff --git a/include/crypto/internal/des.h b/include/crypto/internal/des.h
new file mode 100644
index 000000000000..e33b32c496cd
--- /dev/null
+++ b/include/crypto/internal/des.h
@@ -0,0 +1,85 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * DES & Triple DES EDE key verification helpers
+ */
+
+#ifndef __CRYPTO_INTERNAL_DES_H
+#define __CRYPTO_INTERNAL_DES_H
+
+#include <linux/crypto.h>
+#include <linux/fips.h>
+#include <crypto/des.h>
+
+static inline int crypto_des_verify_key(struct crypto_tfm *tfm, const u8 *key,
+					unsigned int key_len)
+{
+	u32 tmp[DES_EXPKEY_WORDS];
+	int err = -EINVAL;
+
+	if (key_len != DES_KEY_SIZE) {
+		crypto_tfm_set_flags(tfm, CRYPTO_TFM_RES_BAD_KEY_LEN);
+		return -EINVAL;
+	}
+
+	if (!des_ekey(tmp, key) &&
+	    (fips_enabled || (crypto_tfm_get_flags(tfm) &
+			      CRYPTO_TFM_REQ_FORBID_WEAK_KEYS)))
+		goto bad;
+
+	err = 0;
+out:
+	memzero_explicit(tmp, sizeof(tmp));
+	return err;
+
+bad:
+	crypto_tfm_set_flags(tfm, CRYPTO_TFM_RES_WEAK_KEY);
+	goto out;
+}
+
+/*
+ * RFC2451:
+ *
+ *   For DES-EDE3, there is no known need to reject weak or
+ *   complementation keys.  Any weakness is obviated by the use of
+ *   multiple keys.
+ *
+ *   However, if the first two or last two independent 64-bit keys are
+ *   equal (k1 == k2 or k2 == k3), then the DES3 operation is simply the
+ *   same as DES.  Implementers MUST reject keys that exhibit this
+ *   property.
+ *
+ */
+static inline int crypto_des3_ede_verify_key(struct crypto_tfm *tfm,
+					     const u8 *key,
+					     unsigned int key_len)
+{
+	int err = -EINVAL;
+	u32 K[6];
+
+	if (key_len != DES3_EDE_KEY_SIZE) {
+		crypto_tfm_set_flags(tfm, CRYPTO_TFM_RES_BAD_KEY_LEN);
+		return -EINVAL;
+	}
+
+	memcpy(K, key, DES3_EDE_KEY_SIZE);
+
+	if ((!((K[0] ^ K[2]) | (K[1] ^ K[3])) ||
+	     !((K[2] ^ K[4]) | (K[3] ^ K[5]))) &&
+	    (fips_enabled || (crypto_tfm_get_flags(tfm) &
+		              CRYPTO_TFM_REQ_FORBID_WEAK_KEYS)))
+		goto bad;
+
+	if ((!((K[0] ^ K[4]) | (K[1] ^ K[5]))) && fips_enabled)
+		goto bad;
+
+	err = 0;
+out:
+	memzero_explicit(K, DES3_EDE_KEY_SIZE);
+	return err;
+
+bad:
+	crypto_tfm_set_flags(tfm, CRYPTO_TFM_RES_WEAK_KEY);
+	goto out;
+}
+
+#endif /* __CRYPTO_INTERNAL_DES_H */
-- 
2.20.1