CVE-2022-49372

In the Linux kernel, the following vulnerability has been resolved:

tcp: tcp_rtx_synack() can be called from process context

Laurent reported the enclosed report [1]

This bug triggers with following coditions:

0. Kernel built with CONFIG_DEBUG_PREEMPT=y

1. A new passive FastOpen TCP socket is created. This FO socket waits for an ACK coming from client to be a complete ESTABLISHED one.

2. A socket operation on this socket goes through lock_sock() release_sock() dance.

3. While the socket is owned by the user in step 2), a retransmit of the SYN is received and stored in socket backlog.

4. At release_sock() time, the socket backlog is processed while in process context.

5. A SYNACK packet is cooked in response of the SYN retransmit.

6. -> tcp_rtx_synack() is called in process context.

Before blamed commit, tcp_rtx_synack() was always called from BH handler, from a timer handler.

Fix this by using TCP_INC_STATS() & NET_INC_STATS() which do not assume caller is in non preemptible context.

[1] BUG: using __this_cpu_add() in preemptible [00000000] code: epollpep/2180 caller is tcp_rtx_synack.part.0+0x36/0xc0 CPU: 10 PID: 2180 Comm: epollpep Tainted: G OE 5.16.0-0.bpo.4-amd64 #1 Debian 5.16.12-1~bpo11+1 Hardware name: Supermicro SYS-5039MC-H8TRF/X11SCD-F, BIOS 1.7 11/23/2021 Call Trace: dump_stack_lvl+0x48/0x5e check_preemption_disabled+0xde/0xe0 tcp_rtx_synack.part.0+0x36/0xc0 tcp_rtx_synack+0x8d/0xa0 ? kmem_cache_alloc+0x2e0/0x3e0 ? apparmor_file_alloc_security+0x3b/0x1f0 inet_rtx_syn_ack+0x16/0x30 tcp_check_req+0x367/0x610 tcp_rcv_state_process+0x91/0xf60 ? get_nohz_timer_target+0x18/0x1a0 ? lock_timer_base+0x61/0x80 ? preempt_count_add+0x68/0xa0 tcp_v4_do_rcv+0xbd/0x270 __release_sock+0x6d/0xb0 release_sock+0x2b/0x90 sock_setsockopt+0x138/0x1140 ? __sys_getsockname+0x7e/0xc0 ? aa_sk_perm+0x3e/0x1a0 __sys_setsockopt+0x198/0x1e0 __x64_sys_setsockopt+0x21/0x30 do_syscall_64+0x38/0xc0 entry_SYSCALL_64_after_hwframe+0x44/0xae

Affected Software

References

• https://git.kernel.org/stable/c/0a0f7f84148445c9f02f226928803a870139d820
• https://git.kernel.org/stable/c/0a375c822497ed6ad6b5da0792a12a6f1af10c0b
• https://git.kernel.org/stable/c/3db889f883e65bbd3b1401279bfc1e9ed255c481
• https://git.kernel.org/stable/c/58bd38cbc961fd799842b7be8c5222310f04b908
• https://git.kernel.org/stable/c/88cd232146207ff1d41dededed5e77c0d4438113
• https://git.kernel.org/stable/c/bdc28a8fb43cc476e33b11519235adb816ce00e8
• https://git.kernel.org/stable/c/c348b0f8d035fc4bdc040796889beec7218bd1b8
• https://git.kernel.org/stable/c/d05c2fdf8e10528bb6751bd95243e862d5402a9b
• https://git.kernel.org/stable/c/d8e1bc6029acac796293310aacef7b7336f35b6a