[PATCH 5.4 018/348] copy_page_to_iter(): fix ITER_DISCARD case

[Greg Kroah-Hartman]

From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>

commit a506abc7b644d71966a75337d5a534f531b3cdc4 upstream.

we need to advance the iterator...

Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 lib/iov_iter.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -896,9 +896,12 @@ size_t copy_page_to_iter(struct page *pa
 		size_t wanted = copy_to_iter(kaddr + offset, bytes, i);
 		kunmap_atomic(kaddr);
 		return wanted;
-	} else if (unlikely(iov_iter_is_discard(i)))
+	} else if (unlikely(iov_iter_is_discard(i))) {
+		if (unlikely(i->count < bytes))
+			bytes = i->count;
+		i->count -= bytes;
 		return bytes;
-	else if (likely(!iov_iter_is_pipe(i)))
+	} else if (likely(!iov_iter_is_pipe(i)))
 		return copy_page_to_iter_iovec(page, offset, bytes, i);
 	else
 		return copy_page_to_iter_pipe(page, offset, bytes, i);