can: netlink: can_changelink(): fix NULL pointer deref of struct can_priv::do_set_mode

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: can: netlink: can_changelink(): fix NULL pointer deref of struct can_priv::do_set_mode Andrei Lalaev reported a NULL pointer deref when a CAN device is restarted from Bus Off and the driver does not implement the struct can_priv::do_set_mode callback. There are 2 code path that call struct can_priv::do_set_mode: - directly by a manual restart from the user space, via can_changelink() - delayed automatic restart after bus off (deactivated by default) To prevent the NULL pointer deference, refuse a manual restart or configure the automatic restart delay in can_changelink() and report the error via extack to user space. As an additional safety measure let can_restart() return an error if can_priv::do_set_mode is not set instead of dereferencing it unchecked.

References

• https://git.kernel.org/stable/c/6bbcf37c5114926c99a1d1e6993a5b35689d2599
• https://git.kernel.org/stable/c/cf81a60a973358dea163f6b14062f17831ceb894
• https://git.kernel.org/stable/c/0ca816a96fdcf32644c80cbe7a82c7b6ce6ddda5
• https://git.kernel.org/stable/c/6acceb46180f9e160d4f0c56fcaf39ba562822ae
• https://git.kernel.org/stable/c/c1f3f9797c1f44a762e6f5f72520b2e520537b52