evm: prevent racing during tfm allocation

There is a small chance of racing during tfm allocation.
This patch fixes it.

Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>
Acked-by: Mimi Zohar <zohar@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>

1 files changed, 11 insertions, 3 deletions

diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
index 3b9f5a080e4f..f1d4ad0cea2c 100644
--- a/security/integrity/evm/evm_crypto.c
+++ b/security/integrity/evm/evm_crypto.c
@@ -28,9 +28,11 @@ static int evmkey_len = MAX_KEY_SIZE;
 struct crypto_shash *hmac_tfm;
 struct crypto_shash *hash_tfm;
 
+static DEFINE_MUTEX(mutex);
+
 static struct shash_desc *init_desc(const char type)
 {
-        int rc;
+        long rc;
         char *algo;
         struct crypto_shash **tfm;
         struct shash_desc *desc;
@@ -44,12 +46,15 @@ static struct shash_desc *init_desc(const char type)
         }
 
         if (*tfm == NULL) {
+                mutex_lock(&mutex);
+                if (*tfm)
+                        goto out;
                 *tfm = crypto_alloc_shash(algo, 0, CRYPTO_ALG_ASYNC);
                 if (IS_ERR(*tfm)) {
-                        pr_err("Can not allocate %s (reason: %ld)\n",
-                               algo, PTR_ERR(*tfm));
                         rc = PTR_ERR(*tfm);
+                        pr_err("Can not allocate %s (reason: %ld)\n", algo, rc);
                         *tfm = NULL;
+                        mutex_unlock(&mutex);
                         return ERR_PTR(rc);
                 }
                 if (type == EVM_XATTR_HMAC) {
@@ -57,9 +62,12 @@ static struct shash_desc *init_desc(const char type)
                         if (rc) {
                                 crypto_free_shash(*tfm);
                                 *tfm = NULL;
+                                mutex_unlock(&mutex);
                                 return ERR_PTR(rc);
                         }
                 }
+out:
+                mutex_unlock(&mutex);
         }
 
         desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm),