[RFC PATCH 1/6] sunrpc: Tighten bounds checking in svc_rqst_replace_page

[Chuck Lever <cel@kernel.org>]

From: Chuck Lever <chuck.lever@oracle.com>

svc_rqst_replace_page() builds the Reply buffer by advancing
rq_next_page through the response page range. The bounds
check validates rq_next_page against the full rq_pages array,
but the valid range for rq_next_page is
[rq_respages, rq_page_end]. Use those bounds instead.

This is correct today because rq_respages and rq_page_end
both point into rq_pages, and it prepares for a subsequent
change that separates the Reply page array from rq_pages.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 net/sunrpc/svc.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 346ac560dcc2..05ba4040a24a 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -935,11 +935,11 @@ svc_set_num_threads(struct svc_serv *serv, unsigned int min_threads,
 EXPORT_SYMBOL_GPL(svc_set_num_threads);
 
 /**
- * svc_rqst_replace_page - Replace one page in rq_pages[]
+ * svc_rqst_replace_page - Replace one page in rq_respages[]
  * @rqstp: svc_rqst with pages to replace
  * @page: replacement page
  *
- * When replacing a page in rq_pages, batch the release of the
+ * When replacing a page in rq_respages, batch the release of the
  * replaced pages to avoid hammering the page allocator.
  *
  * Return values:
@@ -948,8 +948,8 @@ EXPORT_SYMBOL_GPL(svc_set_num_threads);
  */
 bool svc_rqst_replace_page(struct svc_rqst *rqstp, struct page *page)
 {
-	struct page **begin = rqstp->rq_pages;
-	struct page **end = &rqstp->rq_pages[rqstp->rq_maxpages];
+	struct page **begin = rqstp->rq_respages;
+	struct page **end = rqstp->rq_page_end;
 
 	if (unlikely(rqstp->rq_next_page < begin || rqstp->rq_next_page > end)) {
 		trace_svc_replace_page_err(rqstp);
-- 
2.53.0