提交 a87d6afa 编写于 作者: L Lin Ma 提交者: Zheng Zengkai

hamradio: improve the incomplete fix to avoid NPD

stable inclusion
from stable-v5.10.89
commit 7dd52af1eb5798f590d9d9e1c56ed8f5744ee0ca
bugzilla: 186140 https://gitee.com/openeuler/kernel/issues/I4S8HA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7dd52af1eb5798f590d9d9e1c56ed8f5744ee0ca

--------------------------------

commit b2f37aea upstream.

The previous commit 3e0588c2 ("hamradio: defer ax25 kfree after
unregister_netdev") reorder the kfree operations and unregister_netdev
operation to prevent UAF.

This commit improves the previous one by also deferring the nullify of
the ax->tty pointer. Otherwise, a NULL pointer dereference bug occurs.
Partial of the stack trace is shown below.

BUG: kernel NULL pointer dereference, address: 0000000000000538
RIP: 0010:ax_xmit+0x1f9/0x400
...
Call Trace:
 dev_hard_start_xmit+0xec/0x320
 sch_direct_xmit+0xea/0x240
 __qdisc_run+0x166/0x5c0
 __dev_queue_xmit+0x2c7/0xaf0
 ax25_std_establish_data_link+0x59/0x60
 ax25_connect+0x3a0/0x500
 ? security_socket_connect+0x2b/0x40
 __sys_connect+0x96/0xc0
 ? __hrtimer_init+0xc0/0xc0
 ? common_nsleep+0x2e/0x50
 ? switch_fpu_return+0x139/0x1a0
 __x64_sys_connect+0x11/0x20
 do_syscall_64+0x33/0x40
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

The crash point is shown as below

static void ax_encaps(...) {
  ...
  set_bit(TTY_DO_WRITE_WAKEUP, &ax->tty->flags); // ax->tty = NULL!
  ...
}

By placing the nullify action after the unregister_netdev, the ax->tty
pointer won't be assigned as NULL net_device framework layer is well
synchronized.
Signed-off-by: NLin Ma <linma@zju.edu.cn>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
上级 5005c502
无相关合并请求
......@@ -792,14 +792,14 @@ static void mkiss_close(struct tty_struct *tty)
*/
netif_stop_queue(ax->dev);
ax->tty = NULL;
unregister_netdev(ax->dev);
/* Free all AX25 frame buffers after unreg. */
kfree(ax->rbuff);
kfree(ax->xbuff);
ax->tty = NULL;
free_netdev(ax->dev);
}
......
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