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From: Eric Biggers <ebiggers@kernel.org>
To: stable@vger.kernel.org
Cc: linux-crypto@vger.kernel.org
Subject: [PATCH 4.4 2/2] crypto: gcm - fix incompatibility between "gcm" and "gcm_base"
Date: Fri, 17 May 2019 11:06:10 -0700
Message-ID: <20190517180610.150453-2-ebiggers@kernel.org> (raw)
In-Reply-To: <20190517180610.150453-1-ebiggers@kernel.org>

From: Eric Biggers <ebiggers@google.com>

commit f699594d436960160f6d5ba84ed4a222f20d11cd upstream.
[Please apply to 4.4-stable.]

GCM instances can be created by either the "gcm" template, which only
allows choosing the block cipher, e.g. "gcm(aes)"; or by "gcm_base",
which allows choosing the ctr and ghash implementations, e.g.
"gcm_base(ctr(aes-generic),ghash-generic)".

However, a "gcm_base" instance prevents a "gcm" instance from being
registered using the same implementations.  Nor will the instance be
found by lookups of "gcm".  This can be used as a denial of service.
Moreover, "gcm_base" instances are never tested by the crypto
self-tests, even if there are compatible "gcm" tests.

The root cause of these problems is that instances of the two templates
use different cra_names.  Therefore, fix these problems by making
"gcm_base" instances set the same cra_name as "gcm" instances, e.g.
"gcm(aes)" instead of "gcm_base(ctr(aes-generic),ghash-generic)".

This requires extracting the block cipher name from the name of the ctr
algorithm.  It also requires starting to verify that the algorithms are
really ctr and ghash, not something else entirely.  But it would be
bizarre if anyone were actually using non-gcm-compatible algorithms with
gcm_base, so this shouldn't break anyone in practice.

Fixes: d00aa19b507b ("[CRYPTO] gcm: Allow block cipher parameter")
Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
---
 crypto/gcm.c | 34 +++++++++++-----------------------
 1 file changed, 11 insertions(+), 23 deletions(-)

diff --git a/crypto/gcm.c b/crypto/gcm.c
index f1c16589af8bb..9d3bffc0238f0 100644
--- a/crypto/gcm.c
+++ b/crypto/gcm.c
@@ -616,7 +616,6 @@ static void crypto_gcm_free(struct aead_instance *inst)
 
 static int crypto_gcm_create_common(struct crypto_template *tmpl,
 				    struct rtattr **tb,
-				    const char *full_name,
 				    const char *ctr_name,
 				    const char *ghash_name)
 {
@@ -657,7 +656,8 @@ static int crypto_gcm_create_common(struct crypto_template *tmpl,
 		goto err_free_inst;
 
 	err = -EINVAL;
-	if (ghash->digestsize != 16)
+	if (strcmp(ghash->base.cra_name, "ghash") != 0 ||
+	    ghash->digestsize != 16)
 		goto err_drop_ghash;
 
 	crypto_set_skcipher_spawn(&ctx->ctr, aead_crypto_instance(inst));
@@ -669,24 +669,24 @@ static int crypto_gcm_create_common(struct crypto_template *tmpl,
 
 	ctr = crypto_skcipher_spawn_alg(&ctx->ctr);
 
-	/* We only support 16-byte blocks. */
+	/* The skcipher algorithm must be CTR mode, using 16-byte blocks. */
 	err = -EINVAL;
-	if (ctr->cra_ablkcipher.ivsize != 16)
+	if (strncmp(ctr->cra_name, "ctr(", 4) != 0 ||
+	    ctr->cra_ablkcipher.ivsize != 16 ||
+	    ctr->cra_blocksize != 1)
 		goto out_put_ctr;
 
-	/* Not a stream cipher? */
-	if (ctr->cra_blocksize != 1)
+	err = -ENAMETOOLONG;
+	if (snprintf(inst->alg.base.cra_name, CRYPTO_MAX_ALG_NAME,
+		     "gcm(%s", ctr->cra_name + 4) >= CRYPTO_MAX_ALG_NAME)
 		goto out_put_ctr;
 
-	err = -ENAMETOOLONG;
 	if (snprintf(inst->alg.base.cra_driver_name, CRYPTO_MAX_ALG_NAME,
 		     "gcm_base(%s,%s)", ctr->cra_driver_name,
 		     ghash_alg->cra_driver_name) >=
 	    CRYPTO_MAX_ALG_NAME)
 		goto out_put_ctr;
 
-	memcpy(inst->alg.base.cra_name, full_name, CRYPTO_MAX_ALG_NAME);
-
 	inst->alg.base.cra_flags = (ghash->base.cra_flags | ctr->cra_flags) &
 				   CRYPTO_ALG_ASYNC;
 	inst->alg.base.cra_priority = (ghash->base.cra_priority +
@@ -727,7 +727,6 @@ static int crypto_gcm_create(struct crypto_template *tmpl, struct rtattr **tb)
 {
 	const char *cipher_name;
 	char ctr_name[CRYPTO_MAX_ALG_NAME];
-	char full_name[CRYPTO_MAX_ALG_NAME];
 
 	cipher_name = crypto_attr_alg_name(tb[1]);
 	if (IS_ERR(cipher_name))
@@ -737,12 +736,7 @@ static int crypto_gcm_create(struct crypto_template *tmpl, struct rtattr **tb)
 	    CRYPTO_MAX_ALG_NAME)
 		return -ENAMETOOLONG;
 
-	if (snprintf(full_name, CRYPTO_MAX_ALG_NAME, "gcm(%s)", cipher_name) >=
-	    CRYPTO_MAX_ALG_NAME)
-		return -ENAMETOOLONG;
-
-	return crypto_gcm_create_common(tmpl, tb, full_name,
-					ctr_name, "ghash");
+	return crypto_gcm_create_common(tmpl, tb, ctr_name, "ghash");
 }
 
 static struct crypto_template crypto_gcm_tmpl = {
@@ -756,7 +750,6 @@ static int crypto_gcm_base_create(struct crypto_template *tmpl,
 {
 	const char *ctr_name;
 	const char *ghash_name;
-	char full_name[CRYPTO_MAX_ALG_NAME];
 
 	ctr_name = crypto_attr_alg_name(tb[1]);
 	if (IS_ERR(ctr_name))
@@ -766,12 +759,7 @@ static int crypto_gcm_base_create(struct crypto_template *tmpl,
 	if (IS_ERR(ghash_name))
 		return PTR_ERR(ghash_name);
 
-	if (snprintf(full_name, CRYPTO_MAX_ALG_NAME, "gcm_base(%s,%s)",
-		     ctr_name, ghash_name) >= CRYPTO_MAX_ALG_NAME)
-		return -ENAMETOOLONG;
-
-	return crypto_gcm_create_common(tmpl, tb, full_name,
-					ctr_name, ghash_name);
+	return crypto_gcm_create_common(tmpl, tb, ctr_name, ghash_name);
 }
 
 static struct crypto_template crypto_gcm_base_tmpl = {
-- 
2.21.0.1020.gf2820cf01a-goog


  reply index

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-17 18:06 [PATCH 4.4 1/2] crypto: gcm - Fix error return code in crypto_gcm_create_common() Eric Biggers
2019-05-17 18:06 ` Eric Biggers [this message]
2019-05-18  6:56   ` [PATCH 4.4 2/2] crypto: gcm - fix incompatibility between "gcm" and "gcm_base" Greg KH

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