From: Yu Kuai <yukuai1@huaweicloud.com> To: Christoph Hellwig <hch@lst.de>, Yu Kuai <yukuai1@huaweicloud.com> Cc: Jens Axboe <axboe@kernel.dk>, Alasdair Kergon <agk@redhat.com>, Mike Snitzer <snitzer@kernel.org>, dm-devel@redhat.com, linux-block@vger.kernel.org, "yukuai (C)" <yukuai3@huawei.com> Subject: Re: [PATCH 7/7] block: store the holder kobject in bd_holder_disk Date: Tue, 1 Nov 2022 19:28:17 +0800 [thread overview] Message-ID: <57465370-99fe-d8a5-e150-a1057640e972@huaweicloud.com> (raw) In-Reply-To: <20221101112131.GA14379@lst.de> Hi, 在 2022/11/01 19:21, Christoph Hellwig 写道: > On Tue, Nov 01, 2022 at 07:12:51PM +0800, Yu Kuai wrote: >>> But how could the reference be 0 here? The driver that calls >>> bd_link_disk_holder must have the block device open and thus hold a >>> reference to it. >> >> Like I said before, the caller of bd_link_disk_holder() get bdev by >> blkdev_get_by_dev(), which do not grab reference of holder_dir, and >> grab disk reference can only prevent disk_release() to be called, not >> del_gendisk() while holder_dir reference is dropped in del_gendisk() >> and can be decreased to 0. > > Oh, the bd_holder_dir reference, not the block_device one. So yes, > I agree. > >> If you agree with above explanation, I tried to fix this: >> >> 1) move kobject_put(bd_holder_dir) from del_gendisk to disk_release, >> there seems to be a lot of other dependencies. >> >> 2) protect bd_holder_dir reference by open_mutex. > > I think simply switching the kobject_get in bd_link_disk_holder > into a kobject_get_unless_zero and unwinding if there is no reference > should be enough: > > diff --git a/block/holder.c b/block/holder.c > index a8c355b9d0806..cd18064f6ff80 100644 > --- a/block/holder.c > +++ b/block/holder.c > @@ -83,7 +83,11 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk) > > INIT_LIST_HEAD(&holder->list); > holder->refcnt = 1; > - holder->holder_dir = kobject_get(bdev->bd_holder_dir); > + if (!kobject_get_unless_zero(bdev->bd_holder_dir)) { > + ret = -EBUSY; > + goto out_free_holder; > + } > + holder->holder_dir = bdev->bd_holder_dir; What if bd_holder_dir is already freed here, then uaf can be triggered. Thus bd_holder_dir need to be resed in del_gendisk() if it's reference is dropped to 0, however, kobject apis can't do that... Thanks, Kuai > > ret = add_symlink(disk->slave_dir, bdev_kobj(bdev)); > if (ret) > @@ -100,6 +104,7 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk) > del_symlink(disk->slave_dir, bdev_kobj(bdev)); > out_put_holder_dir: > kobject_put(holder->holder_dir); > +out_free_holder: > kfree(holder); > out_unlock: > mutex_unlock(&disk->open_mutex); > > . >
WARNING: multiple messages have this Message-ID (diff)
From: Yu Kuai <yukuai1@huaweicloud.com> To: Christoph Hellwig <hch@lst.de>, Yu Kuai <yukuai1@huaweicloud.com> Cc: Jens Axboe <axboe@kernel.dk>, Mike Snitzer <snitzer@kernel.org>, linux-block@vger.kernel.org, dm-devel@redhat.com, "yukuai \(C\)" <yukuai3@huawei.com>, Alasdair Kergon <agk@redhat.com> Subject: Re: [dm-devel] [PATCH 7/7] block: store the holder kobject in bd_holder_disk Date: Tue, 1 Nov 2022 19:28:17 +0800 [thread overview] Message-ID: <57465370-99fe-d8a5-e150-a1057640e972@huaweicloud.com> (raw) In-Reply-To: <20221101112131.GA14379@lst.de> Hi, 在 2022/11/01 19:21, Christoph Hellwig 写道: > On Tue, Nov 01, 2022 at 07:12:51PM +0800, Yu Kuai wrote: >>> But how could the reference be 0 here? The driver that calls >>> bd_link_disk_holder must have the block device open and thus hold a >>> reference to it. >> >> Like I said before, the caller of bd_link_disk_holder() get bdev by >> blkdev_get_by_dev(), which do not grab reference of holder_dir, and >> grab disk reference can only prevent disk_release() to be called, not >> del_gendisk() while holder_dir reference is