hamradio: remove needs_free_netdev to avoid UAF

The former patch "defer 6pack kfree after unregister_netdev" reorders
the kfree of two buffer after the unregister_netdev to prevent the race
condition. It also adds free_netdev() function in sixpack_close(), which
is a direct copy from the similar code in mkiss_close().

However, in sixpack driver, the flag needs_free_netdev is set to true in
sp_setup(), hence the unregister_netdev() will free the netdev
automatically. Therefore, as the sp is netdev_priv, use-after-free
occurs.

This patch removes the needs_free_netdev = true and just let the
free_netdev to finish this deallocation task.

Fixes: 0b9111922b1f ("hamradio: defer 6pack kfree after unregister_netdev")
Signed-off-by: Lin Ma <linma@zju.edu.cn>
Link: https://lore.kernel.org/r/20211111141402.7551-1-linma@zju.edu.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/hamradio/6pack.c b/drivers/net/hamradio/6pack.c
index bfdf89e54752c59b5b43f26ecccfac66f47cf907..8a19a06b505d125dcc88e7accd1765b4decb7530 100644 (file)
--- a/drivers/net/hamradio/6pack.c
+++ b/drivers/net/hamradio/6pack.c
@@ -306,7 +306,6 @@ static void sp_setup(struct net_device *dev)
 {
        /* Finish setting up the DEVICE info. */
        dev->netdev_ops         = &sp_netdev_ops;
-       dev->needs_free_netdev  = true;
        dev->mtu                = SIXP_MTU;
        dev->hard_header_len    = AX25_MAX_HEADER_LEN;
        dev->header_ops         = &ax25_header_ops;