copy_page_to_iter(): fix ITER_DISCARD case

we need to advance the iterator...

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

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 12fb04b..c8877cf 100644 (file)
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -965,9 +965,12 @@ static size_t __copy_page_to_iter(struct page *page, size_t offset, size_t bytes
                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);