nfsd: permit unauthenticated stat of export root

RFC 2623 section 2.3.2 permits the server to bypass gss authentication
checks for certain operations that a client may perform when mounting.
In the case of a client that doesn't have some form of credentials
available to it on boot, this allows it to perform the mount unattended.
(Presumably real file access won't be needed until a user with
credentials logs in.)

Being slightly more lenient allows lots of old clients to access
krb5-only exports, with the only loss being a small amount of
information leaked about the root directory of the export.

This affects only v2 and v3; v4 still requires authentication for all
access.

Thanks to Peter Staubach testing against a Solaris client, which
suggesting addition of v3 getattr, to the list, and to Trond for noting
that doing so exposes no additional information.

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Cc: Peter Staubach <staubach@redhat.com>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>

1 files changed, 4 insertions, 2 deletions

diff --git a/fs/nfsd/nfsproc.c b/fs/nfsd/nfsproc.c
index 0766f95d236..5cffeca7ace 100644
--- a/fs/nfsd/nfsproc.c
+++ b/fs/nfsd/nfsproc.c
@@ -65,7 +65,8 @@ nfsd_proc_getattr(struct svc_rqst *rqstp, struct nfsd_fhandle  *argp,
 	dprintk("nfsd: GETATTR  %s\n", SVCFH_fmt(&argp->fh));
 
 	fh_copy(&resp->fh, &argp->fh);
-	nfserr = fh_verify(rqstp, &resp->fh, 0, NFSD_MAY_NOP);
+	nfserr = fh_verify(rqstp, &resp->fh, 0,
+			NFSD_MAY_NOP | NFSD_MAY_BYPASS_GSS_ON_ROOT);
 	return nfsd_return_attrs(nfserr, resp);
 }
 
@@ -521,7 +522,8 @@ nfsd_proc_statfs(struct svc_rqst * rqstp, struct nfsd_fhandle   *argp,
 
 	dprintk("nfsd: STATFS   %s\n", SVCFH_fmt(&argp->fh));
 
-	nfserr = nfsd_statfs(rqstp, &argp->fh, &resp->stats);
+	nfserr = nfsd_statfs(rqstp, &argp->fh, &resp->stats,
+			NFSD_MAY_BYPASS_GSS_ON_ROOT);
 	fh_put(&argp->fh);
 	return nfserr;
 }