linux-kernel - Re: [RFC PATCH] Security: ignore private inode from security_file

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Date:	Thu, 16 Apr 2015 08:35:37 -0700
From:	Casey Schaufler <casey@...aufler-ca.com>
To:	Seung-Woo Kim <sw0312.kim@...sung.com>, james.l.morris@...cle.com,
	serge@...lyn.com, linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org
CC:	sumit.semwal@...aro.org, linaro-mm-sig@...ts.linaro.org,
	jy0922.shim@...sung.com, Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [RFC PATCH] Security: ignore private inode from security_file_receive

On 4/16/2015 6:40 AM, Seung-Woo Kim wrote:
> The dma-buf fd from anon_inode can be shared across processes, but
> there is no way to set security permission for the fd. So this
> patch fix just to ignore private inode from security_file_receive.
>
> Signed-off-by: Seung-Woo Kim <sw0312.kim@...sung.com>
> ---
>
> If security like smack is enabled, the dmabuf fd can not be shared between
> processes via unix domain socket. I am not familiar with security, so I am
> not sure that this kind of patch can be acceptable.

If an IS_PRIVATE() check is appropriate, it should be in
smack_file_receive(), not security_file_receive(). Why are you
looking at file->f_path.dentry->d_inode? That's not used in the
Smack access check. You'd want file->f_inode if anything.

Naked-by: Casey Schaufler <casey@...aufler-ca.com>

>
> Is there other option to share dmabuf fd via socket with security check?
>
> Best Regards,
> - Seung-Woo Kim
>
> ---
>  security/security.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
>
> diff --git a/security/security.c b/security/security.c
> index 730ac65..c57354c 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -810,6 +810,9 @@ int security_file_send_sigiotask(struct task_struct *tsk,
>  
>  int security_file_receive(struct file *file)
>  {
> +
> +	if (unlikely(IS_PRIVATE(file->f_path.dentry->d_inode)))
> +		return 0;
>  	return security_ops->file_receive(file);
>  }
>  

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