On Mon, Jun 05, 2023 at 01:57:30PM -0500, Mike Christie wrote:
If userspace does VHOST_VSOCK_SET_GUEST_CID before VHOST_SET_OWNER we
can race where:
1. thread0 calls vhost_transport_send_pkt -> vhost_work_queue
2. thread1 does VHOST_SET_OWNER which calls vhost_worker_create.
3. vhost_worker_create will set the dev->worker pointer before setting
the worker->vtsk pointer.
4. thread0's vhost_work_queue will see the dev->worker pointer is
set and try to call vhost_task_wake using not yet set worker->vtsk
pointer.
5. We then crash since vtsk is NULL.
Before commit 6e890c5d5021 ("vhost: use vhost_tasks for worker
threads"), we only had the worker pointer so we could just check it to
see if VHOST_SET_OWNER has been done. After that commit we have the
vhost_worker and vhost_task pointers, so we can now hit the bug above.
This patch embeds the vhost_worker in the vhost_dev, so we can just
check the worker.vtsk pointer to check if VHOST_SET_OWNER has been done
like before.
Fixes: 6e890c5d5021 ("vhost: use vhost_tasks for worker threads")
We should add:
Reported-by: syzbot+d0d442c22fa8db45f...@syzkaller.appspotmail.com
Signed-off-by: Mike Christie <michael.chris...@oracle.com>
---
drivers/vhost/vhost.c | 50 +++++++++++++++----------------------------
drivers/vhost/vhost.h | 2 +-
2 files changed, 18 insertions(+), 34 deletions(-)
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 074273020849..0ad9fea7c170 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -235,7 +235,7 @@ void vhost_dev_flush(struct vhost_dev *dev)
{
struct vhost_flush_struct flush;
- if (dev->worker) {
+ if (dev->worker.vtsk) {
init_completion(&flush.wait_event);
vhost_work_init(&flush.work, vhost_flush_work);
@@ -247,7 +247,7 @@ EXPORT_SYMBOL_GPL(vhost_dev_flush);
void vhost_work_queue(struct vhost_dev *dev, struct vhost_work *work)
{
- if (!dev->worker)
+ if (!dev->worker.vtsk)
return;
if (!test_and_set_bit(VHOST_WORK_QUEUED, &work->flags)) {
@@ -255,8 +255,8 @@ void vhost_work_queue(struct vhost_dev *dev, struct
vhost_work *work)
* sure it was not in the list.
* test_and_set_bit() implies a memory barrier.
*/
- llist_add(&work->node, &dev->worker->work_list);
- vhost_task_wake(dev->worker->vtsk);
+ llist_add(&work->node, &dev->worker.work_list);
+ vhost_task_wake(dev->worker.vtsk);
}
}
EXPORT_SYMBOL_GPL(vhost_work_queue);
@@ -264,7 +264,7 @@ EXPORT_SYMBOL_GPL(vhost_work_queue);
/* A lockless hint for busy polling code to exit the loop */
bool vhost_has_work(struct vhost_dev *dev)
{
- return dev->worker && !llist_empty(&dev->worker->work_list);
+ return !llist_empty(&dev->worker.work_list);
}
EXPORT_SYMBOL_GPL(vhost_has_work);
@@ -456,7 +456,7 @@ void vhost_dev_init(struct vhost_dev *dev,
dev->umem = NULL;
dev->iotlb = NULL;
dev->mm = NULL;
- dev->worker = NULL;
+ memset(&dev->worker, 0, sizeof(dev->worker));
dev->iov_limit = iov_limit;
dev->weight = weight;
dev->byte_weight = byte_weight;
@@ -530,47 +530,31 @@ static void vhost_detach_mm(struct vhost_dev *dev)
static void vhost_worker_free(struct vhost_dev *dev)
{
- struct vhost_worker *worker = dev->worker;
-
- if (!worker)
+ if (!dev->worker.vtsk)
return;
- dev->worker = NULL;
- WARN_ON(!llist_empty(&worker->work_list));
- vhost_task_stop(worker->vtsk);
- kfree(worker);
+ WARN_ON(!llist_empty(&dev->worker.work_list));
+ vhost_task_stop(dev->worker.vtsk);
+ dev->worker.kcov_handle = 0;
+ dev->worker.vtsk = NULL;
}
static int vhost_worker_create(struct vhost_dev *dev)
{
- struct vhost_worker *worker;
struct vhost_task *vtsk;
char name[TASK_COMM_LEN];
- int ret;
-
- worker = kzalloc(sizeof(*worker), GFP_KERNEL_ACCOUNT);
- if (!worker)
- return -ENOMEM;
- dev->worker = worker;
- worker->kcov_handle = kcov_common_handle();
- init_llist_head(&worker->work_list);
+ init_llist_head(&dev->worker.work_list);
snprintf(name, sizeof(name), "vhost-%d", current->pid);
- vtsk = vhost_task_create(vhost_worker, worker, name);
- if (!vtsk) {
- ret = -ENOMEM;
- goto free_worker;
- }
+ vtsk = vhost_task_create(vhost_worker, &dev->worker, name);
+ if (!vtsk)
+ return -ENOMEM;
- worker->vtsk = vtsk;
+ dev->worker.kcov_handle = kcov_common_handle();
+ dev->worker.vtsk = vtsk;
vhost_work_queue() is called by vhost_transport_send_pkt() without
holding vhost_dev.mutex (like vhost_poll_queue() in several places).
If vhost_work_queue() finds dev->worker.vtsk not NULL, how can we
be sure that for example `work_list` has been initialized?
Maybe I'm overthinking since we didn't have this problem before or the
race is really short that it never happened.
Thanks,
Stefano
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