On Tue, Dec 21, 2021 at 07:39:31AM -0800, David Vernet wrote:
> When enabling a klp patch with klp_enable_patch(), klp_init_patch_early()
> is invoked to initialize the kobjects for the patch itself, as well as the
> 'struct klp_object' and 'struct klp_func' objects that comprise it.
> However, there are some error paths in klp_enable_patch() where some
> kobjects may have been initialized with kobject_init(), but an error code
> is still returned due to e.g. a 'struct klp_object' having a NULL funcs
> pointer.
>
> In these paths, the initial reference of the kobject of the 'struct
> klp_patch' may never be released, along with one or more of its objects and
> their functions, as kobject_put() is not invoked on the cleanup path if
> klp_init_patch_early() returns an error code.
>
> For example, if an object entry such as the following were added to the
> sample livepatch module's klp patch, it would cause the vmlinux klp_object,
> and its klp_func which updates 'cmdline_proc_show', to never be released:
>
> static struct klp_object objs[] = {
> {
> /* name being NULL means vmlinux */
> .funcs = funcs,
> },
> {
> /* NULL funcs -- would cause reference leak */
> .name = "kvm",
> }, { }
> };
>
> Without this change, if CONFIG_DEBUG_KOBJECT is enabled, and the sample klp
> patch is loaded, the kobjects (the patch, the vmlinux 'struct klp_object',
> and its func) are observed as initialized, but never released, in the dmesg
> log output. With the change, these kobject references no longer fail to be
> released as the error case is properly handled before they are initialized.
>
> Signed-off-by: David Vernet <void@xxxxxxxxxxxxx>
> ---
> v3:
> - Update patch description to not specifically claim to be fixing a
> "leak", but rather a kobject reference counting bug.
> - Make klp_init_patch_early() void to match klp_init_object_early() and
> klp_init_func_early(), and move the arg validation that previously
> resided there into klp_enable_patch() (where other argument validation
> logic already resides).
Acked-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
--
Josh
