net/packet: fix a race in packet_set_ring() and packet_notifier()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: net/packet: fix a race in packet_set_ring() and packet_notifier() When packet_set_ring() releases po->bind_lock, another thread can run packet_notifier() and process an NETDEV_UP event. This race and the fix are both similar to that of commit 15fe076edea7 ("net/packet: fix a race in packet_bind() and packet_notifier()"). There too the packet_notifier NETDEV_UP event managed to run while a po->bind_lock critical section had to be temporarily released. And the fix was similarly to temporarily set po->num to zero to keep the socket unhooked until the lock is retaken. The po->bind_lock in packet_set_ring and packet_notifier precede the introduction of git history.

References

• https://git.kernel.org/stable/c/18f13f2a83eb81be349a9757ba2141ff1da9ad73
• https://git.kernel.org/stable/c/7da733f117533e9b2ebbd530a22ae4028713955c
• https://git.kernel.org/stable/c/ba2257034755ae773722f15f4c3ad1dcdad15ca9
• https://git.kernel.org/stable/c/7de07705007c7e34995a5599aaab1d23e762d7ca
• https://git.kernel.org/stable/c/88caf46db8239e6471413d28aabaa6b8bd552805
• https://git.kernel.org/stable/c/f2e8fcfd2b1bc754920108b7f2cd75082c5a18df
• https://git.kernel.org/stable/c/e50ccfaca9e3c671cae917dcb994831a859cf588
• https://git.kernel.org/stable/c/f1791fd7b845bea0ce9674fcf2febee7bc87a893
• https://git.kernel.org/stable/c/01d3c8417b9c1b884a8a981a3b886da556512f36
• https://blog.calif.io/p/a-race-within-a-race-exploiting-cve
• https://github.com/google/security-research/pull/339