From 4678d6f970c2f7c0cbfefc0cc666432d153b321b Mon Sep 17 00:00:00 2001 From: "Michael S. Tsirkin" Date: Thu, 12 Jan 2012 15:44:44 +1030 Subject: [PATCH] virtio_blk: fix config handler race Fix a theoretical race related to config work handler: a config interrupt might happen after we flush config work but before we reset the device. It will then cause the config work to run during or after reset. Two problems with this: - if this runs after device is gone we will get use after free - access of config while reset is in progress is racy (as layout is changing). As a solution 1. flush after reset when we know there will be no more interrupts 2. add a flag to disable config access before reset Signed-off-by: Michael S. Tsirkin Signed-off-by: Rusty Russell --- drivers/block/virtio_blk.c | 22 +++++++++++++++++++++- 1 file changed, 21 insertions(+), 1 deletion(-) diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c index a345e40e1bca..ba73661fb9f3 100644 --- a/drivers/block/virtio_blk.c +++ b/drivers/block/virtio_blk.c @@ -4,6 +4,7 @@ #include #include #include +#include #include #include #include @@ -36,6 +37,12 @@ struct virtio_blk /* Process context for config space updates */ struct work_struct config_work; + /* Lock for config space updates */ + struct mutex config_lock; + + /* enable config space updates */ + bool config_enable; + /* What host tells us, plus 2 for header & tailer. */ unsigned int sg_elems; @@ -318,6 +325,10 @@ static void virtblk_config_changed_work(struct work_struct *work) char cap_str_2[10], cap_str_10[10]; u64 capacity, size; + mutex_lock(&vblk->config_lock); + if (!vblk->config_enable) + goto done; + /* Host must always specify the capacity. */ vdev->config->get(vdev, offsetof(struct virtio_blk_config, capacity), &capacity, sizeof(capacity)); @@ -340,6 +351,8 @@ static void virtblk_config_changed_work(struct work_struct *work) cap_str_10, cap_str_2); set_capacity(vblk->disk, capacity); +done: + mutex_unlock(&vblk->config_lock); } static void virtblk_config_changed(struct virtio_device *vdev) @@ -388,7 +401,9 @@ static int __devinit virtblk_probe(struct virtio_device *vdev) vblk->vdev = vdev; vblk->sg_elems = sg_elems; sg_init_table(vblk->sg, vblk->sg_elems); + mutex_init(&vblk->config_lock); INIT_WORK(&vblk->config_work, virtblk_config_changed_work); + vblk->config_enable = true; /* We expect one virtqueue, for output. */ vblk->vq = virtio_find_single_vq(vdev, blk_done, "requests"); @@ -542,7 +557,10 @@ static void __devexit virtblk_remove(struct virtio_device *vdev) struct virtio_blk *vblk = vdev->priv; int index = vblk->index; - flush_work(&vblk->config_work); + /* Prevent config work handler from accessing the device. */ + mutex_lock(&vblk->config_lock); + vblk->config_enable = false; + mutex_unlock(&vblk->config_lock); /* Nothing should be pending. */ BUG_ON(!list_empty(&vblk->reqs)); @@ -550,6 +568,8 @@ static void __devexit virtblk_remove(struct virtio_device *vdev) /* Stop all the virtqueues. */ vdev->config->reset(vdev); + flush_work(&vblk->config_work); + del_gendisk(vblk->disk); blk_cleanup_queue(vblk->disk->queue); put_disk(vblk->disk); -- 2.20.1