Linux Kernel TCP SYN-ACK Process Context Vulnerability

A vulnerability in the Linux kernel's TCP implementation allows the tcp_rtx_synack() function to be called from process context. This change can lead to the tcp_make_synack() function being invoked in a way that disrupts per-CPU variables while preemption is enabled, causing a kernel BUG. The issue arises because __TCP_INC_STATS() is called in a preemptible context, which is unsafe.

Impact

The vulnerability can lead to a kernel BUG due to improper handling of per-CPU variables in a preemptible context, potentially causing system instability or crashes.