dropped in del_gendisk() >> and can be decreased to 0. > > Oh, the bd_holder_dir reference, not the block_device one. So yes, > I agree. > >> If you agree with above explanation, I tried to fix this: >> >> 1) move kobject_put(bd_holder_dir) from del_gendisk to disk_release, >> there seems to be a lot of other dependencies. >> >> 2) protect bd_holder_dir reference by open_mutex. > > I think simply switching the kobject_get in bd_link_disk_holder > into a kobject_get_unless_zero and unwinding if there is no reference > should be enough: > > diff --git a/block/holder.c b/block/holder.c > index a8c355b9d0806..cd18064f6ff80 100644 > --- a/block/holder.c > +++ b/block/holder.c > @@ -83,7 +83,11 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk) > > INIT_LIST_HEAD(&holder->list); > holder->refcnt = 1; > - holder->holder_dir = kobject_get(bdev->bd_holder_dir); > + if (!kobject_get_unless_zero(bdev->bd_holder_dir)) { > + ret = -EBUSY; > + goto out_free_holder; > + } > + holder->holder_dir = bdev->bd_holder_dir; What if bd_holder_dir is already freed here, then uaf can be triggered. Thus bd_holder_dir need to be resed in del_gendisk() if it's reference is dropped to 0, however, kobject apis can't do that... Thanks, Kuai > > ret = add_symlink(disk->slave_dir, bdev_kobj(bdev)); > if (ret) > @@ -100,6 +104,7 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk) > del_symlink(disk->slave_dir, bdev_kobj(bdev)); > out_put_holder_dir: > kobject_put(holder->holder_dir); > +out_free_holder: > kfree(holder); > out_unlock: > mutex_unlock(&disk->open_mutex); > > . > -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel
next prev parent reply other threads:[~2022-11-01 11:29 UTC|newest] Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-10-30 15:31 fix delayed holder tracking v2 Christoph Hellwig 2022-10-30 15:31 ` [dm-devel] " Christoph Hellwig 2022-10-30 15:31 ` [PATCH 1/7] block: clear ->slave_dir when dropping the main slave_dir reference Christoph Hellwig 2022-10-30 15:31 ` [dm-devel] " Christoph Hellwig 2022-10-30 15:31 ` [PATCH 2/7] dm: remove free_table_devices Christoph Hellwig 2022-10-30 15:31 ` [dm-devel] " Christoph Hellwig 2022-10-30 15:31 ` [PATCH 3/7] dm: cleanup open_table_device Christoph Hellwig 2022-10-30 15:31 ` [dm-devel] " Christoph Hellwig 2022-10-30 15:31 ` [PATCH 4/7] dm: cleanup close_table_device Christoph Hellwig 2022-10-30 15:31 ` [dm-devel] " Christoph Hellwig 2022-10-30 15:31 ` [PATCH 5/7] dm: track per-add_disk holder relations in DM Christoph Hellwig 2022-10-30 15:31 ` [dm-devel] " Christoph Hellwig 2022-11-09 2:08 ` Yu Kuai 2022-11-09 2:08 ` [dm-devel] " Yu Kuai 2022-11-09 8:26 ` Christoph Hellwig 2022-11-09 8:26 ` [dm-devel] " Christoph Hellwig 2022-11-10 18:09 ` Mike Snitzer 2022-11-10 18:09 ` [dm-devel] " Mike Snitzer 2022-11-10 19:48 ` Mike Snitzer 2022-11-10 19:48 ` Mike Snitzer 2022-11-12 6:23 ` Yu Kuai 2022-11-12 6:23 ` [dm-devel] " Yu Kuai 2022-10-30 15:31 ` [PATCH 6/7] block: remove delayed holder registration Christoph Hellwig 2022-10-30 15:31 ` [dm-devel] " Christoph Hellwig 2022-10-30 15:31 ` [PATCH 7/7] block: store the holder kobject in bd_holder_disk Christoph Hellwig 2022-10-30 15:31 ` [dm-devel] " Christoph Hellwig 2022-10-31 1:52 ` Yu Kuai 2022-10-31 1:52 ` [dm-devel] " Yu Kuai 2022-11-01 10:49 ` Christoph Hellwig 2022-11-01 10:49 ` [dm-devel] " Christoph Hellwig 2022-11-01 11:12 ` Yu Kuai 2022-11-01 11:12 ` [dm-devel] " Yu Kuai 2022-11-01 11:21 ` Christoph Hellwig 2022-11-01 11:21 ` [dm-devel] " Christoph Hellwig 2022-11-01 11:28 ` Yu Kuai [this message] 2022-11-01 11:28 ` Yu Kuai 2022-11-01 13:18 ` Christoph Hellwig 2022-11-01 13:18 ` [dm-devel] " Christoph Hellwig 2022-11-01 13:29 ` Yu Kuai 2022-11-01 13:29 ` [dm-devel] " Yu Kuai
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