On Mon, 3 Jun 2019, YueHaibing wrote:
> In module_add_modinfo_attrs if sysfs_create_file
> fails, we forget to free allocated modinfo_attrs
> and roll back the sysfs files.
>
> Fixes: 03e88ae1b13d ("[PATCH] fix module sysfs files reference counting")
> Signed-off-by: YueHaibing <yuehaib...@huawei.com>
> ---
> v3: reuse module_remove_modinfo_attrs
> v2: free from '--i' instead of 'i--'
> ---
> kernel/module.c | 21 ++++++++++++++++-----
> 1 file changed, 16 insertions(+), 5 deletions(-)
I'm afraid it is not completely correct.
> diff --git a/kernel/module.c b/kernel/module.c
> index 80c7c09..c6b8912 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -1697,6 +1697,8 @@ static int add_usage_links(struct module *mod)
> return ret;
> }
>
> +static void module_remove_modinfo_attrs(struct module *mod, int end);
> +
> static int module_add_modinfo_attrs(struct module *mod)
> {
> struct module_attribute *attr;
> @@ -1711,24 +1713,33 @@ static int module_add_modinfo_attrs(struct module
> *mod)
> return -ENOMEM;
>
> temp_attr = mod->modinfo_attrs;
> - for (i = 0; (attr = modinfo_attrs[i]) && !error; i++) {
> + for (i = 0; (attr = modinfo_attrs[i]); i++) {
> if (!attr->test || attr->test(mod)) {
> memcpy(temp_attr, attr, sizeof(*temp_attr));
> sysfs_attr_init(&temp_attr->attr);
> error = sysfs_create_file(&mod->mkobj.kobj,
> &temp_attr->attr);
> + if (error)
> + goto error_out;
sysfs_create_file() failed, so we need to clear all previously processed
attrs and not the current one.
> ++temp_attr;
> }
> }
> +
> + return 0;
> +
> +error_out:
> + module_remove_modinfo_attrs(mod, --i);
It says "call sysfs_remove_file() on all attrs ending with --i included
(all correctly processed attrs).
> return error;
> }
>
> -static void module_remove_modinfo_attrs(struct module *mod)
> +static void module_remove_modinfo_attrs(struct module *mod, int end)
> {
> struct module_attribute *attr;
> int i;
>
> for (i = 0; (attr = &mod->modinfo_attrs[i]); i++) {
> + if (end >= 0 && i > end)
> + break;
If end == 0, you break the loop without calling sysfs_remove_file(), which
is a bug if you called module_remove_modinfo_attrs(mod, 0).
Calling module_remove_modinfo_attrs(mod, i); in module_add_modinfo_attrs()
under error_out label and changing the condition here to
if (end >= 0 && i >= end)
break;
should work as expected.
But let me ask another question and it might be more to Jessica. Why is
there even a call to attr->free(mod); (if it exists) in
module_remove_modinfo_attrs()? The same is in free_modinfo() (as opposed
to setup_modinfo() where attr->setup(mod) is called. Is it because
free_modinfo() is called only in load_module()'s error path, while
module_remove_modinfo_attrs() is called even in free_module() path?
kfree() checks for NULL pointer, so there is no bug, but it is certainly
not nice and it calls for cleanup. But I may be missing something.
Regards,
Miroslav
