audit: fix a memleak caused by auditing load module

module.name will be allocated unconditionally when auditing load
module, and audit_log_start() can fail with other reasons, or
audit_log_exit maybe not called, caused module.name is not freed

so free module.name in audit_free_context and __audit_syscall_exit

unreferenced object 0xffff88af90837d20 (size 8):
  comm "modprobe", pid 1036, jiffies 4294704867 (age 3069.138s)
  hex dump (first 8 bytes):
    69 78 67 62 65 00 ff ff                          ixgbe...
  backtrace:
    [<0000000008da28fe>] __audit_log_kern_module+0x33/0x80
    [<00000000c1491e61>] load_module+0x64f/0x3850
    [<000000007fc9ae3f>] __do_sys_init_module+0x218/0x250
    [<0000000000d4a478>] do_syscall_64+0x117/0x400
    [<000000004924ded8>] entry_SYSCALL_64_after_hwframe+0x49/0xbe
    [<000000007dc331dd>] 0xffffffffffffffff

Fixes: ca86cad7 ("audit: log module name on init_module")
Signed-off-by: Zhang Yu <zhangyu31@baidu.com>
Signed-off-by: Li RongQing <lirongqing@baidu.com>
[PM: manual merge fixup in __audit_syscall_exit()]
Signed-off-by: Paul Moore <paul@paul-moore.com>

kernel/auditsc.c

@@ -840,6 +840,13 @@ static inline void audit_proctitle_free(struct audit_context *context)
 	context->proctitle.len = 0;
 }
 
+static inline void audit_free_module(struct audit_context *context)
+{
+	if (context->type == AUDIT_KERN_MODULE) {
+		kfree(context->module.name);
+		context->module.name = NULL;
+	}
+}
 static inline void audit_free_names(struct audit_context *context)
 {
 	struct audit_names *n, *next;
@@ -923,6 +930,7 @@ int audit_alloc(struct task_struct *tsk)
 
 static inline void audit_free_context(struct audit_context *context)
 {
+	audit_free_module(context);
 	audit_free_names(context);
 	unroll_tree_refs(context, NULL, 0);
 	free_tree_refs(context);
@@ -1266,7 +1274,6 @@ static void show_special(struct audit_context *context, int *call_panic)
 		audit_log_format(ab, "name=");
 		if (context->module.name) {
 			audit_log_untrustedstring(ab, context->module.name);
-			kfree(context->module.name);
 		} else
 			audit_log_format(ab, "(null)");
 
@@ -1697,6 +1704,7 @@ void __audit_syscall_exit(int success, long return_code)
 	context->in_syscall = 0;
 	context->prio = context->state == AUDIT_RECORD_CONTEXT ? ~0ULL : 0;
 
+	audit_free_module(context);
 	audit_free_names(context);
 	unroll_tree_refs(context, NULL, 0);
 	audit_free_aux(context);