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From: Vivek Goyal <vgoyal@redhat.com>
To: Dmitry Kasatkin <dmitry.kasatkin@intel.com>
Cc: linux-security-module@vger.kernel.org,
	linux-kernel@vger.kernel.org, casey@schaufler-ca.com,
	zohar@linux.vnet.ibm.com, viro@zeniv.linux.org.uk,
	linux-fsdevel@vger.kernel.org
Subject: Re: [RFC 1/1] xattr: provide integrity. namespace to read real values
Date: Thu, 14 Feb 2013 15:05:57 -0500	[thread overview]
Message-ID: <20130214200557.GF16671@redhat.com> (raw)
In-Reply-To: <959cfd74266e82f72e5879c6c8b798d76f6cad31.1360746454.git.dmitry.kasatkin@intel.com>

On Wed, Feb 13, 2013 at 11:07:49AM +0200, Dmitry Kasatkin wrote:
> User space tools use getxattr() system call to read values of extended
> attributes. getxattr() system call uses vfs_getattr(), which for "security."
> namespace might get a value of the xattr indirectly from LSM via calling
> xattr_getsecurity(). For that reason value set by setxattr and read by getxattr
> might differ.
> 
> Here is an example of SMACK label, which shows that set and read values are
> different:
> 
>   setfattr -n security.SMACK64 -v "hello world" foo
>   getfattr -n security.SMACK64 foo
>   # file: foo
>   security.SMACK64="hello"
> 
> EVM uses vfs_getxattr_alloc(), which directly reads xattr values from the file
> system. When performing the file system labeling with digital signatures, it is
> necessary to read real xattr values in order to generate the correct signatures.
> 
> This patch adds the virtual "integrity." name space, which allows to bypass
> calling LSM and read real extended attribute values.
> 
>   getfattr -e text -n integrity.SMACK64 foo
>   # file: foo
>   integrity.SMACK64="hello world"

Without knowing anything about xattr or LSM, to me it is odd that I
write an xattr using name "security.SMACK64" and read back the same
attribute using different name "integrity.SMACK64".

Thanks
Vivek

  parent reply	other threads:[~2013-02-14 20:05 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-02-13  9:07 [RFC 1/1] xattr: provide integrity. namespace to read real values Dmitry Kasatkin
2013-02-14  7:48 ` Kasatkin, Dmitry
2013-02-14 20:05 ` Vivek Goyal [this message]
2013-02-25 12:25   ` Kasatkin, Dmitry

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