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Subject: Re: [RFC 2/3] blktrace: fix debugfs use after free
To:     Luis Chamberlain <mcgrof@kernel.org>, axboe@kernel.dk,
        viro@zeniv.linux.org.uk, gregkh@linuxfoundation.org,
        rostedt@goodmis.org, mingo@redhat.com, jack@suse.cz,
        ming.lei@redhat.com, nstange@suse.de
Cc:     mhocko@suse.com, linux-block@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        Bart Van Assche <bvanassche@acm.org>,
        Omar Sandoval <osandov@fb.com>,
        Hannes Reinecke <hare@suse.com>,
        Michal Hocko <mhocko@kernel.org>,
        syzbot+603294af2d01acfdd6da@syzkaller.appspotmail.com
References: <20200402000002.7442-1-mcgrof@kernel.org>
 <20200402000002.7442-3-mcgrof@kernel.org>
From:   Eric Sandeen <sandeen@sandeen.net>
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Message-ID: <9a6576cf-b89d-d1af-2d74-652878cb78c8@sandeen.net>
Date:   Wed, 1 Apr 2020 20:57:42 -0500
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On 4/1/20 7:00 PM, Luis Chamberlain wrote:
> On commit 6ac93117ab00 ("blktrace: use existing disk debugfs directory")
> Omar fixed the original blktrace code for multiqueue use. This however
> left in place a possible crash, if you happen to abuse blktrace in a way
> it was not intended.
> 
> Namely, if you loop adding a device, setup the blktrace with BLKTRACESETUP,
> forget to BLKTRACETEARDOWN, and then just remove the device you end up
> with a panic:

Weird, I swear I tested that and didn't hit it, but ...
 

> This issue can be reproduced with break-blktrace [2] using:
> 
>   break-blktrace -c 10 -d

+ -s, right?
 
> This patch fixes this issue. Note that there is also another
> respective UAF but from the ioctl path [3], this should also fix
> that issue.
> 
> This patch then also contends the severity of CVE-2019-19770 as
> this issue is only possible using root to shoot yourself in the
> foot by also misuing blktrace.
> 
> [0] https://bugzilla.kernel.org/show_bug.cgi?id=205713
> [1] https://nvd.nist.gov/vuln/detail/CVE-2019-19770
> [2] https://github.com/mcgrof/break-blktrace

I verified that this does reproduce the exact same KASAN splat on
kernel 4.19.83 as reported in the original bug, thanks!

-Eric