netdev - [PATCH net] net: devlink: fix UAF in devlink_compat_running

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Date:   Tue, 22 Nov 2022 20:10:48 +0800
From:   Yang Yingliang <yangyingliang@...wei.com>
To:     <netdev@...r.kernel.org>
CC:     <jiri@...dia.com>, <davem@...emloft.net>, <edumazet@...gle.com>,
        <kuba@...nel.org>, <pabeni@...hat.com>
Subject: [PATCH net] net: devlink: fix UAF in devlink_compat_running_version()

I got a UAF report as following when doing fault injection test:

BUG: KASAN: use-after-free in devlink_compat_running_version+0x5b9/0x6a0
Read of size 8 at addr ffff88810ac591f0 by task systemd-udevd/458

CPU: 2 PID: 458 Comm: systemd-udevd Not tainted 6.1.0-rc5-00155-ga9d2b54dd4e7-dirty #1359
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
Call Trace:
 <TASK>
 kasan_report+0x90/0x190
 devlink_compat_running_version+0x5b9/0x6a0
 dev_ethtool+0x2ca/0x340
 dev_ioctl+0x16c/0xff0
 sock_do_ioctl+0x1ae/0x220

Allocated by task 456:
 kasan_save_stack+0x1c/0x40
 kasan_set_track+0x21/0x30
 __kasan_kmalloc+0x7e/0x90
 __kmalloc+0x59/0x1b0
 devlink_alloc_ns+0xf7/0xa10
 nsim_drv_probe+0xa8/0x150 [netdevsim]
 really_probe+0x1ff/0x660

Freed by task 456:
 kasan_save_stack+0x1c/0x40
 kasan_set_track+0x21/0x30
 kasan_save_free_info+0x2a/0x50
 __kasan_slab_free+0x102/0x190
 __kmem_cache_free+0xca/0x400
 nsim_drv_probe.cold.31+0x2af/0xf62 [netdevsim]
 really_probe+0x1ff/0x660

It happened like this:

processor A							processor B
nsim_drv_probe()
  devlink_alloc_ns()
  nsim_dev_port_add_all()
    __nsim_dev_port_add() // add eth1 successful
								dev_ethtool()
								  ethtool_get_drvinfo(eth1)
								    netdev_to_devlink_get(eth1)
								      devlink_try_get() // get devlink here
    __nsim_dev_port_add() // add eth2 failed, goto error
      devlink_free() // it's called in the error path
								  devlink_compat_running_version() <- causes UAF
  devlink_register() // it's in normal path, not called yet

There is two ports to add in nsim_dev_port_add_all(), if first
port is added successful, the devlink is visable and can be get
by devlink_try_get() on another cpu, but it is not registered
yet. And then the second port is failed to added, in the error
path, devlink_free() is called, at last it causes UAF.

Add check in devlink_try_get(), if the 'devlink' is not registered
it returns NULL to avoid UAF like this case.

Fixes: a62fdbbe9403 ("netdevsim: implement ndo_get_devlink_port")
Reported-by: Zhengchao Shao <shaozhengchao@...wei.com>
Signed-off-by: Yang Yingliang <yangyingliang@...wei.com>
---
 net/core/devlink.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/core/devlink.c b/net/core/devlink.c
index 89baa7c0938b..6453ac0558fb 100644
--- a/net/core/devlink.c
+++ b/net/core/devlink.c
@@ -250,6 +250,9 @@ void devlink_put(struct devlink *devlink)
 
 struct devlink *__must_check devlink_try_get(struct devlink *devlink)
 {
+	 if (!xa_get_mark(&devlinks, devlink->index, DEVLINK_REGISTERED))
+		return NULL;
+
 	if (refcount_inc_not_zero(&devlink->refcount))
 		return devlink;
 	return NULL;
-- 
2.25.1