netpoll: Fix race condition in netpoll_owner_active

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: netpoll: Fix race condition in netpoll_owner_active KCSAN detected a race condition in netpoll: BUG: KCSAN: data-race in net_rx_action / netpoll_send_skb write (marked) to 0xffff8881164168b0 of 4 bytes by interrupt on cpu 10: net_rx_action (./include/linux/netpoll.h:90 net/core/dev.c:6712 net/core/dev.c:6822) <snip> read to 0xffff8881164168b0 of 4 bytes by task 1 on cpu 2: netpoll_send_skb (net/core/netpoll.c:319 net/core/netpoll.c:345 net/core/netpoll.c:393) netpoll_send_udp (net/core/netpoll.c:?) <snip> value changed: 0x0000000a -> 0xffffffff This happens because netpoll_owner_active() needs to check if the current CPU is the owner of the lock, touching napi->poll_owner non atomically. The ->poll_owner field contains the current CPU holding the lock. Use an atomic read to check if the poll owner is the current CPU.

References

• https://git.kernel.org/stable/c/43c0ca793a18578a0f5b305dd77fcf7ed99f1265
• https://git.kernel.org/stable/c/efd29cd9c7b8369dfc7bcb34637e6bf1a188aa8e
• https://git.kernel.org/stable/c/96826b16ef9c6568d31a1f6ceaa266411a46e46c
• https://git.kernel.org/stable/c/3f1a155950a1685ffd0fd7175b3f671da8771f3d
• https://git.kernel.org/stable/c/a130e7da73ae93afdb4659842267eec734ffbd57
• https://git.kernel.org/stable/c/c2e6a872bde9912f1a7579639c5ca3adf1003916