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>

diff --git a/fs/nfsd/export.c b/fs/nfsd/export.c
index cadfc2bae60ea14a90a85c29026a0b7603080531..95b5681152c47afa5313f5e1f06132225d4c35f0 100644 (file)
--- 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;

diff --git a/fs/nfsd/export.h b/fs/nfsd/export.h
index b9c0adb3ce09186695f6ec4164ccbf550309a4c4..ef5581911d5b875945451e39e5951e327bfb6021 100644 (file)
--- a/fs/nfsd/export.h
+++ b/fs/nfsd/export.h
@@ -101,6 +101,9 @@ struct svc_expkey {
 
 struct svc_cred;
 int nfsexp_flags(struct svc_cred *cred, struct svc_export *exp);
+__be32 check_xprtsec_policy(struct svc_export *exp, struct svc_rqst *rqstp);
+__be32 check_security_flavor(struct svc_export *exp, struct svc_rqst *rqstp,
+                            bool may_bypass_gss);
 __be32 check_nfsd_access(struct svc_export *exp, struct svc_rqst *rqstp,
                         bool may_bypass_gss);
 

diff --git a/fs/nfsd/nfsfh.c b/fs/nfsd/nfsfh.c
index f4c2fb3dd5d05f7f8fef0d9af74e0b3fe4009873..062cfc18d8c6a4cb29465a482cb575a85a1e5691 100644 (file)
--- a/fs/nfsd/nfsfh.c
+++ b/fs/nfsd/nfsfh.c
@@ -364,10 +364,30 @@ __fh_verify(struct svc_rqst *rqstp,
        if (error)
                goto out;
 
+       /*
+        * 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.  Skip both the xprtsec policy and the security flavor
+        * checks.
+        */
+       if (!rqstp)
+               goto check_permissions;
+
        if ((access & NFSD_MAY_NLM) && (exp->ex_flags & NFSEXP_NOAUTHNLM))
                /* NLM is allowed to fully bypass authentication */
                goto out;
 
+       /*
+        * NLM is allowed to bypass the xprtsec policy check because lockd
+        * doesn't support xprtsec.
+        */
+       if (!(access & NFSD_MAY_NLM)) {
+               error = check_xprtsec_policy(exp, rqstp);
+               if (error)
+                       goto out;
+       }
+
        if (access & NFSD_MAY_BYPASS_GSS)
                may_bypass_gss = true;
        /*
@@ -379,13 +399,15 @@ __fh_verify(struct svc_rqst *rqstp,
                        && exp->ex_path.dentry == dentry)
                may_bypass_gss = true;
 
-       error = check_nfsd_access(exp, rqstp, may_bypass_gss);
+       error = check_security_flavor(exp, rqstp, may_bypass_gss);
        if (error)
                goto out;
+
        /* During LOCALIO call to fh_verify will be called with a NULL rqstp */
        if (rqstp)
                svc_xprt_set_valid(rqstp->rq_xprt);
 
+check_permissions:
        /* Finally, check access permissions. */
        error = nfsd_permission(cred, exp, dentry, access);
 out: