KEYS: trusted: dcp: fix improper sg use with CONFIG_VMAP_STACK=y

With vmalloc stack addresses enabled (CONFIG_VMAP_STACK=y) DCP trusted
keys can crash during en- and decryption of the blob encryption key via
the DCP crypto driver. This is caused by improperly using sg_init_one()
with vmalloc'd stack buffers (plain_key_blob).

Fix this by always using kmalloc() for buffers we give to the DCP crypto
driver.

Cc: stable@vger.kernel.org # v6.10+
Fixes: 0e28bf6 ("KEYS: trusted: dcp: fix leak of blob encryption key")
Signed-off-by: David Gstir <david@sigma-star.at>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

Author: iokill

security/keys/trusted-keys/trusted_dcp.c

@@ -201,12 +201,16 @@ static int trusted_dcp_seal(struct trusted_key_payload *p, char *datablob)
 {
 	struct dcp_blob_fmt *b = (struct dcp_blob_fmt *)p->blob;
 	int blen, ret;
-	u8 plain_blob_key[AES_KEYSIZE_128];
+	u8 *plain_blob_key;
 
 	blen = calc_blob_len(p->key_len);
 	if (blen > MAX_BLOB_SIZE)
 		return -E2BIG;
 
+	plain_blob_key = kmalloc(AES_KEYSIZE_128, GFP_KERNEL);
+	if (!plain_blob_key)
+		return -ENOMEM;
+
 	b->fmt_version = DCP_BLOB_VERSION;
 	get_random_bytes(b->nonce, AES_KEYSIZE_128);
 	get_random_bytes(plain_blob_key, AES_KEYSIZE_128);
@@ -229,7 +233,8 @@ static int trusted_dcp_seal(struct trusted_key_payload *p, char *datablob)
 	ret = 0;
 
 out:
-	memzero_explicit(plain_blob_key, sizeof(plain_blob_key));
+	memzero_explicit(plain_blob_key, AES_KEYSIZE_128);
+	kfree(plain_blob_key);
 
 	return ret;
 }
@@ -238,7 +243,7 @@ static int trusted_dcp_unseal(struct trusted_key_payload *p, char *datablob)
 {
 	struct dcp_blob_fmt *b = (struct dcp_blob_fmt *)p->blob;
 	int blen, ret;
-	u8 plain_blob_key[AES_KEYSIZE_128];
+	u8 *plain_blob_key = NULL;
 
 	if (b->fmt_version != DCP_BLOB_VERSION) {
 		pr_err("DCP blob has bad version: %i, expected %i\n",
@@ -256,6 +261,12 @@ static int trusted_dcp_unseal(struct trusted_key_payload *p, char *datablob)
 		goto out;
 	}
 
+	plain_blob_key = kmalloc(AES_KEYSIZE_128, GFP_KERNEL);
+	if (!plain_blob_key) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
 	ret = decrypt_blob_key(b->blob_key, plain_blob_key);
 	if (ret) {
 		pr_err("Unable to decrypt blob key: %i\n", ret);
@@ -271,7 +282,10 @@ static int trusted_dcp_unseal(struct trusted_key_payload *p, char *datablob)
 
 	ret = 0;
 out:
-	memzero_explicit(plain_blob_key, sizeof(plain_blob_key));
+	if (plain_blob_key) {
+		memzero_explicit(plain_blob_key, AES_KEYSIZE_128);
+		kfree(plain_blob_key);
+	}
 
 	return ret;
 }