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[79.49.207.108]) by smtp.gmail.com with ESMTPSA id l4sm2984683wrv.60.2020.04.30.01.43.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Apr 2020 01:43:26 -0700 (PDT) Date: Thu, 30 Apr 2020 10:43:23 +0200 From: Stefano Garzarella To: Stefan Hajnoczi Cc: virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, "Michael S. Tsirkin" , Christoph Hellwig , linux-block@vger.kernel.org, Paolo Bonzini , Jens Axboe , cohuck@redhat.com, Jason Wang , Lance Digby Subject: Re: [PATCH v3] virtio-blk: handle block_device_operations callbacks after hot unplug Message-ID: <20200430084323.qts2q5ql7rkclk2h@steredhat> References: <20200429165345.144702-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200429165345.144702-1-stefanha@redhat.com> Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Wed, Apr 29, 2020 at 05:53:45PM +0100, Stefan Hajnoczi wrote: > A userspace process holding a file descriptor to a virtio_blk device can > still invoke block_device_operations after hot unplug. This leads to a > use-after-free accessing vblk->vdev in virtblk_getgeo() when > ioctl(HDIO_GETGEO) is invoked: > > BUG: unable to handle kernel NULL pointer dereference at 0000000000000090 > IP: [] virtio_check_driver_offered_feature+0x10/0x90 [virtio] > PGD 800000003a92f067 PUD 3a930067 PMD 0 > Oops: 0000 [#1] SMP > CPU: 0 PID: 1310 Comm: hdio-getgeo Tainted: G OE ------------ 3.10.0-1062.el7.x86_64 #1 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014 > task: ffff9be5fbfb8000 ti: ffff9be5fa890000 task.ti: ffff9be5fa890000 > RIP: 0010:[] [] virtio_check_driver_offered_feature+0x10/0x90 [virtio] > RSP: 0018:ffff9be5fa893dc8 EFLAGS: 00010246 > RAX: ffff9be5fc3f3400 RBX: ffff9be5fa893e30 RCX: 0000000000000000 > RDX: 0000000000000000 RSI: 0000000000000004 RDI: ffff9be5fbc10b40 > RBP: ffff9be5fa893dc8 R08: 0000000000000301 R09: 0000000000000301 > R10: 0000000000000000 R11: 0000000000000000 R12: ffff9be5fdc24680 > R13: ffff9be5fbc10b40 R14: ffff9be5fbc10480 R15: 0000000000000000 > FS: 00007f1bfb968740(0000) GS:ffff9be5ffc00000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000000000000090 CR3: 000000003a894000 CR4: 0000000000360ff0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > Call Trace: > [] virtblk_getgeo+0x47/0x110 [virtio_blk] > [] ? handle_mm_fault+0x39d/0x9b0 > [] blkdev_ioctl+0x1f5/0xa20 > [] block_ioctl+0x41/0x50 > [] do_vfs_ioctl+0x3a0/0x5a0 > [] SyS_ioctl+0xa1/0xc0 > > A related problem is that virtblk_remove() leaks the vd_index_ida index > when something still holds a reference to vblk->disk during hot unplug. > This causes virtio-blk device names to be lost (vda, vdb, etc). > > Fix these issues by protecting vblk->vdev with a mutex and reference > counting vblk so the vd_index_ida index can be removed in all cases. > > Fixes: 48e4043d4529523cbc7fa8dd745bd8e2c45ce1d3 > ("virtio: add virtio disk geometry feature") > Reported-by: Lance Digby > Signed-off-by: Stefan Hajnoczi > --- > drivers/block/virtio_blk.c | 87 ++++++++++++++++++++++++++++++++++---- > 1 file changed, 79 insertions(+), 8 deletions(-) > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c > index 93468b7c6701..6f7f277495f4 100644 > --- a/drivers/block/virtio_blk.c > +++ b/drivers/block/virtio_blk.c > @@ -33,6 +33,16 @@ struct virtio_blk_vq { > } ____cacheline_aligned_in_smp; > > struct virtio_blk { > + /* > + * vdev may be accessed without taking this mutex in blk-mq and > + * virtqueue code paths because virtblk_remove() stops them before vdev > + * is freed. > + * > + * Everything else must hold this mutex when accessing vdev and must > + * handle the case where vdev is NULL after virtblk_remove() has been > + * called. > + */ > + struct mutex vdev_mutex; The patch LGTM, I'm just worried