linux-kernel - Re: [PATCH v2] block: Fix use-after-free in blkdev

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Message-ID: <20200605094353.GS30374@kadam>
Date:   Fri, 5 Jun 2020 12:43:54 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Jason Yan <yanaijie@...wei.com>, Jan Kara <jack@...e.cz>
Cc:     Markus Elfring <Markus.Elfring@....de>,
        linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        hulkci@...wei.com, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>,
        Ming Lei <ming.lei@...hat.com>
Subject: Re: [PATCH v2] block: Fix use-after-free in blkdev_get()

A lot of maintainers have blocked Markus and asked him to stop trying
to help people write commit message.  Saying "bdev" instead of "block
device" is more clear so your original message was better.

The Fixes tag is a good idea though:

Fixes: 89e524c04fa9 ("loop: Fix mount(2) failure due to race with LOOP_SET_FD")

It broke last July.  Before that, we used to check if __blkdev_get()
failed before dereferencing "bdev".

I wonder if maybe the best fix is to re-add the "if (!res) " check back
to blkdev_get().  The __blkdev_get() looks like it can also free "whole"
though if it calls itself recursively and I don't really know this code
so I can't say for sure...

regards,
dan carpenter