svcrdma: bound check rq_pages index in inline path

svc_rdma_copy_inline_range indexed rqstp->rq_pages[rc_curpage] without
verifying rc_curpage stays within the allocated page array. Add guards
before the first use and after advancing to a new page.

Fixes: d7cc73972661 ("svcrdma: support multiple Read chunks per RPC")
Cc: [e-mail]
Signed-off-by: Joshua Rogers <[e-mail]>
Signed-off-by: Chuck Lever <[e-mail]>

net/sunrpc/xprtrdma/svc_rdma_rw.c

···
 	for (page_no = 0; page_no < numpages; page_no++) {
 		unsigned int page_len;
 
+		if (head->rc_curpage >= rqstp->rq_maxpages)
+			return -EINVAL;
+
 		page_len = min_t(unsigned int, remaining,
 				 PAGE_SIZE - head->rc_pageoff);