[RFC] livepatch: unpatch all klp_objects if klp_module_coming fails

[Joe Lawrence]

When an incoming module is considered for livepatching by
klp_module_coming(), it iterates over multiple patches and multiple
kernel objects in this order:

	list_for_each_entry(patch, &klp_patches, list) {
		klp_for_each_object(patch, obj) {

which means that if one of the kernel objects fail to patch for whatever
reason, klp_module_coming()'s error path should double back and unpatch
any previous kernel object that was patched for a previous patch.

Reported-by: Miroslav Benes <mbenes@xxxxxxx>
Signed-off-by: Joe Lawrence <joe.lawrence@xxxxxxxxxx>
---
 kernel/livepatch/core.c | 30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index aca62c4b8616..7f5192618cc8 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -889,6 +889,8 @@ int klp_module_coming(struct module *mod)
 				goto err;
 			}
 
+pr_err("JL: klp_patch_object(%p) patch=%p obj->name: %s\n", obj, patch, obj->name);
+
 			ret = klp_patch_object(obj);
 			if (ret) {
 				pr_warn("failed to apply patch '%s' to module '%s' (%d)\n",
@@ -919,7 +921,33 @@ int klp_module_coming(struct module *mod)
 	pr_warn("patch '%s' failed for module '%s', refusing to load module '%s'\n",
 		patch->mod->name, obj->mod->name, obj->mod->name);
 	mod->klp_alive = false;
-	klp_free_object_loaded(obj);
+
+	/*
+	 * Run back through the patch list and unpatch any klp_object that
+	 * was patched before hitting an error above.
+	 */
+
+	list_for_each_entry(patch, &klp_patches, list) {
+
+		if (!patch->enabled || patch == klp_transition_patch)
+			continue;
+
+		klp_for_each_object(patch, obj) {
+
+			if (!obj->patched || !klp_is_module(obj) ||
+			    strcmp(obj->name, mod->name))
+				continue;
+
+			klp_pre_unpatch_callback(obj);
+pr_err("JL: klp_unpatch_object(%p) patch=%p obj->name: %s\n", obj, patch, obj->name);
+			klp_unpatch_object(obj);
+			klp_post_unpatch_callback(obj);
+			klp_free_object_loaded(obj);
+
+			break;
+		}
+	}
+
 	mutex_unlock(&klp_mutex);
 
 	return ret;
-- 
2.7.5