Re: [PATCH 1/2] vhost-vdpa: fix use-after-free of v->config_ctx

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On 2021/3/11 9:52 下午, Stefano Garzarella wrote:
When the 'v->config_ctx' eventfd_ctx reference is released we didn't
set it to NULL. So if the same character device (e.g. /dev/vhost-vdpa-0)
is re-opened, the 'v->config_ctx' is invalid and calling again
vhost_vdpa_config_put() causes use-after-free issues like the
following refcount_t underflow:

     refcount_t: underflow; use-after-free.
     WARNING: CPU: 2 PID: 872 at lib/refcount.c:28 refcount_warn_saturate+0xae/0xf0
     RIP: 0010:refcount_warn_saturate+0xae/0xf0
     Call Trace:
      eventfd_ctx_put+0x5b/0x70
      vhost_vdpa_release+0xcd/0x150 [vhost_vdpa]
      __fput+0x8e/0x240
      ____fput+0xe/0x10
      task_work_run+0x66/0xa0
      exit_to_user_mode_prepare+0x118/0x120
      syscall_exit_to_user_mode+0x21/0x50
      ? __x64_sys_close+0x12/0x40
      do_syscall_64+0x45/0x50
      entry_SYSCALL_64_after_hwframe+0x44/0xae

Fixes: 776f395004d8 ("vhost_vdpa: Support config interrupt in vdpa")
Cc: lingshan.zhu@xxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>


Acked-by: Jason Wang <jasowang@xxxxxxxxxx>


---
  drivers/vhost/vdpa.c | 4 +++-
  1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
index ef688c8c0e0e..00796e4ecfdf 100644
--- a/drivers/vhost/vdpa.c
+++ b/drivers/vhost/vdpa.c
@@ -308,8 +308,10 @@ static long vhost_vdpa_get_vring_num(struct vhost_vdpa *v, u16 __user *argp)
static void vhost_vdpa_config_put(struct vhost_vdpa *v)
  {
-	if (v->config_ctx)
+	if (v->config_ctx) {
  		eventfd_ctx_put(v->config_ctx);
+		v->config_ctx = NULL;
+	}
  }
static long vhost_vdpa_set_config_call(struct vhost_vdpa *v, u32 __user *argp)




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