Date:   Mon, 10 Jan 2022 16:00:00 +0800
From:   Ming Lei <ming.lei@redhat.com>
To:     OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc:     linux-block@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
        glider@google.com, linux-kernel@vger.kernel.org,
        syzkaller-bugs@googlegroups.com,
        syzbot <syzbot+ac94ae5f68b84197f41c@syzkaller.appspotmail.com>
Subject: Re: [PATCH] block: Fix wrong offset in bio_truncate()
Message-ID: <YdvngICmbNXOFIIj@T590>
References: <000000000000880fca05d4fc73b0@google.com>
 <875yqt1c9g.fsf@mail.parknet.co.jp>
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On Sun, Jan 09, 2022 at 06:36:43PM +0900, OGAWA Hirofumi wrote:
> 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>
> ---
>  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);

Looks correct:

Reviewed-by: Ming Lei <ming.lei@redhat.com>

-- 
Ming