Vasant Hegde <hegdevas...@linux.vnet.ibm.com> writes:
> diff --git a/arch/powerpc/platforms/powernv/opal-dump.c
> b/arch/powerpc/platforms/powernv/opal-dump.c
> index 543c816fa99e..7e6eeedec32b 100644
> --- a/arch/powerpc/platforms/powernv/opal-dump.c
> +++ b/arch/powerpc/platforms/powernv/opal-dump.c
> @@ -346,21 +345,39 @@ static struct dump_obj *create_dump_obj(uint32_t id,
> size_t size,
> rc = kobject_add(&dump->kobj, NULL, "0x%x-0x%x", type, id);
> if (rc) {
> kobject_put(&dump->kobj);
> - return NULL;
> + return;
> }
>
> + /*
> + * As soon as the sysfs file for this dump is created/activated there is
> + * a chance the opal_errd daemon (or any userspace) might read and
> + * acknowledge the dump before kobject_uevent() is called. If that
> + * happens then there is a potential race between
> + * dump_ack_store->kobject_put() and kobject_uevent() which leads to a
> + * use-after-free of a kernfs object resulting in a kernel crash.
> + *
> + * To avoid that, we need to take a reference on behalf of the bin file,
> + * so that our reference remains valid while we call kobject_uevent().
> + * We then drop our reference before exiting the function, leaving the
> + * bin file to drop the last reference (if it hasn't already).
> + */
> +
> + /* Take a reference for the bin file */
> + kobject_get(&dump->kobj);
> rc = sysfs_create_bin_file(&dump->kobj, &dump->dump_attr);
> if (rc) {
> kobject_put(&dump->kobj);
> - return NULL;
> + /* Drop reference count taken for bin file */
> + kobject_put(&dump->kobj);
> + return;
> }
>
> pr_info("%s: New platform dump. ID = 0x%x Size %u\n",
> __func__, dump->id, dump->size);
>
> kobject_uevent(&dump->kobj, KOBJ_ADD);
> -
> - return dump;
> + /* Drop reference count taken for bin file */
> + kobject_put(&dump->kobj);
> }
I think this would be better if it was reworked along the lines of:
aea948bb80b4 ("powerpc/powernv/elog: Fix race while processing OPAL error log
event.")
cheers
