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From: Luis Chamberlain <mcgrof@kernel.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: Jan Kara <jack@suse.cz>,
	axboe@kernel.dk, viro@zeniv.linux.org.uk, bvanassche@acm.org,
	gregkh@linuxfoundation.org, rostedt@goodmis.org,
	mingo@redhat.com, ming.lei@redhat.com, nstange@suse.de,
	akpm@linux-foundation.org, mhocko@suse.com, yukuai3@huawei.com,
	martin.petersen@oracle.com, jejb@linux.ibm.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 v6 6/6] blktrace: fix debugfs use after free
Date: Tue, 9 Jun 2020 17:53:59 +0000	[thread overview]
Message-ID: <20200609175359.GR11244@42.do-not-panic.com> (raw)
In-Reply-To: <20200609173218.GA7968@infradead.org>

On Tue, Jun 09, 2020 at 10:32:18AM -0700, Christoph Hellwig wrote:
> On Tue, Jun 09, 2020 at 05:29:22PM +0000, Luis Chamberlain wrote:
> > Is scsi-generic is the only unwanted ugly child blktrace has to deal
> > with? For some reason I thought drivers/md/md.c was one but it seems
> > like it is not. Do we have an easy way to search for these? I think
> > this would just affect how we express the comment only.
> 
> grep for blk_trace_setup.  For all blk devices that setup comes in
> through the block device ioctl path, and that relies on having a
> struct block_device and queue.  sg on the other hand calls
> blk_trace_setup directly with a NULL bdev argument.

Alright, then we should be good.

> > >  		 */
> > > -		dir = q->sg_debugfs_dir;
> > > +		dir = debugfs_create_dir(buts->name, blk_debugfs_root);
> > > +		bt->dir = dir;
> > 
> > The other chicken and egg problem to consider at least in the comments
> > is that the debugfs directory for these types of devices *have* an
> > exposed path, but the data structure is rather opaque to the device and
> > even blktrace.  Fortunately given the recent set of changes around the
> > q->blk_trace and clarifications around its use we have made it clear now
> > that so long as hold the q->blk_trace_mutex *and* check q->blk_trace we
> > *should* not race against two separate creations of debugfs directories,
> > so I think this is safe, so long as these indpendent drivers don't end
> > up re-using the same path for some other things later in the future, and
> > since we have control over what goes under debugfsroot block / I think
> > we should be good.
> > 
> > But I think that the concern for race on names may still be worth
> > explaining a bit here.
> 
> Feel free to add more comments, but please try to keep them short
> and crisp.  At the some point long comments really distract from what
> is going on.

Sure.

Come to think of it, given the above, I think we can also do way with
the the partition stuff too, and rely on the buts->name too. I'll try
this out, and test it.

  Luis

  reply	other threads:[~2020-06-09 17:54 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-08 17:01 [PATCH v6 0/8] block: fix blktrace " Luis Chamberlain
2020-06-08 17:01 ` [PATCH v6 1/6] block: add docs for gendisk / request_queue refcount helpers Luis Chamberlain
2020-06-08 17:01 ` [PATCH v6 2/6] block: clarify context for refcount increment helpers Luis Chamberlain
2020-06-08 17:01 ` [PATCH v6 3/6] block: revert back to synchronous request_queue removal Luis Chamberlain
2020-06-13  1:53   ` Bart Van Assche
2020-06-19 20:23     ` Luis Chamberlain
2020-06-08 17:01 ` [PATCH v6 4/6] blktrace: annotate required lock on do_blk_trace_setup() Luis Chamberlain
2020-06-09 14:18   ` Christoph Hellwig
2020-06-13  1:54   ` Bart Van Assche
2020-06-08 17:01 ` [PATCH v6 5/6] loop: be paranoid on exit and prevent new additions / removals Luis Chamberlain
2020-06-08 17:01 ` [PATCH v6 6/6] blktrace: fix debugfs use after free Luis Chamberlain
2020-06-09 15:06   ` Christoph Hellwig
2020-06-09 17:29     ` Luis Chamberlain
2020-06-09 17:32       ` Christoph Hellwig
2020-06-09 17:53         ` Luis Chamberlain [this message]
2020-06-10  6:42           ` Christoph Hellwig
2020-06-10 21:09             ` Luis Chamberlain
2020-06-10 21:52               ` Luis Chamberlain
2020-06-10 23:31                 ` Luis Chamberlain
2020-06-11  5:40                   ` Christoph Hellwig
2020-06-13  2:42   ` Bart Van Assche
2020-06-19 15:36     ` Luis Chamberlain

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