linux-kernel - Re: [PATCH] ovl: filter of trusted xattr results in audit

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Message-ID: <20191007164037.GA1012698@kroah.com>
Date:   Mon, 7 Oct 2019 18:40:37 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Mark Salyzyn <salyzyn@...roid.com>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        linux-security-module@...r.kernel.org, stable@...r.kernel.org,
        Miklos Szeredi <miklos@...redi.hu>,
        linux-unionfs@...r.kernel.org
Subject: Re: [PATCH] ovl: filter of trusted xattr results in audit

On Mon, Oct 07, 2019 at 06:17:25PM +0200, Greg Kroah-Hartman wrote:
> On Mon, Oct 07, 2019 at 06:16:16PM +0200, Greg Kroah-Hartman wrote:
> > On Mon, Oct 07, 2019 at 09:09:16AM -0700, Mark Salyzyn wrote:
> > > When filtering xattr list for reading, presence of trusted xattr
> > > results in a security audit log.  However, if there is other content
> > > no errno will be set, and if there isn't, the errno will be -ENODATA
> > > and not -EPERM as is usually associated with a lack of capability.
> > > The check does not block the request to list the xattrs present.
> > > 
> > > Switch to has_capability_noaudit to reflect a more appropriate check.
> > > 
> > > Signed-off-by: Mark Salyzyn <salyzyn@...roid.com>
> > > Cc: linux-security-module@...r.kernel.org
> > > Cc: kernel-team@...roid.com
> > > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > > Cc: stable@...r.kernel.org # v3.18
> > > Fixes: upstream a082c6f680da ("ovl: filter trusted xattr for non-admin")
> > > Fixes: 3.18 4bcc9b4b3a0a ("ovl: filter trusted xattr for non-admin")
> > > ---
> > > Replaced ns_capable_noaudit with 3.18.y tree specific
> > > has_capability_noaudit present in original submission to kernel.org
> > > commit 5c2e9f346b815841f9bed6029ebcb06415caf640
> > > ("ovl: filter of trusted xattr results in audit")
> > > 
> > >  fs/overlayfs/inode.c | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
> > > index a01ec1836a72..1175efa5e956 100644
> > > --- a/fs/overlayfs/inode.c
> > > +++ b/fs/overlayfs/inode.c
> > > @@ -265,7 +265,8 @@ static bool ovl_can_list(const char *s)
> > >  		return true;
> > >  
> > >  	/* Never list trusted.overlay, list other trusted for superuser only */
> > > -	return !ovl_is_private_xattr(s) && capable(CAP_SYS_ADMIN);
> > > +	return !ovl_is_private_xattr(s) &&
> > > +	       has_capability_noaudit(current, CAP_SYS_ADMIN);
> > >  }
> > >  
> > >  ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
> > > -- 
> > > 2.23.0.581.g78d2f28ef7-goog
> > > 
> > 
> > Thanks for the backport, this one worked!
> 
> I spoke too soon:
> 
> ERROR: "has_capability_noaudit" [fs/overlayfs/overlay.ko] undefined!
> 
> That function isn't exported for modules :(

But, if this really is needed, and it fixes the issue, I'll go export
that symbol with EXPORT_SYMBOL_GPL() to fix the problem.  Any
objections?

thanks,

greg k-h