nfsd: decouple the xprtsec policy check from check_nfsd_access()

A while back I had reported that an NFSv3 client could successfully
mount using '-o xprtsec=none' an export that had been exported with
'xprtsec=tls:mtls'.  By "successfully" I mean that the mount command
would succeed and the mount would show up in /proc/mount.  Attempting
to do anything futher with the mount would be met with NFS3ERR_ACCES.

This was fixed (albeit accidentally) by commit bb4f07f2409c ("nfsd:
Fix NFSD_MAY_BYPASS_GSS and NFSD_MAY_BYPASS_GSS_ON_ROOT") and was
subsequently re-broken by commit 0813c5f01249 ("nfsd: fix access
checking for NLM under XPRTSEC policies").

Transport Layer Security isn't an RPC security flavor or pseudo-flavor,
so we shouldn't be conflating them when determining whether the access
checks can be bypassed.  Split check_nfsd_access() into two helpers, and
have __fh_verify() call the helpers directly since __fh_verify() has
logic that allows one or both of the checks to be skipped.  All other
sites will continue to call check_nfsd_access().

Link: https://lore.kernel.org/linux-nfs/ZjO3Qwf_G87yNXb2@aion/
Fixes: 9280c5774314 ("NFSD: Handle new xprtsec= export option")
Cc: stable@vger.kernel.org
Signed-off-by: Scott Mayhew <smayhew@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

1 files changed, 57 insertions, 25 deletions

diff --git a/fs/nfsd/export.c b/fs/nfsd/export.c
index cadfc2bae60e..95b5681152c4 100644
--- a/fs/nfsd/export.c
+++ b/fs/nfsd/export.c
@@ -1082,50 +1082,62 @@ static struct svc_export *exp_find(struct cache_detail *cd,
 }
 
 /**
- * check_nfsd_access - check if access to export is allowed.
+ * check_xprtsec_policy - check if access to export is allowed by the
+ *			  xprtsec policy
  * @exp: svc_export that is being accessed.
- * @rqstp: svc_rqst attempting to access @exp (will be NULL for LOCALIO).
- * @may_bypass_gss: reduce strictness of authorization check
+ * @rqstp: svc_rqst attempting to access @exp.
+ *
+ * Helper function for check_nfsd_access().  Note that callers should be
+ * using check_nfsd_access() instead of calling this function directly.  The
+ * one exception is __fh_verify() since it has logic that may result in one
+ * or both of the helpers being skipped.
  *
  * Return values:
  *   %nfs_ok if access is granted, or
  *   %nfserr_wrongsec if access is denied
  */
-__be32 check_nfsd_access(struct svc_export *exp, struct svc_rqst *rqstp,
-			 bool may_bypass_gss)
+__be32 check_xprtsec_policy(struct svc_export *exp, struct svc_rqst *rqstp)
 {
-	struct exp_flavor_info *f, *end = exp->ex_flavors + exp->ex_nflavors;
-	struct svc_xprt *xprt;
-
-	/*
-	 * If rqstp is NULL, this is a LOCALIO request which will only
-	 * ever use a filehandle/credential pair for which access has
-	 * been affirmed (by ACCESS or OPEN NFS requests) over the
-	 * wire. So there is no need for further checks here.
-	 */
-	if (!rqstp)
-		return nfs_ok;
-
-	xprt = rqstp->rq_xprt;
+	struct svc_xprt *xprt = rqstp->rq_xprt;
 
 	if (exp->ex_xprtsec_modes & NFSEXP_XPRTSEC_NONE) {
 		if (!test_bit(XPT_TLS_SESSION, &xprt->xpt_flags))
-			goto ok;
+			return nfs_ok;
 	}
 	if (exp->ex_xprtsec_modes & NFSEXP_XPRTSEC_TLS) {
 		if (test_bit(XPT_TLS_SESSION, &xprt->xpt_flags) &&
 		    !test_bit(XPT_PEER_AUTH, &xprt->xpt_flags))
-			goto ok;
+			return nfs_ok;
 	}
 	if (exp->ex_xprtsec_modes & NFSEXP_XPRTSEC_MTLS) {
 		if (test_bit(XPT_TLS_SESSION, &xprt->xpt_flags) &&
 		    test_bit(XPT_PEER_AUTH, &xprt->xpt_flags))
-			goto ok;
+			return nfs_ok;
 	}
-	if (!may_bypass_gss)
-		goto denied;
+	return nfserr_wrongsec;
+}
+
+/**
+ * check_security_flavor - check if access to export is allowed by the
+ *			   security flavor
+ * @exp: svc_export that is being accessed.
+ * @rqstp: svc_rqst attempting to access @exp.
+ * @may_bypass_gss: reduce strictness of authorization check
+ *
+ * Helper function for check_nfsd_access().  Note that callers should be
+ * using check_nfsd_access() instead of calling this function directly.  The
+ * one exception is __fh_verify() since it has logic that may result in one
+ * or both of the helpers being skipped.
+ *
+ * Return values:
+ *   %nfs_ok if access is granted, or
+ *   %nfserr_wrongsec if access is denied
+ */
+__be32 check_security_flavor(struct svc_export *exp, struct svc_rqst *rqstp,
+			     bool may_bypass_gss)
+{
+	struct exp_flavor_info *f, *end = exp->ex_flavors + exp->ex_nflavors;
 
-ok:
 	/* legacy gss-only clients are always OK: */
 	if (exp->ex_client == rqstp->rq_gssclient)
 		return nfs_ok;
@@ -1167,10 +1179,30 @@ ok:
 		}
 	}
 
-denied:
 	return nfserr_wrongsec;
 }
 
+/**
+ * check_nfsd_access - check if access to export is allowed.
+ * @exp: svc_export that is being accessed.
+ * @rqstp: svc_rqst attempting to access @exp.
+ * @may_bypass_gss: reduce strictness of authorization check
+ *
+ * Return values:
+ *   %nfs_ok if access is granted, or
+ *   %nfserr_wrongsec if access is denied
+ */
+__be32 check_nfsd_access(struct svc_export *exp, struct svc_rqst *rqstp,
+			 bool may_bypass_gss)
+{
+	__be32 status;
+
+	status = check_xprtsec_policy(exp, rqstp);
+	if (status != nfs_ok)
+		return status;
+	return check_security_flavor(exp, rqstp, may_bypass_gss);
+}
+
 /*
  * Uses rq_client and rq_gssclient to find an export; uses rq_client (an
  * auth_unix client) if it's available and has secinfo information;