livepatch: robustify klp_register_patch() API error checking

Commit 425595a7fc20 ("livepatch: reuse module loader code to write
relocations") adds a possibility of dereferncing pointers supplied by the
consumer of the livepatch API before sanity (NULL) checking them (patch
and patch->mod).

Spotted by smatch tool.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Jessica Yu <jeyu@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index eb5db6e..28c37fa 100644 (file)
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -876,6 +876,9 @@ int klp_register_patch(struct klp_patch *patch)
 {
        int ret;
 
+       if (!patch || !patch->mod)
+               return -EINVAL;
+
        if (!is_livepatch_module(patch->mod)) {
                pr_err("module %s is not marked as a livepatch module",
                       patch->mod->name);
@@ -885,9 +888,6 @@ int klp_register_patch(struct klp_patch *patch)
        if (!klp_initialized())
                return -ENODEV;
 
-       if (!patch || !patch->mod)
-               return -EINVAL;
-
        /*
         * A reference is taken on the patch module to prevent it from being
         * unloaded.  Right now, we don't allow patch modules to unload since