linux-kernel - Re: [PATCH 4/9] selinux: Implementation for inode_copy_up

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Message-ID: <f8bcf395-e07d-2d8d-ee47-a7628b4835c1@tycho.nsa.gov>
Date:	Wed, 13 Jul 2016 10:54:39 -0400
From:	Stephen Smalley <sds@...ho.nsa.gov>
To:	Vivek Goyal <vgoyal@...hat.com>, miklos@...redi.hu,
	pmoore@...hat.com, casey@...aufler-ca.com,
	linux-kernel@...r.kernel.org, linux-unionfs@...r.kernel.org,
	linux-security-module@...r.kernel.org
Cc:	dwalsh@...hat.com, dhowells@...hat.com, viro@...IV.linux.org.uk,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 4/9] selinux: Implementation for inode_copy_up_xattr()
 hook

On 07/13/2016 10:44 AM, Vivek Goyal wrote:
> When a file is copied up in overlay, we have already created file on upper/
> with right label and there is no need to copy up selinux label/xattr from
> lower file to upper file. In fact in case of context mount, we don't want
> to copy up label as newly created file got its label from context= option.
> 
> Signed-off-by: Vivek Goyal <vgoyal@...hat.com>

Acked-by: Stephen Smalley <sds@...ho.nsa.gov>

> ---
>  security/selinux/hooks.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index c82ee54..4fda548 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -3290,6 +3290,21 @@ static int selinux_inode_copy_up(struct dentry *src, struct cred **new)
>  	return 0;
>  }
>  
> +static int selinux_inode_copy_up_xattr(const char *name)
> +{
> +	/* The copy_up hook above sets the initial context on an inode, but we
> +	 * don't then want to overwrite it by blindly copying all the lower
> +	 * xattrs up.  Instead, we have to filter out SELinux-related xattrs.
> +	 */
> +	if (strcmp(name, XATTR_NAME_SELINUX) == 0)
> +		return 1; /* Discard */
> +	/*
> +	 * Any other attribute apart from SELINUX is not claimed, supported
> +	 * by selinux.
> +	 */
> +	return -EOPNOTSUPP;
> +}
> +
>  /* file security operations */
>  
>  static int selinux_revalidate_file_permission(struct file *file, int mask)
> @@ -6077,6 +6092,7 @@ static struct security_hook_list selinux_hooks[] = {
>  	LSM_HOOK_INIT(inode_listsecurity, selinux_inode_listsecurity),
>  	LSM_HOOK_INIT(inode_getsecid, selinux_inode_getsecid),
>  	LSM_HOOK_INIT(inode_copy_up, selinux_inode_copy_up),
> +	LSM_HOOK_INIT(inode_copy_up_xattr, selinux_inode_copy_up_xattr),
>  
>  	LSM_HOOK_INIT(file_permission, selinux_file_permission),
>  	LSM_HOOK_INIT(file_alloc_security, selinux_file_alloc_security),
>