livepatch: enforce patch stacking semantics

Only allow the topmost patch on the stack to be enabled or disabled, so
that patches can't be removed or added in an arbitrary order.

Suggested-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

1 files changed, 10 insertions, 0 deletions

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 3d9c00b5223a..2401e7f955d3 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -379,6 +379,11 @@ static int __klp_disable_patch(struct klp_patch *patch)
         struct klp_object *obj;
         int ret;
 
+        /* enforce stacking: only the last enabled patch can be disabled */
+        if (!list_is_last(&patch->list, &klp_patches) &&
+            list_next_entry(patch, list)->state == KLP_ENABLED)
+                return -EBUSY;
+
         pr_notice("disabling patch '%s'\n", patch->mod->name);
 
         for (obj = patch->objs; obj->funcs; obj++) {
@@ -435,6 +440,11 @@ static int __klp_enable_patch(struct klp_patch *patch)
         if (WARN_ON(patch->state != KLP_DISABLED))
                 return -EINVAL;
 
+        /* enforce stacking: only the first disabled patch can be enabled */
+        if (patch->list.prev != &klp_patches &&
+            list_prev_entry(patch, list)->state == KLP_DISABLED)
+                return -EBUSY;
+
         pr_notice_once("tainting kernel with TAINT_LIVEPATCH\n");
         add_taint(TAINT_LIVEPATCH, LOCKDEP_STILL_OK);