[PATCH] knfsd: nfsd4: fix corruption on readdir encoding with 64k pages

Fix corruption on readdir encoding with 64k pages.
Signed-off-by: NJ. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: NNeil Brown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

fs/nfsd/nfs4xdr.c

@@ -2157,7 +2157,7 @@ nfsd4_encode_readdir(struct nfsd4_compoundres *resp, int nfserr, struct nfsd4_re
 {
 	int maxcount;
 	loff_t offset;
-	u32 *page, *savep;
+	u32 *page, *savep, *tailbase;
 	ENCODE_HEAD;
 
 	if (nfserr)
@@ -2173,6 +2173,7 @@ nfsd4_encode_readdir(struct nfsd4_compoundres *resp, int nfserr, struct nfsd4_re
 	WRITE32(0);
 	ADJUST_ARGS();
 	resp->xbuf->head[0].iov_len = ((char*)resp->p) - (char*)resp->xbuf->head[0].iov_base;
+	tailbase = p;
 
 	maxcount = PAGE_SIZE;
 	if (maxcount > readdir->rd_maxcount)
@@ -2217,14 +2218,12 @@ nfsd4_encode_readdir(struct nfsd4_compoundres *resp, int nfserr, struct nfsd4_re
 	*p++ = htonl(readdir->common.err == nfserr_eof);
 	resp->xbuf->page_len = ((char*)p) - (char*)page_address(resp->rqstp->rq_respages[resp->rqstp->rq_resused-1]);
 
-	/* allocate a page for the tail */
-	svc_take_page(resp->rqstp);
-	resp->xbuf->tail[0].iov_base = 
-		page_address(resp->rqstp->rq_respages[resp->rqstp->rq_resused-1]);
-	resp->rqstp->rq_restailpage = resp->rqstp->rq_resused-1;
+	/* Use rest of head for padding and remaining ops: */
+	resp->rqstp->rq_restailpage = 0;
+	resp->xbuf->tail[0].iov_base = tailbase;
 	resp->xbuf->tail[0].iov_len = 0;
 	resp->p = resp->xbuf->tail[0].iov_base;
-	resp->end = resp->p + PAGE_SIZE/4;
+	resp->end = resp->p + (PAGE_SIZE - resp->xbuf->head[0].iov_len)/4;
 
 	return 0;
 err_no_verf: