linux-kernel - Re: [RFC 0/3] block: address blktrace use-after-free

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Date:   Fri, 3 Apr 2020 16:19:29 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     axboe@...nel.dk, viro@...iv.linux.org.uk,
        gregkh@...uxfoundation.org, rostedt@...dmis.org, mingo@...hat.com,
        jack@...e.cz, nstange@...e.de, mhocko@...e.com,
        linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, yukuai3@...wei.com
Subject: Re: [RFC 0/3] block: address blktrace use-after-free

On Wed, Apr 01, 2020 at 11:59:59PM +0000, Luis Chamberlain wrote:
> Upstream kernel.org korg#205713 contends that there is a UAF in
> the core debugfs debugfs_remove() function, and has gone through
> pushing for a CVE for this, CVE-2019-19770.
> 
> If correct then parent dentries are not positive, and this would
> have implications far beyond this bug report. Thankfully, upon review
> with Nicolai, he wasn't buying it. His suspicions that this was just
> a blktrace issue were spot on, and this patch series demonstrates
> that, provides a reproducer, and provides a solution to the issue.
> 
> We there would like to contend CVE-2019-19770 as invalid. The
> implications suggested are not correct, and this issue is only
> triggerable with root, by shooting yourself on the foot by misuing
> blktrace.
> 
> If you want this on a git tree, you can get it from linux-next
> 20200401-blktrace-fix-uaf branch [2].
> 
> Wider review, testing, and rants are appreciated.
> 
> [0] https://bugzilla.kernel.org/show_bug.cgi?id=205713
> [1] https://nvd.nist.gov/vuln/detail/CVE-2019-19770
> [2] https://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux-next.git/log/?h=20200401-blktrace-fix-uaf
> 
> Luis Chamberlain (3):
>   block: move main block debugfs initialization to its own file
>   blktrace: fix debugfs use after free
>   block: avoid deferral of blk_release_queue() work
> 
>  block/Makefile               |  1 +
>  block/blk-core.c             |  9 +--------
>  block/blk-debugfs.c          | 27 +++++++++++++++++++++++++++
>  block/blk-mq-debugfs.c       |  5 -----
>  block/blk-sysfs.c            | 21 ++++++++-------------
>  block/blk.h                  | 17 +++++++++++++++++
>  include/linux/blktrace_api.h |  1 -
>  kernel/trace/blktrace.c      | 19 ++++++++-----------
>  8 files changed, 62 insertions(+), 38 deletions(-)
>  create mode 100644 block/blk-debugfs.c

BTW, Yu Kuai posted one patch for this issue, looks that approach
is simpler:

https://lore.kernel.org/linux-block/20200324132315.22133-1-yukuai3@huawei.com/


Thanks,
Ming