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>

diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
index 4ad657d8809730d8db975e699dc79696634f9d8a..8738deff26fadde6a6bf200972d0422193e4fdc9 100644 (file)
--- a/security/integrity/evm/evm_crypto.c
+++ b/security/integrity/evm/evm_crypto.c
@@ -27,26 +27,35 @@ static int evmkey_len = MAX_KEY_SIZE;
 
 struct crypto_shash *hmac_tfm;
 
+static DEFINE_MUTEX(mutex);
+
 static struct shash_desc *init_desc(void)
 {
        int rc;
        struct shash_desc *desc;
 
        if (hmac_tfm == NULL) {
+               mutex_lock(&mutex);
+               if (hmac_tfm)
+                       goto out;
                hmac_tfm = crypto_alloc_shash(evm_hmac, 0, CRYPTO_ALG_ASYNC);
                if (IS_ERR(hmac_tfm)) {
                        pr_err("Can not allocate %s (reason: %ld)\n",
                               evm_hmac, PTR_ERR(hmac_tfm));
                        rc = PTR_ERR(hmac_tfm);
                        hmac_tfm = NULL;
+                       mutex_unlock(&mutex);
                        return ERR_PTR(rc);
                }
                rc = crypto_shash_setkey(hmac_tfm, evmkey, evmkey_len);
                if (rc) {
                        crypto_free_shash(hmac_tfm);
                        hmac_tfm = NULL;
+                       mutex_unlock(&mutex);
                        return ERR_PTR(rc);
                }
+out:
+               mutex_unlock(&mutex);
        }
 
        desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(hmac_tfm),