about cache_type_store() and cache_type_show() because IIUC they aren't in blk-mq and virtqueue code paths, but they use vdev. Do we have to take the mutex there too? Thanks, Stefano > struct virtio_device *vdev; > > /* The disk structure for the kernel. */ > @@ -44,6 +54,13 @@ struct virtio_blk { > /* Process context for config space updates */ > struct work_struct config_work; > > + /* > + * Tracks references from block_device_operations open/release and > + * virtio_driver probe/remove so this object can be freed once no > + * longer in use. > + */ > + refcount_t refs; > + > /* What host tells us, plus 2 for header & tailer. */ > unsigned int sg_elems; > > @@ -295,10 +312,55 @@ static int virtblk_get_id(struct gendisk *disk, char *id_str) > return err; > } > > +static void virtblk_get(struct virtio_blk *vblk) > +{ > + refcount_inc(&vblk->refs); > +} > + > +static void virtblk_put(struct virtio_blk *vblk) > +{ > + if (refcount_dec_and_test(&vblk->refs)) { > + ida_simple_remove(&vd_index_ida, vblk->index); > + mutex_destroy(&vblk->vdev_mutex); > + kfree(vblk); > + } > +} > + > +static int virtblk_open(struct block_device *bd, fmode_t mode) > +{ > + struct virtio_blk *vblk = bd->bd_disk->private_data; > + int ret = 0; > + > + mutex_lock(&vblk->vdev_mutex); > + > + if (vblk->vdev) > + virtblk_get(vblk); > + else > + ret = -ENXIO; > + > + mutex_unlock(&vblk->vdev_mutex); > + return ret; > +} > + > +static void virtblk_release(struct gendisk *disk, fmode_t mode) > +{ > + struct virtio_blk *vblk = disk->private_data; > + > + virtblk_put(vblk); > +} > + > /* We provide getgeo only to please some old bootloader/partitioning tools */ > static int virtblk_getgeo(struct block_device *bd, struct hd_geometry *geo) > { > struct virtio_blk *vblk = bd->bd_disk->private_data; > + int ret = 0; > + > + mutex_lock(&vblk->vdev_mutex); > + > + if (!vblk->vdev) { > + ret = -ENXIO; > + goto out; > + } > > /* see if the host passed in geometry config */ > if (virtio_has_feature(vblk->vdev, VIRTIO_BLK_F_GEOMETRY)) { > @@ -314,11 +376,15 @@ static int virtblk_getgeo(struct block_device *bd, struct hd_geometry *geo) > geo->sectors = 1 << 5; > geo->cylinders = get_capacity(bd->bd_disk) >> 11; > } > - return 0; > +out: > + mutex_unlock(&vblk->vdev_mutex); > + return ret; > } > > static const struct block_device_operations virtblk_fops = { > .owner = THIS_MODULE, > + .open = virtblk_open, > + .release = virtblk_release, > .getgeo = virtblk_getgeo, > }; > > @@ -655,6 +721,10 @@ static int virtblk_probe(struct virtio_device *vdev) > goto out_free_index; > } > > + /* This reference is dropped in virtblk_remove(). */ > + refcount_set(&vblk->refs, 1); > + mutex_init(&vblk->vdev_mutex); > + > vblk->vdev = vdev; > vblk->sg_elems = sg_elems; > > @@ -820,8 +890,6 @@ static int virtblk_probe(struct virtio_device *vdev) > static void virtblk_remove(struct virtio_device *vdev) > { > struct virtio_blk *vblk = vdev->priv; > - int index = vblk->index; > - int refc; > > /* Make sure no work handler is accessing the device. */ > flush_work(&vblk->config_work); > @@ -831,18 +899,21 @@ static void virtblk_remove(struct virtio_device *vdev) > > blk_mq_free_tag_set(&vblk->tag_set); > > + mutex_lock(&vblk->vdev_mutex); > + > /* Stop all the virtqueues. */ > vdev->config->reset(vdev); > > - refc = kref_read(&disk_to_dev(vblk->disk)->kobj.kref); > + /* Virtqueues are stopped, nothing can use vblk->vdev anymore. */ > + vblk->vdev = NULL; > + > put_disk(vblk->disk); > vdev->config->del_vqs(vdev); > kfree(vblk->vqs); > - kfree(vblk); > > - /* Only free device id if we don't have any users */ > - if (refc == 1) > - ida_simple_remove(&vd_index_ida, index); > + mutex_unlock(&vblk->vdev_mutex); > + > + virtblk_put(vblk); > } > > #ifdef CONFIG_PM_SLEEP > -- > 2.25.3 >