Re: [PATCH v2] fs/proc/proc_sysctl.c: always initialize i_uid/i_gid

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: "Thomas Weißschuh" <linux@weissschuh.net>
Date: Fri, 22 Mar 2024 20:51:11 +0100
> Commit e79c6a4fc923 ("net: make net namespace sysctls belong to container's owner")
> added default values for i_uid/i_gid.

The commit that added the default is 5ec27ec735ba ("fs/proc/proc_sysctl.c:
fix the default values of i_uid/i_gid on /proc/sys inodes.")


> These however are only used when ctl_table_root->set_ownership is not
> implemented.
> But the callbacks themselves could fail to compute i_uid/i_gid and they
> all need to have the same fallback logic for this case.
> 
> This is unnecessary code duplication and prone to errors.
> For example net_ctl_set_ownership() missed the fallback.
> 
> Instead always initialize i_uid/i_gid inside the sysfs core so
> set_ownership() can safely skip setting them.
> 
> Fixes: e79c6a4fc923 ("net: make net namespace sysctls belong to container's owner")
> Cc: stable@vger.kernel.org
> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> ---
> Changes in v2:
> - Move the fallback logic to the sysctl core
> - Link to v1: https://lore.kernel.org/r/20240315-sysctl-net-ownership-v1-1-2b465555a292@weissschuh.net
> ---
>  fs/proc/proc_sysctl.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
> index 37cde0efee57..9e34ab9c21e4 100644
> --- a/fs/proc/proc_sysctl.c
> +++ b/fs/proc/proc_sysctl.c
> @@ -479,12 +479,10 @@ static struct inode *proc_sys_make_inode(struct super_block *sb,
>  			make_empty_dir_inode(inode);
>  	}
>  
> +	inode->i_uid = GLOBAL_ROOT_UID;
> +	inode->i_gid = GLOBAL_ROOT_GID;
>  	if (root->set_ownership)
>  		root->set_ownership(head, table, &inode->i_uid, &inode->i_gid);
> -	else {
> -		inode->i_uid = GLOBAL_ROOT_UID;
> -		inode->i_gid = GLOBAL_ROOT_GID;
> -	}
>  
>  	return inode;
>  }
> 
> ---
> base-commit: ff9c18e435b042596c9d48badac7488e3fa76a55
> change-id: 20240315-sysctl-net-ownership-bc4e17eaeea6
> 
> Best regards,
> -- 
> Thomas Weißschuh <linux@weissschuh.net>