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hamradio: defer 6pack kfree after unregister_netdev 

There is a possible race condition (use-after-free) like below

 (USE)                       |  (FREE)
  dev_queue_xmit             |
   __dev_queue_xmit          |
    __dev_xmit_skb           |
     sch_direct_xmit         | ...
      xmit_one               |
       netdev_start_xmit     | tty_ldisc_kill
        __netdev_start_xmit  |  6pack_close
         sp_xmit             |   kfree
          sp_encaps          |
                             |

According to the patch "defer ax25 kfree after unregister_netdev", this
patch reorder the kfree after the unregister_netdev to avoid the possible
UAF as the unregister_netdev() is well synchronized and won't return if
there is a running routine.

Signed-off-by: Lin Ma <linma@zju.edu.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Lin Ma 2021-11-08 18:37:59 +08:00 committed by David S. Miller
parent 3e0588c291
commit 0b9111922b
1 changed files with 4 additions and 2 deletions
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6
drivers/net/hamradio/6pack.c
View File

@ -672,11 +672,13 @@ static void sixpack_close(struct tty_struct *tty)
del_timer_sync(&sp->tx_t);
del_timer_sync(&sp->resync_t);
/* Free all 6pack frame buffers. */
unregister_netdev(sp->dev);
/* Free all 6pack frame buffers after unreg. */
kfree(sp->rbuff);
kfree(sp->xbuff);
unregister_netdev(sp->dev);
free_netdev(sp->dev);
}
/* Perform I/O control on an active 6pack channel. */