linux-kernel - Re: [PATCH 2/7] Overlayfs: Use copy-up security hooks

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Date:	Fri, 07 Nov 2014 16:39:21 -0500
From:	Paul Moore <paul@...l-moore.com>
To:	David Howells <dhowells@...hat.com>
Cc:	linux-unionfs@...r.kernel.org, selinux@...ho.nsa.gov,
	linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/7] Overlayfs: Use copy-up security hooks

On Wednesday, November 05, 2014 03:42:38 PM David Howells wrote:
> Use the copy-up security hooks previously provided to allow an LSM to adjust
> the security on a newly created copy and to filter the xattrs copied to
> that file copy.
> 
> Signed-off-by: David Howells <dhowells@...hat.com>
> ---
> 
>  fs/overlayfs/copy_up.c |   12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
> index ea10a8719107..53a357d0a214 100644
> --- a/fs/overlayfs/copy_up.c
> +++ b/fs/overlayfs/copy_up.c
> @@ -58,6 +58,14 @@ int ovl_copy_xattr(struct dentry *old, struct dentry
> *new) error = size;
>  			goto out_free_value;
>  		}
> +		error = security_inode_copy_up_xattr(old, new,
> +						     name, value, &size);

So the LSM must modify the xattr in place?  I suppose that since the @value is 
allocated to the max size it shouldn't be a problem.  Just checking ...

> +		if (error < 0)
> +			goto out_free_value;
> +		if (error == 1) {
> +			error = 0;
> +			continue; /* Discard */
> +		}
>  		error = vfs_setxattr(new, name, value, size, 0);
>  		if (error)
>  			goto out_free_value;

-- 
paul moore
www.paul-moore.com

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