From: Jan Kara <jack@suse.cz>
To: Yufen Yu <yuyufen@huawei.com>
Cc: Christoph Hellwig <hch@lst.de>,
axboe@kernel.dk, tj@kernel.org, jack@suse.cz, bvanassche@acm.org,
tytso@mit.edu, gregkh@linuxfoundation.org,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/8] bdi: add a ->dev_name field to struct backing_dev_info
Date: Thu, 16 Apr 2020 14:02:23 +0200 [thread overview]
Message-ID: <20200416120223.GI23739@quack2.suse.cz> (raw)
In-Reply-To: <5bfcd35a-2463-3769-be93-911c4e3c38bb@huawei.com>
On Thu 16-04-20 16:34:13, Yufen Yu wrote:
> Hi,
>
> On 2020/4/16 15:15, Christoph Hellwig wrote:
> > Cache a copy of the name for the life time of the backing_dev_info
> > structure so that we can reference it even after unregistering.
> >
> > Fixes: 68f23b89067f ("memcg: fix a crash in wb_workfn when a device disappears")
> > Reported-by: Yufen Yu <yuyufen@huawei.com>
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > ---
> > include/linux/backing-dev-defs.h | 1 +
> > mm/backing-dev.c | 13 ++++++++++---
> > 2 files changed, 11 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
> > index 4fc87dee005a..249590bcccf7 100644
> > --- a/include/linux/backing-dev-defs.h
> > +++ b/include/linux/backing-dev-defs.h
> > @@ -220,6 +220,7 @@ struct backing_dev_info {
> > wait_queue_head_t wb_waitq;
> > struct device *dev;
> > + const char *dev_name;
> > struct device *owner;
> > struct timer_list laptop_mode_wb_timer;
> > diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> > index c2c44c89ee5d..4f6c05df72f9 100644
> > --- a/mm/backing-dev.c
> > +++ b/mm/backing-dev.c
> > @@ -938,9 +938,15 @@ int bdi_register_va(struct backing_dev_info *bdi, const char *fmt, va_list args)
> > if (bdi->dev) /* The driver needs to use separate queues per device */
> > return 0;
> > - dev = device_create_vargs(bdi_class, NULL, MKDEV(0, 0), bdi, fmt, args);
> > - if (IS_ERR(dev))
> > + bdi->dev_name = kvasprintf(GFP_KERNEL, fmt, args);
> > + if (!bdi->dev_name)
> > + return -ENOMEM;
> > +
> > + dev = device_create(bdi_class, NULL, MKDEV(0, 0), bdi, bdi->dev_name);
> > + if (IS_ERR(dev)) {
> > + kfree(bdi->dev_name);
> > return PTR_ERR(dev);
> > + }
> > cgwb_bdi_register(bdi);
> > bdi->dev = dev;
> > @@ -1034,6 +1040,7 @@ static void release_bdi(struct kref *ref)
> > WARN_ON_ONCE(bdi->dev);
> > wb_exit(&bdi->wb);
> > cgwb_bdi_exit(bdi);
> > + kfree(bdi->dev_name);
> > kfree(bdi);
> > }
>
>
> When driver try to to re-register bdi but without release_bdi(), the old
> dev_name will be cover directly by the newer in bdi_register_va(). So, I
> am not sure whether it can cause memory leak for bdi->dev_name.
Yes, that can indeed happen. E.g. I remember that drivers/scsi/sd.c calls
device_add_disk() + del_gendisk() repeatedly for one request_queue and that
would result in leaking the name (and possibly cause use-after-free
issues). I think dev_name has to be just a static array inside
backing_dev_info which gets overwritten on reregistration. The question is
how big should be this array... Some grepping shows that 40 bytes should be
enough for everybody except fs/vboxsf/super.c which puts 'fc->source' into
the name which can be presumably rather large. Anyway, I'd make it 40 and
just truncate it case in case it does not fit. bdi_dev_name() is used for
informational purposes anyway...
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2020-04-16 12:02 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-16 7:15 bdi: fix use-after-free for dev_name(bdi->dev) Christoph Hellwig
2020-04-16 7:15 ` [PATCH 1/8] bdi: move bdi_dev_name out of line Christoph Hellwig
2020-04-16 7:52 ` Greg KH
2020-04-16 12:32 ` Jan Kara
2020-04-16 7:15 ` [PATCH 2/8] bdi: use bdi_dev_name() to get device name Christoph Hellwig
2020-04-16 7:52 ` Greg KH
2020-04-16 7:15 ` [PATCH 3/8] bdi: add a ->dev_name field to struct backing_dev_info Christoph Hellwig
2020-04-16 7:52 ` Greg KH
2020-04-16 8:34 ` Yufen Yu
2020-04-16 12:02 ` Jan Kara [this message]
2020-04-16 12:19 ` Christoph Hellwig
2020-04-16 12:22 ` Christoph Hellwig
2020-04-16 12:31 ` Jan Kara
2020-04-16 7:15 ` [PATCH 4/8] driver core: remove device_create_vargs Christoph Hellwig
2020-04-16 7:52 ` Greg KH
2020-04-16 7:15 ` [PATCH 5/8] bdi: unexport bdi_register_va Christoph Hellwig
2020-04-16 7:53 ` Greg KH
2020-04-16 12:03 ` Jan Kara
2020-04-16 7:15 ` [PATCH 6/8] bdi: remove bdi_register_owner Christoph Hellwig
2020-04-16 7:53 ` Greg KH
2020-04-16 12:05 ` Jan Kara
2020-04-16 7:15 ` [PATCH 7/8] bdi: simplify bdi_alloc Christoph Hellwig
2020-04-16 7:54 ` Greg KH
2020-04-16 12:06 ` Jan Kara
2020-04-16 7:15 ` [PATCH 8/8] bdi: remove the name field in struct backing_dev_info Christoph Hellwig
2020-04-16 7:54 ` Greg KH
2020-04-16 12:23 ` Jan Kara
2020-04-16 15:29 ` bdi: fix use-after-free for dev_name(bdi->dev) Jens Axboe
2020-04-16 15:29 ` Christoph Hellwig
2020-04-16 15:30 ` Jens Axboe
2020-04-16 16:54 bdi: fix use-after-free for dev_name(bdi->dev) v2 Christoph Hellwig
2020-04-16 16:54 ` [PATCH 3/8] bdi: add a ->dev_name field to struct backing_dev_info Christoph Hellwig
2020-04-17 8:59 ` Jan Kara
2020-04-17 13:01 ` Christoph Hellwig
2020-04-20 11:41 ` Hans de Goede
2020-04-20 11:58 ` Christoph Hellwig
2020-04-21 12:42 ` Hans de Goede
2020-04-18 15:40 ` Bart Van Assche
2020-04-19 7:58 ` Christoph Hellwig
2020-04-19 15:29 ` Bart Van Assche
2020-04-19 16:06 ` Christoph Hellwig
2020-04-20 7:48 ` Christoph Hellwig
2020-04-20 9:52 ` Jan Kara
2020-04-20 9:49 ` Jan Kara
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