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authorLin Ma <linma@zju.edu.cn>2021-12-17 05:13:56 +0300
committerDavid S. Miller <davem@davemloft.net>2021-12-18 15:32:48 +0300
commitb2f37aead1b82a770c48b5d583f35ec22aabb61e (patch)
tree951ca7dfdde4797b1571964c4c6d9a24d69d687e /drivers
parentaa3cc8a9e4001d50dd3e30b58257a9448b2b958b (diff)
downloadlinux-b2f37aead1b82a770c48b5d583f35ec22aabb61e.tar.xz
hamradio: improve the incomplete fix to avoid NPD
The previous commit 3e0588c291d6 ("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: Lin Ma <linma@zju.edu.cn> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/net/hamradio/mkiss.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/drivers/net/hamradio/mkiss.c b/drivers/net/hamradio/mkiss.c
index 7da2bb8a443c..edde9c3ae12b 100644
--- a/drivers/net/hamradio/mkiss.c
+++ b/drivers/net/hamradio/mkiss.c
@@ -794,14 +794,14 @@ 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);
}