linux-kernel - Re: [PATCH] nfsd: nfsd should drop CAP

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Message-ID: <20090318173221.GA16077@fieldses.org>
Date:	Wed, 18 Mar 2009 13:32:21 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	"Serge E. Hallyn" <serue@...ibm.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	Igor Zhbanov <izh1979@...il.com>, stable@...nel.org
Subject: Re: [PATCH] nfsd: nfsd should drop CAP_MKNOD for non-root

On Wed, Mar 18, 2009 at 12:08:43PM -0500, Serge E. Hallyn wrote:
> Quoting J. Bruce Fields (bfields@...ldses.org):
> > From: J. Bruce Fields <bfields@...i.umich.edu>
> > 
> > Since creating a device node is normally an operation requiring special
> > privilege, Igor Zhbanov points out that it is surprising (to say the
> > least) that a client can, for example, create a device node on a
> > filesystem exported with root_squash.
> > 
> > So, make sure CAP_MKNOD is among the capabilities dropped when an nfsd
> > thread handles a request from a non-root user.
> > 
> > Reported-by: Igor Zhbanov <izh1979@...il.com>
> > Cc: stable@...nel.org
> > Signed-off-by: J. Bruce Fields <bfields@...i.umich.edu>
> 
> Acked-by: Serge Hallyn <serue@...ibm.com>
> 
> I assume CAP_LINUX_IMMUTABLE simply does not apply to nfs?

Right.  We shouldn't care how it's set.

> And, you're adding CAP_FS_MASK_B1 in anticipation of labeled nfs?

That's unchanged (would have been clearer if I hadn't re-line-wrapped in
the same patch).

> Though, I was going to send a patch later today or tomorrow (figure I
> should do some ltp testing) adding CAP_MKNOD to the whole
> CAP_FS_MASK_B0 (and CAP_LINUX_IMMUTABLE and CAP_FS_MASK_B1 to
> CAP_FS_SET).  That will conflict with this one.

OK, feel free to revert this at that point if necessary.

--b.

> 
> thanks,
> -serge
> 
> > ---
> >  include/linux/capability.h |    6 ++++--
> >  1 files changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/linux/capability.h b/include/linux/capability.h
> > index 1b98725..4864a43 100644
> > --- a/include/linux/capability.h
> > +++ b/include/linux/capability.h
> > @@ -393,8 +393,10 @@ struct cpu_vfs_cap_data {
> >  # define CAP_FULL_SET     ((kernel_cap_t){{ ~0, ~0 }})
> >  # define CAP_INIT_EFF_SET ((kernel_cap_t){{ ~CAP_TO_MASK(CAP_SETPCAP), ~0 }})
> >  # define CAP_FS_SET       ((kernel_cap_t){{ CAP_FS_MASK_B0, CAP_FS_MASK_B1 } })
> > -# define CAP_NFSD_SET     ((kernel_cap_t){{ CAP_FS_MASK_B0|CAP_TO_MASK(CAP_SYS_RESOURCE), \
> > -					CAP_FS_MASK_B1 } })
> > +# define CAP_NFSD_SET     ((kernel_cap_t){{ CAP_FS_MASK_B0 \
> > +					    | CAP_TO_MASK(CAP_SYS_RESOURCE) \
> > +					    | CAP_TO_MASK(CAP_MKNOD), \
> > +					    CAP_FS_MASK_B1 } })
> > 
> >  #endif /* _KERNEL_CAPABILITY_U32S != 2 */
> > 
> > -- 
> > 1.6.0.4
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