From: Bart Van Assche <bvanassche@acm.org>
To: Luis Chamberlain <mcgrof@kernel.org>,
Christoph Hellwig <hch@infradead.org>
Cc: 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, akpm@linux-foundation.org, mhocko@suse.com,
yukuai3@huawei.com, linux-block@vger.kernel.org,
linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, Omar Sandoval <osandov@fb.com>,
Hannes Reinecke <hare@suse.com>, Michal Hocko <mhocko@kernel.org>,
syzbot+603294af2d01acfdd6da@syzkaller.appspotmail.com
Subject: Re: [PATCH v5 5/7] blktrace: fix debugfs use after free
Date: Wed, 27 May 2020 18:15:10 -0700 [thread overview]
Message-ID: <3e5e75d4-56ad-19c6-fbc3-b8c78283ec54@acm.org> (raw)
In-Reply-To: <20200527031202.GT11244@42.do-not-panic.com>
On 2020-05-26 20:12, Luis Chamberlain wrote:
> + /*
> + * Blktrace needs a debugsfs name even for queues that don't register
> + * a gendisk, so it lazily registers the debugfs directory. But that
> + * can get us into a situation where a SCSI device is found, with no
> + * driver for it (yet). Then blktrace is used on the device, creating
> + * the debugfs directory, and only after that a drivers is loaded. In
^^^^^^^
driver?
> @@ -494,6 +490,38 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
> */
> strreplace(buts->name, '/', '_');
>
> + /*
> + * We also have to use a partition directory if a partition is
> + * being worked on, even though the same request_queue is shared.
> + */
> + if (bdev && bdev != bdev->bd_contains)
> + dir = bdev->bd_part->debugfs_dir;
Please balance braces in if-statements as required by the kernel coding style.
> + else {
> + /*
> + * For queues that do not have a gendisk attached to them, the
> + * debugfs directory will not have been created at setup time.
> + * Create it here lazily, it will only be removed when the
> + * queue is torn down.
> + */
Is the above comment perhaps a reference to blk_register_queue()? If so, please
mention the name of that function explicitly.
> + if (!q->debugfs_dir) {
> + q->debugfs_dir =
> + debugfs_create_dir(buts->name,
> + blk_debugfs_root);
> + }
> + dir = q->debugfs_dir;
> + }
> +
> + /*
> + * As blktrace relies on debugfs for its interface the debugfs directory
> + * is required, contrary to the usual mantra of not checking for debugfs
> + * files or directories.
> + */
> + if (IS_ERR_OR_NULL(q->debugfs_dir)) {
> + pr_warn("debugfs_dir not present for %s so skipping\n",
> + buts->name);
> + return -ENOENT;
> + }
How are do_blk_trace_setup() calls serialized against the debugfs directory
creation code in blk_register_queue()? Perhaps via q->blk_trace_mutex? Are
mutex lock and unlock calls for that mutex perhaps missing from
compat_blk_trace_setup()?
How about adding a lockdep_assert_held(&q->blk_trace_mutex) statement in
do_blk_trace_setup()?
Thanks,
Bart.
next prev parent reply other threads:[~2020-05-28 1:15 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-16 3:19 [PATCH v5 0/7] block: fix blktrace debugfs use after free Luis Chamberlain
2020-05-16 3:19 ` [PATCH v5 1/7] block: add docs for gendisk / request_queue refcount helpers Luis Chamberlain
2020-05-16 3:19 ` [PATCH v5 2/7] block: clarify context for gendisk / request_queue refcount increment helpers Luis Chamberlain
2020-05-16 3:19 ` [PATCH v5 3/7] block: revert back to synchronous request_queue removal Luis Chamberlain
2020-05-16 3:19 ` [PATCH v5 4/7] block: move main block debugfs initialization to its own file Luis Chamberlain
2020-05-19 15:33 ` Christoph Hellwig
2020-05-16 3:19 ` [PATCH v5 5/7] blktrace: fix debugfs use after free Luis Chamberlain
2020-05-19 14:44 ` Greg KH
2020-05-19 15:52 ` Luis Chamberlain
2020-05-19 17:03 ` Greg KH
2020-05-19 16:37 ` Christoph Hellwig
2020-05-19 16:54 ` Greg KH
2020-05-27 3:12 ` Luis Chamberlain
2020-05-28 1:15 ` Bart Van Assche [this message]
2020-05-29 7:56 ` Luis Chamberlain
2020-05-29 14:09 ` Bart Van Assche
2020-06-01 17:05 ` Luis Chamberlain
2020-06-05 4:48 ` Bart Van Assche
2020-06-05 22:33 ` Luis Chamberlain
2020-05-16 3:19 ` [PATCH v5 6/7] blktrace: break out of blktrace setup on concurrent calls Luis Chamberlain
2020-05-19 15:37 ` Christoph Hellwig
2020-05-19 16:10 ` Bart Van Assche
2020-05-16 3:19 ` [PATCH v5 7/7] loop: be paranoid on exit and prevent new additions / removals Luis Chamberlain
2020-05-19 15:36 ` Christoph Hellwig
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