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

[Greg Kroah-Hartman]

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@xxxxxxxxxxx>
> > Cc: linux-security-module@xxxxxxxxxxxxxxx
> > Cc: kernel-team@xxxxxxxxxxx
> > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx # 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 :(

greg k-h