linux-hardening - Re: [PATCH v2 13/18] sysctl: move sysctl type to ctl_table

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Date: Thu, 7 Dec 2023 12:31:09 +0100
From: Joel Granados <j.granados@...sung.com>
To: Thomas Weißschuh <linux@...ssschuh.net>
CC: Kees Cook <keescook@...omium.org>, "Gustavo A. R. Silva"
	<gustavoars@...nel.org>, Luis Chamberlain <mcgrof@...nel.org>, Iurii Zaikin
	<yzaikin@...gle.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-hardening@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH v2 13/18] sysctl: move sysctl type to ctl_table_header

This is the patch that I said could be on its own to facilitate review

On Mon, Dec 04, 2023 at 08:52:26AM +0100, Thomas Weißschuh wrote:
> In a future commit the sysctl core will only use
> "const struct ctl_table". As a preparation for that move this mutable
> field from "struct ctl_table" to "struct ctl_table_header".
> 
> This is also more correct in general as this is in fact a property of
> the header and not the table itself.
> 
> Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
> ---
>  fs/proc/proc_sysctl.c  | 11 ++++++-----
>  include/linux/sysctl.h | 22 +++++++++++-----------
>  2 files changed, 17 insertions(+), 16 deletions(-)
> 
> diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
> index 689a30196d0c..a398cc77637f 100644
> --- a/fs/proc/proc_sysctl.c
> +++ b/fs/proc/proc_sysctl.c
> @@ -31,7 +31,7 @@ static const struct inode_operations proc_sys_dir_operations;
>  
>  /* Support for permanently empty directories */
>  static struct ctl_table sysctl_mount_point[] = {
> -	{.type = SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY }
> +	{ }
>  };
>  
>  /**
> @@ -49,11 +49,11 @@ struct ctl_table_header *register_sysctl_mount_point(const char *path)
>  EXPORT_SYMBOL(register_sysctl_mount_point);
>  
>  #define sysctl_is_perm_empty_ctl_header(hptr)		\
> -	(hptr->ctl_table[0].type == SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY)
> +	(hptr->type == SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY)
>  #define sysctl_set_perm_empty_ctl_header(hptr)		\
> -	(hptr->ctl_table[0].type = SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY)
> +	(hptr->type = SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY)
>  #define sysctl_clear_perm_empty_ctl_header(hptr)	\
> -	(hptr->ctl_table[0].type = SYSCTL_TABLE_TYPE_DEFAULT)
> +	(hptr->type = SYSCTL_TABLE_TYPE_DEFAULT)
>  
>  void proc_sys_poll_notify(struct ctl_table_poll *poll)
>  {
> @@ -231,7 +231,8 @@ static int insert_header(struct ctl_dir *dir, struct ctl_table_header *header)
>  		return -EROFS;
>  
>  	/* Am I creating a permanently empty directory? */
> -	if (sysctl_is_perm_empty_ctl_header(header)) {
> +	if (header->ctl_table == sysctl_mount_point ||
> +	    sysctl_is_perm_empty_ctl_header(header)) {
Why do you have to check that it is equal to sysctl_mount_point? It
should be enough to make sure that the type of PERMANENTLY_EMPTY. no?

>  		if (!RB_EMPTY_ROOT(&dir->root))
>  			return -EINVAL;
>  		sysctl_set_perm_empty_ctl_header(dir_h);
> diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
> index ada36ef8cecb..061ea65104be 100644
> --- a/include/linux/sysctl.h
> +++ b/include/linux/sysctl.h
> @@ -137,17 +137,6 @@ struct ctl_table {
>  	void *data;
>  	int maxlen;
>  	umode_t mode;
> -	/**
> -	 * enum type - Enumeration to differentiate between ctl target types
> -	 * @SYSCTL_TABLE_TYPE_DEFAULT: ctl target with no special considerations
> -	 * @SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY: Used to identify a permanently
> -	 *                                       empty directory target to serve
> -	 *                                       as mount point.
> -	 */
> -	enum {
> -		SYSCTL_TABLE_TYPE_DEFAULT,
> -		SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY
> -	} type;
>  	proc_handler *proc_handler;	/* Callback for text formatting */
>  	struct ctl_table_poll *poll;
>  	void *extra1;
> @@ -188,6 +177,17 @@ struct ctl_table_header {
>  	struct ctl_dir *parent;
>  	struct ctl_node *node;
>  	struct hlist_head inodes; /* head for proc_inode->sysctl_inodes */
> +	/**
> +	 * enum type - Enumeration to differentiate between ctl target types
> +	 * @SYSCTL_TABLE_TYPE_DEFAULT: ctl target with no special considerations
> +	 * @SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY: Used to identify a permanently
> +	 *                                       empty directory target to serve
> +	 *                                       as mount point.
> +	 */
> +	enum {
> +		SYSCTL_TABLE_TYPE_DEFAULT,
> +		SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY
> +	} type;
>  };
>  
>  struct ctl_dir {
> 
> -- 
> 2.43.0
> 

-- 

Joel Granados

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