linux-kernel - Re: [PATCH 3/4] module: sysfs: Add notes attributes through attribute

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Message-ID: <4ed64526-9ef0-49ed-ae97-a0df89136f89@suse.com>
Date: Wed, 18 Dec 2024 14:13:07 +0100
From: Petr Pavlu <petr.pavlu@...e.com>
To: Thomas Weißschuh <linux@...ssschuh.net>
Cc: Luis Chamberlain <mcgrof@...nel.org>,
 Sami Tolvanen <samitolvanen@...gle.com>, Daniel Gomez
 <da.gomez@...sung.com>, Kees Cook <kees@...nel.org>,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>,
 linux-modules@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-hardening@...r.kernel.org
Subject: Re: [PATCH 3/4] module: sysfs: Add notes attributes through
 attribute_group

On 12/16/24 20:16, Thomas Weißschuh wrote:
> A kobject is meant to manage the lifecycle of some resource.
> However the module sysfs code only creates a kobject to get a
> "notes" subdirectory in sysfs.
> This can be achieved easier and cheaper by using a sysfs group.
> Switch the notes attribute code to such a group, similar to how the
> section allocation in the same file already works.
> 
> Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
> ---
>  kernel/module/sysfs.c | 48 +++++++++++++++++++++++-------------------------
>  1 file changed, 23 insertions(+), 25 deletions(-)
> 
> diff --git a/kernel/module/sysfs.c b/kernel/module/sysfs.c
> index 935629ac21fa16504ddb5f3762af5539572c3bf1..4f37970f99c999589257713926395686f03103e6 100644
> --- a/kernel/module/sysfs.c
> +++ b/kernel/module/sysfs.c
> @@ -145,20 +145,17 @@ static void remove_sect_attrs(struct module *mod)
>   */
>  
>  struct module_notes_attrs {
> -	struct kobject *dir;
> -	unsigned int notes;
> -	struct bin_attribute attrs[] __counted_by(notes);
> +	struct attribute_group grp;
> +	struct bin_attribute attrs[];
>  };
>  
> -static void free_notes_attrs(struct module_notes_attrs *notes_attrs,
> -			     unsigned int i)
> +static void free_notes_attrs(struct module_notes_attrs *notes_attrs)
>  {
> -	if (notes_attrs->dir) {
> -		while (i-- > 0)
> -			sysfs_remove_bin_file(notes_attrs->dir,
> -					      &notes_attrs->attrs[i]);
> -		kobject_put(notes_attrs->dir);
> -	}
> +	struct bin_attribute **bin_attr;
> +
> +	for (bin_attr = notes_attrs->grp.bin_attrs; *bin_attr; bin_attr++)

Similarly as commented on patch #2, this results in a NULL dereference
when add_notes_attrs() fails to allocate gattr.

> +		kfree((*bin_attr)->attr.name);

This line causes that the name string is freed twice on a module
unload, here and in free_sect_attrs(). Notice that function
add_notes_attrs() takes each name directly from mod->sect_attrs, without
calling kstrdup():

nattr->attr.name = mod->sect_attrs->attrs[loaded].battr.attr.name;

> +	kfree(notes_attrs->grp.bin_attrs);
>  	kfree(notes_attrs);
>  }
>  
> @@ -166,6 +163,7 @@ static int add_notes_attrs(struct module *mod, const struct load_info *info)
>  {
>  	unsigned int notes, loaded, i;
>  	struct module_notes_attrs *notes_attrs;
> +	struct bin_attribute **gattr;
>  	struct bin_attribute *nattr;
>  	int ret;
>  
> @@ -184,7 +182,15 @@ static int add_notes_attrs(struct module *mod, const struct load_info *info)
>  	if (!notes_attrs)
>  		return -ENOMEM;
>  
> -	notes_attrs->notes = notes;
> +	gattr = kcalloc(notes + 1, sizeof(*gattr), GFP_KERNEL);
> +	if (!gattr) {
> +		ret = -ENOMEM;
> +		goto out;
> +	}
> +
> +	notes_attrs->grp.name = "notes";
> +	notes_attrs->grp.bin_attrs = gattr;
> +
>  	nattr = &notes_attrs->attrs[0];
>  	for (loaded = i = 0; i < info->hdr->e_shnum; ++i) {
>  		if (sect_empty(&info->sechdrs[i]))
> @@ -196,35 +202,27 @@ static int add_notes_attrs(struct module *mod, const struct load_info *info)
>  			nattr->size = info->sechdrs[i].sh_size;
>  			nattr->private = (void *)info->sechdrs[i].sh_addr;
>  			nattr->read = sysfs_bin_attr_simple_read;
> -			++nattr;
> +			*(gattr++) = nattr++;
>  		}
>  		++loaded;
>  	}
>  
> -	notes_attrs->dir = kobject_create_and_add("notes", &mod->mkobj.kobj);
> -	if (!notes_attrs->dir) {
> -		ret = -ENOMEM;
> +	ret = sysfs_create_group(&mod->mkobj.kobj, &notes_attrs->grp);
> +	if (ret)
>  		goto out;
> -	}
> -
> -	for (i = 0; i < notes; ++i) {
> -		ret = sysfs_create_bin_file(notes_attrs->dir, &notes_attrs->attrs[i]);
> -		if (ret)
> -			goto out;
> -	}
>  
>  	mod->notes_attrs = notes_attrs;
>  	return 0;
>  
>  out:
> -	free_notes_attrs(notes_attrs, i);
> +	free_notes_attrs(notes_attrs);
>  	return ret;
>  }
>  
>  static void remove_notes_attrs(struct module *mod)
>  {
>  	if (mod->notes_attrs)
> -		free_notes_attrs(mod->notes_attrs, mod->notes_attrs->notes);
> +		free_notes_attrs(mod->notes_attrs);
>  }

If the patch tries to unify handling of sect_attrs and notes_attrs,
should remove_notes_attrs() call also sysfs_remove_group() and reset
mod->notes_attrs to match what is done in remove_sect_attrs()?

>  
>  #else /* !CONFIG_KALLSYMS */
> 

-- 
Thanks,
Petr