CVE-2017-9211: NULL Pointer Dereference (CWE-476)
value: The crypto_skcipher_init_tfm function in crypto/skcipher.c in the Linux kernel through 4.11.2 relies on a setkey function that lacks a key-size check, which allows local users to cause a denial of service (NULL pointer dereference) via a crafted application.
CWE description: The product dereferences a pointer that it expects to be valid but is NULL.
CVSS v3 base score: 5.5
Published: 2017-05-23T05:29Z
Repository: https://github.com/torvalds/linux
Language: C
Files changed: crypto/skcipher.c
Commit date: 2017-05-18 13:04:05 +0800
Commit message: crypto: skcipher - Add missing API setkey checks

The API setkey checks for key sizes and alignment went AWOL during the
skcipher conversion.  This patch restores them.

Cc: <stable@vger.kernel.org>
Fixes: 4e6c3df4d729 ("crypto: skcipher - Add low-level skcipher...")
Reported-by: Baozeng <sploving1@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Diff: diff --git a/crypto/skcipher.c b/crypto/skcipher.c
index 014af741fc6a..4faa0fd53b0c 100644
--- a/crypto/skcipher.c
+++ b/crypto/skcipher.c
@@ -762,10 +762,48 @@ static int crypto_init_skcipher_ops_ablkcipher(struct crypto_tfm *tfm)
 	skcipher->keysize = calg->cra_ablkcipher.max_keysize;
 
 	return 0;
 }
 
+static int skcipher_setkey_unaligned(struct crypto_skcipher *tfm,
+				     const u8 *key, unsigned int keylen)
+{
+	unsigned long alignmask = crypto_skcipher_alignmask(tfm);
+	struct skcipher_alg *cipher = crypto_skcipher_alg(tfm);
+	u8 *buffer, *alignbuffer;
+	unsigned long absize;
+	int ret;
+
+	absize = keylen + alignmask;
+	buffer = kmalloc(absize, GFP_ATOMIC);
+	if (!buffer)
+		return -ENOMEM;
+
+	alignbuffer = (u8 *)ALIGN((unsigned long)buffer, alignmask + 1);
+	memcpy(alignbuffer, key, keylen);
+	ret = cipher->setkey(tfm, alignbuffer, keylen);
+	kzfree(buffer);
+	return ret;
+}
+
+static int skcipher_setkey(struct crypto_skcipher *tfm, const u8 *key,
+			   unsigned int keylen)
+{
+	struct skcipher_alg *cipher = crypto_skcipher_alg(tfm);
+	unsigned long alignmask = crypto_skcipher_alignmask(tfm);
+
+	if (keylen < cipher->min_keysize || keylen > cipher->max_keysize) {
+		crypto_skcipher_set_flags(tfm, CRYPTO_TFM_RES_BAD_KEY_LEN);
+		return -EINVAL;
+	}
+
+	if ((unsigned long)key & alignmask)
+		return skcipher_setkey_unaligned(tfm, key, keylen);
+
+	return cipher->setkey(tfm, key, keylen);
+}
+
 static void crypto_skcipher_exit_tfm(struct crypto_tfm *tfm)
 {
 	struct crypto_skcipher *skcipher = __crypto_skcipher_cast(tfm);
 	struct skcipher_alg *alg = crypto_skcipher_alg(skcipher);
 
@@ -782,11 +820,11 @@ static int crypto_skcipher_init_tfm(struct crypto_tfm *tfm)
 
 	if (tfm->__crt_alg->cra_type == &crypto_ablkcipher_type ||
 	    tfm->__crt_alg->cra_type == &crypto_givcipher_type)
 		return crypto_init_skcipher_ops_ablkcipher(tfm);
 
-	skcipher->setkey = alg->setkey;
+	skcipher->setkey = skcipher_setkey;
 	skcipher->encrypt = alg->encrypt;
 	skcipher->decrypt = alg->decrypt;
 	skcipher->ivsize = alg->ivsize;
 	skcipher->keysize = alg->max_keysize;
 

Vulnerable code: 	skcipher->setkey = alg->setkey;
Fixed code: static int skcipher_setkey_unaligned(struct crypto_skcipher *tfm,
				     const u8 *key, unsigned int keylen)
{
	unsigned long alignmask = crypto_skcipher_alignmask(tfm);
	struct skcipher_alg *cipher = crypto_skcipher_alg(tfm);
	u8 *buffer, *alignbuffer;
	unsigned long absize;
	int ret;

	absize = keylen + alignmask;
	buffer = kmalloc(absize, GFP_ATOMIC);
	if (!buffer)
		return -ENOMEM;

	alignbuffer = (u8 *)ALIGN((unsigned long)buffer, alignmask + 1);
	memcpy(alignbuffer, key, keylen);
	ret = cipher->setkey(tfm, alignbuffer, keylen);
	kzfree(buffer);
	return ret;
}

static int skcipher_setkey(struct crypto_skcipher *tfm, const u8 *key,
			   unsigned int keylen)
{
	struct skcipher_alg *cipher = crypto_skcipher_alg(tfm);
	unsigned long alignmask = crypto_skcipher_alignmask(tfm);

	if (keylen < cipher->min_keysize || keylen > cipher->max_keysize) {
		crypto_skcipher_set_flags(tfm, CRYPTO_TFM_RES_BAD_KEY_LEN);
		return -EINVAL;
	}

	if ((unsigned long)key & alignmask)
		return skcipher_setkey_unaligned(tfm, key, keylen);

	return cipher->setkey(tfm, key, keylen);
}

	skcipher->setkey = skcipher_setkey;