tcp: tcp_make_synack() can be called from process context

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: tcp: tcp_make_synack() can be called from process context tcp_rtx_synack() now could be called in process context as explained in 0a375c822497 ("tcp: tcp_rtx_synack() can be called from process context"). tcp_rtx_synack() might call tcp_make_synack(), which will touch per-CPU variables with preemption enabled. This causes the following BUG: BUG: using __this_cpu_add() in preemptible [00000000] code: ThriftIO1/5464 caller is tcp_make_synack+0x841/0xac0 Call Trace: <TASK> dump_stack_lvl+0x10d/0x1a0 check_preemption_disabled+0x104/0x110 tcp_make_synack+0x841/0xac0 tcp_v6_send_synack+0x5c/0x450 tcp_rtx_synack+0xeb/0x1f0 inet_rtx_syn_ack+0x34/0x60 tcp_check_req+0x3af/0x9e0 tcp_rcv_state_process+0x59b/0x2030 tcp_v6_do_rcv+0x5f5/0x700 release_sock+0x3a/0xf0 tcp_sendmsg+0x33/0x40 ____sys_sendmsg+0x2f2/0x490 __sys_sendmsg+0x184/0x230 do_syscall_64+0x3d/0x90 Avoid calling __TCP_INC_STATS() with will touch per-cpu variables. Use TCP_INC_STATS() which is safe to be called from context switch.

References

• https://git.kernel.org/stable/c/d493d4fe88195a144d6a277a90062a7534ed2192
• https://git.kernel.org/stable/c/e23ca307745be3df7fe9762f3e2a7e311a57852e
• https://git.kernel.org/stable/c/442aa78ed70188b21ccd8669738448702c0a3281
• https://git.kernel.org/stable/c/77ad58bca0119e8cc3e0e9d91a3f22caa66e4dfa
• https://git.kernel.org/stable/c/ad07290d63ff6689f50565b02f5b6f34ec15a5ca
• https://git.kernel.org/stable/c/9180aa4622a720b433e842b4d3aa34d73eec577a
• https://git.kernel.org/stable/c/7613cde8c0c1f02a7ec2e1d536c01b65b135fc1c
• https://git.kernel.org/stable/c/bced3f7db95ff2e6ca29dc4d1c9751ab5e736a09