storage: protect TA directory with a mutex

There is a race condition in the code that creates and deletes trusted
storage. If multiple threads invoke a multi-session TA to create and
delete different files (such as xtest 6016), the following can occur:

    Thread #1 (create file #1) |   Thread #2 (delete file #2)
                               |
                               |   remove("/TA_dir/file");
    mkdir("/TA_dir");          |
                               |   rmdir("/TA_dir");
    create("/TA_dir/file1");   |
      => ENOENT                |

Add a mutex to prevent this race condition.

Note: the bug is currently not triggered by xtest 1016 because the test
is run for RPMB FS only, and because directory operations are no-ops in
the RPMB implementation. The fix will be needed when enabling single-TA
concurrency with the REE and SQL backends.

Signed-off-by: Jerome Forissier <[email protected]>

core/tee/tee_svc_storage.c

@@ -25,6 +25,7 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include <kernel/mutex.h>
 #include <kernel/tee_ta_manager.h>
 #include <kernel/tee_misc.h>
 #include <mm/tee_mmu.h>
@@ -97,6 +98,12 @@ struct tee_storage_enum {
 	const struct tee_file_operations *fops;
 };
 
+/*
+ * Protect TA storage directory: avoid race conditions between (create
+ * directory + create file) and (remove directory)
+ */
+static struct mutex ta_dir_mutex = MUTEX_INITIALIZER;
+
 static TEE_Result tee_svc_storage_get_enum(struct user_ta_ctx *utc,
 					   uint32_t enum_id,
 					   struct tee_storage_enum **e_out)
@@ -210,7 +217,9 @@ static TEE_Result tee_svc_storage_remove_corrupt_obj(
 	free(file);
 	dir = tee_svc_storage_create_dirname(sess);
 	if (dir != NULL) {
+		mutex_lock(&ta_dir_mutex);
 		fops->rmdir(dir);
+		mutex_unlock(&ta_dir_mutex);
 		free(dir);
 	}
 
@@ -274,6 +283,8 @@ static TEE_Result tee_svc_storage_create_file(struct tee_ta_session *sess,
 		goto exit;
 	}
 
+	mutex_lock(&ta_dir_mutex);
+
 	/* try and make directory */
 	err = fops->access(dir, TEE_FS_F_OK);
 	if (err) {
@@ -284,7 +295,7 @@ static TEE_Result tee_svc_storage_create_file(struct tee_ta_session *sess,
 		if (tmp < 0) {
 			/* error codes needs better granularity */
 			res = TEE_ERROR_GENERIC;
-			goto exit;
+			goto unlock;
 		}
 	}
 
@@ -293,6 +304,8 @@ static TEE_Result tee_svc_storage_create_file(struct tee_ta_session *sess,
 	if (*fd < 0)
 		res = errno;
 
+unlock:
+	mutex_unlock(&ta_dir_mutex);
 exit:
 	free(dir);
 
@@ -862,8 +875,10 @@ TEE_Result syscall_storage_obj_del(unsigned long obj)
 	dir = tee_svc_storage_create_dirname(sess);
 	if (dir == NULL)
 		return TEE_ERROR_OUT_OF_MEMORY;
+	mutex_lock(&ta_dir_mutex);
 	/* ignore result */
 	fops->rmdir(dir);
+	mutex_unlock(&ta_dir_mutex);
 	free(dir);
 
 	return TEE_SUCCESS;