CVE-2023-52638

In the Linux kernel, the following vulnerability has been resolved:

can: j1939: prevent deadlock by changing j1939sockslock to rwlock

The following 3 locks would race against each other, causing the deadlock situation in the Syzbot bug report:

• j1939sockslock
• activesessionlist_lock
• sksessionqueue_lock

A reasonable fix is to change j1939sockslock to an rwlock, since in the rare situations where a write lock is required for the linked list that j1939sockslock is protecting, the code does not attempt to acquire any more locks. This would break the circular lock dependency, where, for example, the current thread already locks j1939sockslock and attempts to acquire sksessionqueuelock, and at the same time, another thread attempts to acquire j1939sockslock while holding sksessionqueuelock.

NOTE: This patch along does not fix the unregister_netdevice bug reported by Syzbot; instead, it solves a deadlock situation to prepare for one or more further patches to actually fix the Syzbot bug, which appears to be a reference counting problem within the j1939 codebase.

[mkl: remove unrelated newline change]