can: protect the receive lists with a per-device lock

This series fixes a use-after-free in CAN_ISOTP and CAN_BCM that can be triggered when a CAN device is moved to another network namespace while a socket bound to this device is released [1].

The code of patches 1-4 is unchanged. Only the commit message of patch 4 has been updated after the Sashiko review of v4 to describe the actual NULL pointer dereference in can_rx_unregister() and the CAN_ISOTP path that reaches it.

The series is based on linux-can-next/testing, which also contains "can: raw: remove redundant NULL check before netdev_hold()" from [2].

The idea behind patch 5:

The receive lists of a CAN device are located in the device's can_ml_priv and travel with the device when it is moved to another network namespace. But they are protected by the per-netns rcvlists_lock, so the lock that protects a device's lists depends on the namespace the caller passes to can_rx_register() and can_rx_unregister(). can_rx_unregister() silently returns when this namespace does not match dev_net(dev) anymore.

isotp_release() and bcm_release() leave the netdev notifier list before they can serialize against the notifier. When the device changes its namespace in this window, their filters are not removed and the remaining receivers point to the freed socket or bcm op.

Taking RTNL in these release paths is no option, as CAN_RAW already holds RTNL while adding and removing up to CAN_RAW_FILTER_MAX filters per socket, which unprivileged users can trigger repeatedly.

Instead, patch 5 protects the receive lists where they are located: A spinlock in struct can_dev_rcv_lists protects the lists of a CAN device (initialized in can_set_ml_priv()) or the 'any' CAN device lists of a namespace (initialized in can_pernet_init()). can_rx_unregister() then finds the subscription independently of the current namespace of the device, which is kept accessible by the tracked device references the protocols already hold. The per-netns rcvlists_lock only protects the receive list statistics, for which CAN_RAW, CAN_BCM and CAN_ISOTP pass the namespace that has been used for can_rx_register().

As a consequence, CAN_RAW and CAN_ISOTP do not need RTNL in bind(), setsockopt() and release() anymore. bind() is serialized against NETDEV_UNREGISTER by publishing the device inside the RCU section of its lookup, as unlist_netdevice() and synchronize_net() precede NETDEV_UNREGISTER both on unregistration and on a namespace change. The notifiers recheck the binding under lock_sock(). As RTNL does not keep NETDEV_DOWN out of bind() anymore, bind() checks IFF_UP after publishing the bound device, with an smp_mb() pair against the notifiers, so a down transition during bind() is still reported with ENETDOWN.

Changes in v5 (details in patch 5):
- report ENETDOWN for a down transition during bind() again
- comment and kernel-doc updates
- patch 4: commit message describes the actual crash path (all from the Sashiko review of v4)

[1] https://lore.kernel.org/linux-can/[email protected]/
[2] https://lore.kernel.org/linux-can/[email protected]/

Previous versions of patch 5:
v4: https://lore.kernel.org/linux-can/[email protected]/
v3: https://lore.kernel.org/linux-can/[email protected]/
v2: https://lore.kernel.org/linux-can/[email protected]/
v1: https://lore.kernel.org/linux-can/[email protected]/

Oliver Hartkopp (4):
can: proc: skip stats calculation after reset in can_stat_update()
can: proc: remove pointers from CAN specific proc output
can: replace ARPHRD_CAN type checks with can_get_ml_priv()
can: protect the receive lists with a per-device lock

Runyu Xiao (1):
can: proc: reset pkg_stats atomics individually

 Documentation/networking/can.rst |  16 +--
 include/linux/can/can-ml.h       |   3 +
 include/linux/can/core.h         |   2 +-
 include/net/netns/can.h          |   2 +-
 net/can/af_can.c                 |  60 +++++++-----
 net/can/af_can.h                 |   2 +-
 net/can/bcm.c                    |  64 +++++-------
 net/can/gw.c                     |   9 +-
 net/can/isotp.c                  |  57 ++++++++---
 net/can/j1939/main.c             |   2 +-
 net/can/proc.c                   |  95 +++++++++++-------
 net/can/raw.c                    | 163 ++++++++++++++++++++-----------
 12 files changed, 284 insertions(+), 191 deletions(-)

2.43.0