[PATCH] block: Fix wrong offset in bio_truncate()

[OGAWA Hirofumi]

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@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>
---
 block/bio.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/bio.c b/block/bio.c
index a6fb6a0..25f1ed2 100644
--- a/block/bio.c	2021-11-01 09:19:05.999472589 +0900
+++ b/block/bio.c	2022-01-09 17:40:09.010438012 +0900
@@ -567,7 +567,8 @@ void bio_truncate(struct bio *bio, unsig
 				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;
_

-- 
OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>