gss_krb5: Added and improved code comments

Signed-off-by: Steve Dickson <steved@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

3 files changed, 38 insertions, 3 deletions

diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c
index 75602ece58eb..d64a58b8ed33 100644
--- a/net/sunrpc/auth_gss/auth_gss.c
+++ b/net/sunrpc/auth_gss/auth_gss.c
@@ -1316,15 +1316,21 @@ gss_wrap_req_priv(struct rpc_cred *cred, struct gss_cl_ctx *ctx,
         inpages = snd_buf->pages + first;
         snd_buf->pages = rqstp->rq_enc_pages;
         snd_buf->page_base -= first << PAGE_CACHE_SHIFT;
-        /* Give the tail its own page, in case we need extra space in the
-         * head when wrapping: */
+        /*
+         * Give the tail its own page, in case we need extra space in the
+         * head when wrapping:
+         *
+         * call_allocate() allocates twice the slack space required
+         * by the authentication flavor to rq_callsize.
+         * For GSS, slack is GSS_CRED_SLACK.
+         */
         if (snd_buf->page_len || snd_buf->tail[0].iov_len) {
                 tmp = page_address(rqstp->rq_enc_pages[rqstp->rq_enc_pages_num - 1]);
                 memcpy(tmp, snd_buf->tail[0].iov_base, snd_buf->tail[0].iov_len);
                 snd_buf->tail[0].iov_base = tmp;
         }
         maj_stat = gss_wrap(ctx->gc_gss_ctx, offset, snd_buf, inpages);
-        /* RPC_SLACK_SPACE should prevent this ever happening: */
+        /* slack space should prevent this ever happening: */
         BUG_ON(snd_buf->len > snd_buf->buflen);
         status = -EIO;
         /* We're assuming that when GSS_S_CONTEXT_EXPIRED, the encryption was
diff --git a/net/sunrpc/auth_gss/gss_mech_switch.c b/net/sunrpc/auth_gss/gss_mech_switch.c
index 76e4c6f4ac3c..28a84ef41d13 100644
--- a/net/sunrpc/auth_gss/gss_mech_switch.c
+++ b/net/sunrpc/auth_gss/gss_mech_switch.c
@@ -285,6 +285,20 @@ gss_verify_mic(struct gss_ctx		*context_handle,
                                  mic_token);
 }
 
+/*
+ * This function is called from both the client and server code.
+ * Each makes guarantees about how much "slack" space is available
+ * for the underlying function in "buf"'s head and tail while
+ * performing the wrap.
+ *
+ * The client and server code allocate RPC_MAX_AUTH_SIZE extra
+ * space in both the head and tail which is available for use by
+ * the wrap function.
+ *
+ * Underlying functions should verify they do not use more than
+ * RPC_MAX_AUTH_SIZE of extra space in either the head or tail
+ * when performing the wrap.
+ */
 u32
 gss_wrap(struct gss_ctx *ctx_id,
          int            offset,
diff --git a/net/sunrpc/auth_gss/svcauth_gss.c b/net/sunrpc/auth_gss/svcauth_gss.c
index b81e790ef9f4..1d9ac4ac818a 100644
--- a/net/sunrpc/auth_gss/svcauth_gss.c
+++ b/net/sunrpc/auth_gss/svcauth_gss.c
@@ -1315,6 +1315,14 @@ svcauth_gss_wrap_resp_priv(struct svc_rqst *rqstp)
         inpages = resbuf->pages;
         /* XXX: Would be better to write some xdr helper functions for
          * nfs{2,3,4}xdr.c that place the data right, instead of copying: */
+
+        /*
+         * If there is currently tail data, make sure there is
+         * room for the head, tail, and 2 * RPC_MAX_AUTH_SIZE in
+         * the page, and move the current tail data such that
+         * there is RPC_MAX_AUTH_SIZE slack space available in
+         * both the head and tail.
+         */
         if (resbuf->tail[0].iov_base) {
                 BUG_ON(resbuf->tail[0].iov_base >= resbuf->head[0].iov_base
                                                         + PAGE_SIZE);
@@ -1327,6 +1335,13 @@ svcauth_gss_wrap_resp_priv(struct svc_rqst *rqstp)
                         resbuf->tail[0].iov_len);
                 resbuf->tail[0].iov_base += RPC_MAX_AUTH_SIZE;
         }
+        /*
+         * If there is no current tail data, make sure there is
+         * room for the head data, and 2 * RPC_MAX_AUTH_SIZE in the
+         * allotted page, and set up tail information such that there
+         * is RPC_MAX_AUTH_SIZE slack space available in both the
+         * head and tail.
+         */
         if (resbuf->tail[0].iov_base == NULL) {
                 if (resbuf->head[0].iov_len + 2*RPC_MAX_AUTH_SIZE > PAGE_SIZE)
                         return -ENOMEM;