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Tsirkin" , Lance Digby Subject: Re: [PATCH v4] virtio-blk: handle block_device_operations callbacks after hot unplug Message-ID: <20200504134834.423eb89e.cohuck@redhat.com> In-Reply-To: <20200430140442.171016-1-stefanha@redhat.com> References: <20200430140442.171016-1-stefanha@redhat.com> Organization: Red Hat GmbH MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Thu, 30 Apr 2020 15:04:42 +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") Should be Fixes: 48e4043d4529 ("virtio: add virtio disk geometry feature") > Reported-by: Lance Digby > Signed-off-by: Stefan Hajnoczi > --- > v4: > * Clarify vdev_mutex usage [Stefano and Michael] > > drivers/block/virtio_blk.c | 86 ++++++++++++++++++++++++++++++++++---- > 1 file changed, 78 insertions(+), 8 deletions(-) > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c > index 93468b7c6701..9d21bf0f155e 100644 > --- a/drivers/block/virtio_blk.c > +++ b/drivers/block/virtio_blk.c > @@ -33,6 +33,15 @@ struct virtio_blk_vq { > } ____cacheline_aligned_in_smp; > > struct virtio_blk { > + /* > + * This mutex must be held by anything that may run after > + * virtblk_remove() sets vblk->vdev to NULL. > + * > + * blk-mq, virtqueue processing, and sysfs attribute code paths are > + * shut down before vblk->vdev is set to NULL and therefore do not need > + * to hold this mutex. > + */ > + struct mutex vdev_mutex; > struct virtio_device *vdev; > > /* The disk structure for the kernel. */ > @@ -44,6 +53,13 @@ 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; Using a struct kref might be more idiomatic. > + > /* What host tells us, plus 2 for header & tailer. */ > unsigned int sg_elems; > > @@ -295,10 +311,55 @@ 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); Should the code even be able to grab a ref if !vblk->vdev? > +} > + > +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); I think that's where putting these cleanups into a release() funtion would be more idiomatic. > + } > +} (...) Looks sane to me.