CVE-2017-9211 (published 2017-05-23T05:29Z)

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.

Severity: MEDIUM
CVSS v2 base score: 4.9 (AV:L/AC:L/Au:N/C:N/I:N/A:C)
CVSS v3 base score: 5.5, MEDIUM (CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H)

Weakness information:
cwe_id: CWE-476
cwe_name: NULL Pointer Dereference
description: The product dereferences a pointer that it expects to be valid but is NULL.
extended_description: 
            
            
            
         
         

Fix information:
repo_url: https://github.com/torvalds/linux
commit_details: repo_url: https://github.com/torvalds/linux
author: Herbert Xu
author_date: 2017-05-10 03:48:23+08:00
msg: 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>
repository: repo_url: https://github.com/torvalds/linux
repo_name: torvalds/linux
description: Linux kernel source tree
repo_language: C
owner: torvalds
file_changes: filename: skcipher.c
change_type: ModificationType.MODIFY
diff: @@ -764,6 +764,44 @@ static int crypto_init_skcipher_ops_ablkcipher(struct crypto_tfm *tfm)
 	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);
@@ -784,7 +822,7 @@ static int crypto_skcipher_init_tfm(struct crypto_tfm *tfm)
 	    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;

programming_language: C