CVE-2024-49998 Information

Description

In the Linux kernel the following vulnerability has been resolved:

net: dsa: improve shutdown sequence

Alexander Sverdlin presents 2 problems during shutdown with the lan9303 driver. One is specific to lan9303 and the other just happens to reproduce there.

The first problem is that lan9303 is unique among DSA drivers in that it calls dev_get_drvdata() at rbitrary runtime\ (not probe not shutdown not remove):

phy_state_machine() -> … -> dsa_user_phy_read() -> ds->ops->phy_read() -> lan9303_phy_read() -> chip->ops->phy_read() -> lan9303_mdio_phy_read() -> dev_get_drvdata()

But we never stop the phy_state_machine() so it may continue to run after dsa_switch_shutdown(). Our common pattern in all DSA drivers is to set drvdata to NULL to suppress the remove() method that may come afterwards. But in this case it will result in an NPD.

The second problem is that the way in which we set dp->conduit->dsa_ptr = NULL; is concurrent with receive packet processing. dsa_switch_rcv() checks once whether dev->dsa_ptr is NULL but afterwards rather than continuing to use that non-NULL value dev->dsa_ptr is dereferenced again and again without NULL checks: dsa_conduit_find_user() and many other places. In between dereferences there is no locking to ensure that what was valid once continues to be valid.

Both problems have the common aspect that closing the conduit interface solves them.

In the first case dev_close(conduit) triggers the NETDEV_GOING_DOWN event in dsa_user_netdevice_event() which closes user ports as well. dsa_port_disable_rt() calls phylink_stop() which synchronously stops the phylink state machine and ds->ops->phy_read() will thus no longer call into the driver after this point.

In the second case dev_close(conduit) should do this as per Documentation/networking/driver.rst:

So it should be sufficient to ensure that later when we zeroize conduit->dsa_ptr there will be no concurrent dsa_switch_rcv() call on this conduit.

The addition of the netif_device_detach() function is to ensure that ioctls rtnetlinks and ethtool requests on the user ports no longer propagate down to the driver - we’re no longer prepared to handle them.

The race condition actually did not exist when commit 0650bf52b31f ( et: dsa: be compatible with masters which unregister on shutdown) first introduced dsa_switch_shutdown(). It was created later when we stopped unregistering the user interfaces from a bad spot and we just replaced that sequence with a racy zeroization of conduit->dsa_ptr (one which doesn’t ensure that the interfaces aren’t up).

CVSS Vector

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H

Reference

https://git.kernel.org/stable/c/ab5d3420a1120950703dbdc33698b28a6ebc3d23 https://git.kernel.org/stable/c/b4a65d479213fe84ecb14e328271251eebe69492 https://git.kernel.org/stable/c/6c24a03a61a245fe34d47582898331fa034b6ccd

Attack Complexity

HIGH

Privileges Required

LOW

User Interaction Required

LOW

Scope

NONE

Confidentiality Impact

UNCHANGED

Integrity Impact

NONE

Availability Impact

NONE

Base Score

HIGH

Base Severity

4.7