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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        syzbot+ac94ae5f68b84197f41c@syzkaller.appspotmail.com,
        OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>,
        Ming Lei <ming.lei@redhat.com>, Jens Axboe <axboe@kernel.dk>
Subject: [PATCH 5.4 64/64] block: Fix wrong offset in bio_truncate()
Date:   Mon, 31 Jan 2022 11:56:49 +0100
Message-Id: <20220131105217.821837502@linuxfoundation.org>
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From: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>

commit 3ee859e384d453d6ac68bfd5971f630d9fa46ad3 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 block/bio.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/block/bio.c
+++ b/block/bio.c
@@ -569,7 +569,8 @@ 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;