can: j1939: prevent deadlock by changing j1939_socks_lock to rwlock

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: can: j1939: prevent deadlock by changing j1939_socks_lock to rwlock The following 3 locks would race against each other, causing the deadlock situation in the Syzbot bug report: - j1939_socks_lock - active_session_list_lock - sk_session_queue_lock A reasonable fix is to change j1939_socks_lock to an rwlock, since in the rare situations where a write lock is required for the linked list that j1939_socks_lock 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 j1939_socks_lock and attempts to acquire sk_session_queue_lock, and at the same time, another thread attempts to acquire j1939_socks_lock while holding sk_session_queue_lock. 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]

References

• https://git.kernel.org/stable/c/03358aba991668d3bb2c65b3c82aa32c36851170
• https://git.kernel.org/stable/c/aedda066d717a0b4335d7e0a00b2e3a61e40afcf
• https://git.kernel.org/stable/c/26dfe112ec2e95fe0099681f6aec33da13c2dd8e
• https://git.kernel.org/stable/c/559b6322f9480bff68cfa98d108991e945a4f284
• https://git.kernel.org/stable/c/6cdedc18ba7b9dacc36466e27e3267d201948c8d