[PATCH v2] livepatch: Fix NULL pointer dereference in klp_find_func()

A NULL old_name in a newly loaded livepatch's function entry causes a
NULL pointer dereference in strcmp():

  klp_init_patch()
    klp_add_nops()
      klp_find_func()
        strcmp(old_func->old_name, func->old_name)

Add klp_check_patch() at the beginning of klp_enable_patch() to reject
patches with NULL old_name before they reach this code path.

Reported-by: sashiko-bot <[email protected]>
Closes: https://lore.kernel.org/live-patching/[email protected]/
Suggested-by: Petr Mladek <[email protected]>
Suggested-by: Miroslav Benes <[email protected]>
Signed-off-by: Yafang Shao <[email protected]>
Acked-by: Miroslav Benes <[email protected]>
---
 kernel/livepatch/core.c | 34 ++++++++++++++++++++++------------
 1 file changed, 22 insertions(+), 12 deletions(-)

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 28d15ba58a26..a240d1144e89 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -799,9 +799,6 @@ void klp_free_replaced_patches_async(struct klp_patch *new_patch)
 
 static int klp_init_func(struct klp_object *obj, struct klp_func *func)
 {
-	if (!func->old_name)
-		return -EINVAL;
-
 	/*
 	 * NOPs get the address later. The patched module must be loaded,
 	 * see klp_init_object_loaded().
@@ -1092,6 +1089,25 @@ static int __klp_enable_patch(struct klp_patch *patch)
 	return ret;
 }
 
+static int klp_check_patch(struct klp_patch *patch)
+{
+	struct klp_object *obj;
+	struct klp_func *func;
+
+	if (!patch || !patch->mod || !patch->objs)
+		return -EINVAL;
+
+	klp_for_each_object_static(patch, obj) {
+		if (!obj->funcs)
+			return -EINVAL;
+		klp_for_each_func_static(obj, func) {
+			if (!func->old_name)
+				return -EINVAL;
+		}
+	}
+	return 0;
+}
+
 /**
  * klp_enable_patch() - enable the livepatch
  * @patch:	patch to be enabled
@@ -1108,16 +1124,10 @@ static int __klp_enable_patch(struct klp_patch *patch)
 int klp_enable_patch(struct klp_patch *patch)
 {
 	int ret;
-	struct klp_object *obj;
-
-	if (!patch || !patch->mod || !patch->objs)
-		return -EINVAL;
-
-	klp_for_each_object_static(patch, obj) {
-		if (!obj->funcs)
-			return -EINVAL;
-	}
 
+	ret = klp_check_patch(patch);
+	if (ret)
+		return ret;
 
 	if (!is_livepatch_module(patch->mod)) {
 		pr_err("module %s is not marked as a livepatch module\n",
-- 
2.52.0