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>

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 3d9c00b5223af9f224d9ea5659de9e4ff1698f6d..2401e7f955d32dbc62b85b1978cc711c5cb136b1 100644 (file)
--- 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);