The sockmap feature allows bpf syscall from userspace, or based on bpf sockops, replacing the sk_prot of sockets during protocol stack processing with sockmap's custom read/write interfaces. ''' tcp_rcv_state_process() syn_recv_sock()/subflow_syn_recv_sock() tcp_init_transfer(BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB) bpf_skops_established <== sockops bpf_sock_map_update(sk) <== call bpf helper tcp_bpf_update_proto() <== update sk_prot '''
When the server has MPTCP enabled but the client sends a TCP SYN without MPTCP, subflow_syn_recv_sock() performs a fallback on the subflow, replacing the subflow sk's sk_prot with the native sk_prot. ''' subflow_syn_recv_sock() subflow_ulp_fallback() subflow_drop_ctx() mptcp_subflow_ops_undo_override() '''
Then, this subflow can be normally used by sockmap, which replaces the native sk_prot with sockmap's custom sk_prot. The issue occurs when the user executes accept::mptcp_stream_accept::mptcp_fallback_tcp_ops(). Here, it uses sk->sk_prot to compare with the native sk_prot, but this is incorrect when sockmap is used, as we may incorrectly set sk->sk_socket->ops.
This fix uses the more generic sk_family for the comparison instead.
Additionally, this also prevents a WARNING from occurring:
------------[ cut here ]------------ WARNING: CPU: 1 PID: 388 at net/mptcp/protocol.c:68 \ mptcp_stream_accept+0x34c/0x380 Modules linked in: RIP: 0010:mptcp_stream_accept+0x34c/0x380 RSP: 0018:ffffc90000cf3cf8 EFLAGS: 00010202 PKRU: 55555554 Call Trace: <TASK> do_accept+0xeb/0x190 ? __x64_sys_pselect6+0x61/0x80 ? _raw_spin_unlock+0x12/0x30 ? alloc_fd+0x11e/0x190 __sys_accept4+0x8c/0x100 __x64_sys_accept+0x1f/0x30 x64_sys_call+0x202f/0x20f0 do_syscall_64+0x72/0x9a0 ? switch_fpu_return+0x60/0xf0 ? irqentry_exit_to_user_mode+0xdb/0x1e0 ? irqentry_exit+0x3f/0x50 ? clear_bhb_loop+0x50/0xa0 ? clear_bhb_loop+0x50/0xa0 ? clear_bhb_loop+0x50/0xa0 entry_SYSCALL_64_after_hwframe+0x76/0x7e </TASK> ---[ end trace 0000000000000000 ]---
result from ./scripts/decode_stacktrace.sh: ------------[ cut here ]------------ WARNING: CPU: 0 PID: 337 at net/mptcp/protocol.c:68 mptcp_stream_accept \ (net-next/net/mptcp/protocol.c:4005) Modules linked in: ...
PKRU: 55555554 Call Trace: <TASK> do_accept (net-next/net/socket.c:1989) __sys_accept4 (net-next/net/socket.c:2028 net-next/net/socket.c:2057) __x64_sys_accept (net-next/net/socket.c:2067) x64_sys_call (net-next/arch/x86/entry/syscall_64.c:41) do_syscall_64 (net-next/arch/x86/entry/syscall_64.c:63 \ net-next/arch/x86/entry/syscall_64.c:94) entry_SYSCALL_64_after_hwframe (net-next/arch/x86/entry/entry_64.S:130) RIP: 0033:0x7f87ac92b83d
---[ end trace 0000000000000000 ]---
Fixes: 0b4f33def7bb ("mptcp: fix tcp fallback crash") Cc: stable@vger.kernel.org Signed-off-by: Jiayuan Chen jiayuan.chen@linux.dev Reviewed-by: Jakub Sitnicki jakub@cloudflare.com --- net/mptcp/protocol.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c index 4cd5df01446e..b5e5e130b158 100644 --- a/net/mptcp/protocol.c +++ b/net/mptcp/protocol.c @@ -61,11 +61,13 @@ static u64 mptcp_wnd_end(const struct mptcp_sock *msk)
static const struct proto_ops *mptcp_fallback_tcp_ops(const struct sock *sk) { + unsigned short family = READ_ONCE(sk->sk_family); + #if IS_ENABLED(CONFIG_MPTCP_IPV6) - if (sk->sk_prot == &tcpv6_prot) + if (family == AF_INET6) return &inet6_stream_ops; #endif - WARN_ON_ONCE(sk->sk_prot != &tcp_prot); + WARN_ON_ONCE(family != AF_INET); return &inet_stream_ops; }