Re: [PATCH] livepatch: Fix leak on klp_init_patch_early failure path

On Dec 13, 2021, at 2:58 PM, David Vernet [off-list ref] wrote:

Josh Poimboeuf [off-list ref] wrote on Mon [2021-Dec-13 12:10:22 -0800]:

quoted

The patch description needs a few tweaks.  In the kernel we don't use
Markdown for patch descriptions.

A function can be postfixed with a trailing pair of parentheses, like
klp_enable_patch().

Other symbols can be enclosed with single quotes, like 'struct
klp_object'.

I'd also recommend avoiding the excessive use of "we", in favor of more
imperative-type language.

See Documentation/process/submitting-patches.rst for more details.  It's
also a good idea to look at some kernel commit logs to get a general
idea of the kernel patch description style.

Understood, I'll take a read through and re-submit the patch to honor the
norms for Linux kernel patches. My sincere apologies for the noise, and
thank you for the positive and constructive suggestions.

quoted

I don't think the fix will be quite that simple.  For example, if
klp_init_patch_early() fails, that means try_module_get() hasn't been
done, so klp_free_patch_finish() will wrongly do a module_put().

Ugh, good point and thank you for catching that. Another problem with the
current patch is that we'll call kobject_put() on the patch even if we
never call kobject_init on the patch due to patch->objs being NULL.

Perhaps we should pull try_module_get() and the NULL check for patch->objs
out of klp_init_patch_early()? It feels a bit more intuitive to me if
klp_init_patch_early() were only be responsible for initializing kobjects
for the patch and its objects / funcs anyways.

Pulling those logic out of klp_init_patch_early() makes sense to me. 
Alternatively, we may also have a cleanup section in klp_init_patch_early(), 
like below. I am not sure which way will be cleaner. 

Thanks,
Song

diff --git i/kernel/livepatch/core.c w/kernel/livepatch/core.c
index 335d988bd811..20b959c82204 100644
--- i/kernel/livepatch/core.c
+++ w/kernel/livepatch/core.c

@@ -864,7 +864,7 @@ static void klp_init_object_early(struct klp_patch *patch,

 static int klp_init_patch_early(struct klp_patch *patch)
 {
-       struct klp_object *obj;
+       struct klp_object *obj, *obj2;
        struct klp_func *func;

        if (!patch->objs)

@@ -880,7 +880,7 @@ static int klp_init_patch_early(struct klp_patch *patch)

        klp_for_each_object_static(patch, obj) {
                if (!obj->funcs)
-                       return -EINVAL;
+                       goto cleanup;

                klp_init_object_early(patch, obj);

@@ -890,9 +890,15 @@ static int klp_init_patch_early(struct klp_patch *patch)
        }

        if (!try_module_get(patch->mod))
-               return -ENODEV;
+               goto cleanup;

        return 0;
+cleanup:
+       klp_for_each_func_static(patch, obj2) {
+               if (obj2 == obj)
+                       break;  // done
+               /* do clean up */
+       }
 }

 static int klp_init_patch(struct klp_patch *patch)