ext4: handle EOF correctly in ext4_bio_write_page()

We need to zero out part of a page which beyond EOF before setting uptodate,
otherwise, mapread or write will see non-zero data beyond EOF.

Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@kernel.org

1 files changed, 12 insertions, 0 deletions

diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index 7ce1d0b19c94..7e106c810c62 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -385,6 +385,18 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
 
                 block_end = block_start + blocksize;
                 if (block_start >= len) {
+                        /*
+                         * Comments copied from block_write_full_page_endio:
+                         *
+                         * The page straddles i_size.  It must be zeroed out on
+                         * each and every writepage invocation because it may
+                         * be mmapped.  "A file is mapped in multiples of the
+                         * page size.  For a file that is not a multiple of
+                         * the  page size, the remaining memory is zeroed when
+                         * mapped, and writes to that region are not written
+                         * out to the file."
+                         */
+                        zero_user_segment(page, block_start, block_end);
                         clear_buffer_dirty(bh);
                         set_buffer_uptodate(bh);
                         continue;