nfsd4: adjust buflen to session channel limit

We can simplify session limit enforcement by restricting the xdr buflen
to the session size.

Also fix a preexisting bug: we should really have been taking into
account the auth-required space when comparing against session limits,
which are limits on the size of the entire rpc reply, including any krb5
overhead.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>

2 files changed, 19 insertions, 16 deletions

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 8e22ea485f99..612b85ac414b 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -2208,11 +2208,13 @@ nfsd4_sequence(struct svc_rqst *rqstp,
                struct nfsd4_sequence *seq)
 {
         struct nfsd4_compoundres *resp = rqstp->rq_resp;
+        struct xdr_stream *xdr = &resp->xdr;
         struct nfsd4_session *session;
         struct nfs4_client *clp;
         struct nfsd4_slot *slot;
         struct nfsd4_conn *conn;
         __be32 status;
+        int buflen;
         struct nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
 
         if (resp->opcnt != 1)
@@ -2281,6 +2283,15 @@ nfsd4_sequence(struct svc_rqst *rqstp,
         if (status)
                 goto out_put_session;
 
+        buflen = (seq->cachethis) ?
+                        session->se_fchannel.maxresp_cached :
+                        session->se_fchannel.maxresp_sz;
+        status = (seq->cachethis) ? nfserr_rep_too_big_to_cache :
+                                    nfserr_rep_too_big;
+        if (xdr_restrict_buflen(xdr, buflen - 2 * RPC_MAX_AUTH_SIZE))
+                goto out_put_session;
+
+        status = nfs_ok;
         /* Success! bump slot seqid */
         slot->sl_seqid = seq->seqid;
         slot->sl_flags |= NFSD4_SLOT_INUSE;
diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 1278d98a923c..5e7bac4a7e71 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -3767,25 +3767,17 @@ static nfsd4_enc nfsd4_enc_ops[] = {
 __be32 nfsd4_check_resp_size(struct nfsd4_compoundres *resp, u32 respsize)
 {
         struct xdr_buf *buf = &resp->rqstp->rq_res;
-        struct nfsd4_session *session = resp->cstate.session;
+        struct nfsd4_slot *slot = resp->cstate.slot;
 
-        if (nfsd4_has_session(&resp->cstate)) {
-                struct nfsd4_slot *slot = resp->cstate.slot;
-
-                if (buf->len + respsize > session->se_fchannel.maxresp_sz)
-                        return nfserr_rep_too_big;
-
-                if ((slot->sl_flags & NFSD4_SLOT_CACHETHIS) &&
-                    buf->len + respsize > session->se_fchannel.maxresp_cached)
-                        return nfserr_rep_too_big_to_cache;
-        }
-
-        if (buf->len + respsize > buf->buflen) {
-                WARN_ON_ONCE(nfsd4_has_session(&resp->cstate));
+        if (buf->len + respsize <= buf->buflen)
+                return nfs_ok;
+        if (!nfsd4_has_session(&resp->cstate))
                 return nfserr_resource;
+        if (slot->sl_flags & NFSD4_SLOT_CACHETHIS) {
+                WARN_ON_ONCE(1);
+                return nfserr_rep_too_big_to_cache;
         }
-
-        return 0;
+        return nfserr_rep_too_big;
 }
 
 void