Re: [PATCH -next] nbd: get config_lock before sock_shutdown

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在 2023/07/07 14:22, Zhong Jinghua 写道:
Config->socks in sock_shutdown may trigger a UAF problem.
The reason is that sock_shutdown does not hold the config_lock,
so that nbd_ioctl can release config->socks at this time.

T0: NBD_SET_SOCK
T1: NBD_DO_IT

T0						T1

nbd_ioctl
   mutex_lock(&nbd->config_lock)
   // get lock
   __nbd_ioctl
     nbd_start_device_ioctl
       nbd_start_device
        mutex_unlock(&nbd->config_lock)
          // relase lock
          wait_event_interruptible
          (kill, enter sock_shutdown)
          sock_shutdown
					nbd_ioctl
					  mutex_lock(&nbd->config_lock)
					  // get lock
					  __nbd_ioctl
					    nbd_add_socket
					      krealloc
						kfree(p)
					        //config->socks is NULL
            nbd_sock *nsock = config->socks // error

Fix it by moving config_lock up before sock_shutdown.

LGTM
Reviewed-by: Yu Kuai <yukuai3@xxxxxxxxxx>


Signed-off-by: Zhong Jinghua <zhongjinghua@xxxxxxxxxxxxxxx>
---
  drivers/block/nbd.c | 7 ++++++-
  1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index c410cf29fb0c..accbe99ebb7e 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -1428,13 +1428,18 @@ static int nbd_start_device_ioctl(struct nbd_device *nbd)
  	mutex_unlock(&nbd->config_lock);
  	ret = wait_event_interruptible(config->recv_wq,
  					 atomic_read(&config->recv_threads) == 0);
+
+	/*
+	 * recv_work in flush_workqueue will not get this lock, because nbd_open
+	 * will hold nbd->config_refs
+	 */
+	mutex_lock(&nbd->config_lock);
  	if (ret) {
  		sock_shutdown(nbd);
  		nbd_clear_que(nbd);
  	}
flush_workqueue(nbd->recv_workq);
-	mutex_lock(&nbd->config_lock);
  	nbd_bdev_reset(nbd);
  	/* user requested, ignore socket errors */
  	if (test_bit(NBD_RT_DISCONNECT_REQUESTED, &config->runtime_flags))





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