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>

5 files changed, 33 insertions, 18 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
diff --git a/fs/nfsd/nfsfh.c b/fs/nfsd/nfsfh.c
index ea37c96f0445..cd25d91895a1 100644
--- a/fs/nfsd/nfsfh.c
+++ b/fs/nfsd/nfsfh.c
@@ -302,17 +302,27 @@ fh_verify(struct svc_rqst *rqstp, struct svc_fh *fhp, int type, int access)
         if (error)
                 goto out;
 
-        if (!(access & NFSD_MAY_LOCK)) {
-                /*
-                 * pseudoflavor restrictions are not enforced on NLM,
-                 * which clients virtually always use auth_sys for,
-                 * even while using RPCSEC_GSS for NFS.
-                 */
-                error = check_nfsd_access(exp, rqstp);
-                if (error)
-                        goto out;
-        }
+        /*
+         * pseudoflavor restrictions are not enforced on NLM,
+         * which clients virtually always use auth_sys for,
+         * even while using RPCSEC_GSS for NFS.
+         */
+        if (access & NFSD_MAY_LOCK)
+                goto skip_pseudoflavor_check;
+        /*
+         * Clients may expect to be able to use auth_sys during mount,
+         * even if they use gss for everything else; see section 2.3.2
+         * of rfc 2623.
+         */
+        if (access & NFSD_MAY_BYPASS_GSS_ON_ROOT
+                        && exp->ex_path.dentry == dentry)
+                goto skip_pseudoflavor_check;
+
+        error = check_nfsd_access(exp, rqstp);
+        if (error)
+                goto out;
 
+skip_pseudoflavor_check:
         /* Finally, check access permissions. */
         error = nfsd_permission(rqstp, exp, dentry, access);
 
diff --git a/fs/nfsd/nfsproc.c b/fs/nfsd/nfsproc.c
index 0766f95d236a..5cffeca7acef 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;
 }
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 18060bed5267..1319e8027d55 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1866,9 +1866,9 @@ out:
  * N.B. After this call fhp needs an fh_put
  */
 __be32
-nfsd_statfs(struct svc_rqst *rqstp, struct svc_fh *fhp, struct kstatfs *stat)
+nfsd_statfs(struct svc_rqst *rqstp, struct svc_fh *fhp, struct kstatfs *stat, int access)
 {
-        __be32 err = fh_verify(rqstp, fhp, 0, NFSD_MAY_NOP);
+        __be32 err = fh_verify(rqstp, fhp, 0, NFSD_MAY_NOP | access);
         if (!err && vfs_statfs(fhp->fh_dentry,stat))
                 err = nfserr_io;
         return err;
diff --git a/include/linux/nfsd/nfsd.h b/include/linux/nfsd/nfsd.h
index 108f47e5fd95..21269405ffe2 100644
--- a/include/linux/nfsd/nfsd.h
+++ b/include/linux/nfsd/nfsd.h
@@ -38,6 +38,7 @@
 #define NFSD_MAY_LOCK           32
 #define NFSD_MAY_OWNER_OVERRIDE 64
 #define NFSD_MAY_LOCAL_ACCESS   128 /* IRIX doing local access check on device special file*/
+#define NFSD_MAY_BYPASS_GSS_ON_ROOT 256
 
 #define NFSD_MAY_CREATE         (NFSD_MAY_EXEC|NFSD_MAY_WRITE)
 #define NFSD_MAY_REMOVE         (NFSD_MAY_EXEC|NFSD_MAY_WRITE|NFSD_MAY_TRUNC)
@@ -125,7 +126,7 @@ int		nfsd_truncate(struct svc_rqst *, struct svc_fh *,
 __be32          nfsd_readdir(struct svc_rqst *, struct svc_fh *,
                              loff_t *, struct readdir_cd *, filldir_t);
 __be32          nfsd_statfs(struct svc_rqst *, struct svc_fh *,
-                                struct kstatfs *);
+                                struct kstatfs *, int access);
 
 int             nfsd_notify_change(struct inode *, struct iattr *);
 __be32          nfsd_permission(struct svc_rqst *, struct svc_export *,