block: Fix wrong offset in bio_truncate()

bio_truncate() clears the buffer outside of last block of bdev, however
current bio_truncate() is using the wrong offset of page. So it can
return the uninitialized data.

This happened when both of truncated/corrupted FS and userspace (via
bdev) are trying to read the last of bdev.

Reported-by: syzbot+ac94ae5f68b84197f41c@syzkaller.appspotmail.com
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/875yqt1c9g.fsf@mail.parknet.co.jp
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/bio.c b/block/bio.c
index 0d400ba..4312a80 100644 (file)
--- a/block/bio.c
+++ b/block/bio.c
@@ -569,7 +569,8 @@ static void bio_truncate(struct bio *bio, unsigned new_size)
                                offset = new_size - done;
                        else
                                offset = 0;
-                       zero_user(bv.bv_page, offset, bv.bv_len - offset);
+                       zero_user(bv.bv_page, bv.bv_offset + offset,
+                                 bv.bv_len - offset);
                        truncated = true;
                }
                done += bv.bv_len;