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, 5 insertions, 3 deletions

diff --git a/fs/nfsd/nfs3proc.c b/fs/nfsd/nfs3proc.c
index 4d617ea28cfc..9dbd2eb91281 100644
--- a/fs/nfsd/nfs3proc.c
+++ b/fs/nfsd/nfs3proc.c
@@ -63,7 +63,8 @@ nfsd3_proc_getattr(struct svc_rqst *rqstp, struct nfsd_fhandle  *argp,
                 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);
         if (nfserr)
                 RETURN_STATUS(nfserr);
 
@@ -530,7 +531,7 @@ nfsd3_proc_fsstat(struct svc_rqst * rqstp, struct nfsd_fhandle    *argp,
         dprintk("nfsd: FSSTAT(3)   %s\n",
                                 SVCFH_fmt(&argp->fh));
 
-        nfserr = nfsd_statfs(rqstp, &argp->fh, &resp->stats);
+        nfserr = nfsd_statfs(rqstp, &argp->fh, &resp->stats, 0);
         fh_put(&argp->fh);
         RETURN_STATUS(nfserr);
 }
@@ -558,7 +559,8 @@ nfsd3_proc_fsinfo(struct svc_rqst * rqstp, struct nfsd_fhandle    *argp,
         resp->f_maxfilesize = ~(u32) 0;
         resp->f_properties = NFS3_FSF_DEFAULT;
 
-        nfserr = fh_verify(rqstp, &argp->fh, 0, NFSD_MAY_NOP);
+        nfserr = fh_verify(rqstp, &argp->fh, 0,
+                        NFSD_MAY_NOP | NFSD_MAY_BYPASS_GSS_ON_ROOT);
 
         /* Check special features of the file system. May request
          * different read/write sizes for file systems known to have