From: Al Viro <viro@zeniv.linux.org.uk>
Date: Fri, 29 Jul 2022 16:54:53 +0000 (-0400)
Subject: fix copy_page_from_iter() for compound destinations
X-Git-Tag: v6.1-rc5~645^2
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=c03f05f183cd15f4259684ab658fbc3d23797d99;p=platform%2Fkernel%2Flinux-starfive.git

fix copy_page_from_iter() for compound destinations

had been broken for ITER_BVEC et.al. since ever (OK, v3.17 when
ITER_BVEC had first appeared)...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 4e3696d..4b7fce7 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -738,13 +738,27 @@ EXPORT_SYMBOL(copy_page_to_iter);
 size_t copy_page_from_iter(struct page *page, size_t offset, size_t bytes,
 			 struct iov_iter *i)
 {
-	if (page_copy_sane(page, offset, bytes)) {
+	size_t res = 0;
+	if (!page_copy_sane(page, offset, bytes))
+		return 0;
+	page += offset / PAGE_SIZE; // first subpage
+	offset %= PAGE_SIZE;
+	while (1) {
 		void *kaddr = kmap_local_page(page);
-		size_t wanted = _copy_from_iter(kaddr + offset, bytes, i);
+		size_t n = min(bytes, (size_t)PAGE_SIZE - offset);
+		n = _copy_from_iter(kaddr + offset, n, i);
 		kunmap_local(kaddr);
-		return wanted;
+		res += n;
+		bytes -= n;
+		if (!bytes || !n)
+			break;
+		offset += n;
+		if (offset == PAGE_SIZE) {
+			page++;
+			offset = 0;
+		}
 	}
-	return 0;
+	return res;
 }
 EXPORT_SYMBOL(copy_page_from_iter);