linux-kernel - [PATCH net v2 1/3] vsock/bpf: Fix EINTR connect() racing sockmap update

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Message-Id: <20250314-vsock-trans-signal-race-v2-1-421a41f60f42@rbox.co>
Date: Fri, 14 Mar 2025 16:19:34 +0100
From: Michal Luczaj <mhal@...x.co>
To: Stefano Garzarella <sgarzare@...hat.com>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
 Simon Horman <horms@...nel.org>, "Michael S. Tsirkin" <mst@...hat.com>, 
 Bobby Eshleman <bobby.eshleman@...edance.com>, 
 Andrii Nakryiko <andrii@...nel.org>, Eduard Zingerman <eddyz87@...il.com>, 
 Mykola Lysenko <mykolal@...com>, Alexei Starovoitov <ast@...nel.org>, 
 Daniel Borkmann <daniel@...earbox.net>, 
 Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>, 
 Yonghong Song <yonghong.song@...ux.dev>, 
 John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, 
 Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
 Jiri Olsa <jolsa@...nel.org>, Shuah Khan <shuah@...nel.org>
Cc: netdev@...r.kernel.org, bpf@...r.kernel.org, 
 virtualization@...ts.linux.dev, linux-kernel@...r.kernel.org, 
 linux-kselftest@...r.kernel.org, Michal Luczaj <mhal@...x.co>
Subject: [PATCH net v2 1/3] vsock/bpf: Fix EINTR connect() racing sockmap
 update

Signal delivery during connect() may result in a disconnect of an already
TCP_ESTABLISHED socket. Problem is that such established socket might have
been placed in a sockmap before the connection was closed. We end up with a
SS_UNCONNECTED vsock in a sockmap. And this, combined with the ability to
reassign (unconnected) vsock's transport to NULL, breaks the sockmap
contract. As manifested by WARN_ON_ONCE.

connect
  / state = SS_CONNECTED /
                                sock_map_update_elem
  if signal_pending
    state = SS_UNCONNECTED

connect
  transport = NULL
                                vsock_bpf_recvmsg
                                  WARN_ON_ONCE(!vsk->transport)

Ensure the socket does not stay in sockmap.

WARNING: CPU: 8 PID: 1228 at net/vmw_vsock/vsock_bpf.c:97 vsock_bpf_recvmsg+0xb43/0xe00
CPU: 8 UID: 0 PID: 1228 Comm: a.out Not tainted 6.14.0-rc5+
RIP: 0010:vsock_bpf_recvmsg+0xb43/0xe00
 sock_recvmsg+0x1b2/0x220
 __sys_recvfrom+0x190/0x270
 __x64_sys_recvfrom+0xdc/0x1b0
 do_syscall_64+0x93/0x1b0
 entry_SYSCALL_64_after_hwframe+0x76/0x7e

Fixes: 634f1a7110b4 ("vsock: support sockmap")
Reviewed-by: Stefano Garzarella <sgarzare@...hat.com>
Signed-off-by: Michal Luczaj <mhal@...x.co>
---
 net/vmw_vsock/af_vsock.c  | 10 +++++++++-
 net/vmw_vsock/vsock_bpf.c |  1 +
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index 7e3db87ae4333cf63327ec105ca99253569bb9fe..81b1b8e9c946a646778367ab78ca180cef75ef72 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -1579,7 +1579,15 @@ static int vsock_connect(struct socket *sock, struct sockaddr *addr,

 		if (signal_pending(current)) {
 			err = sock_intr_errno(timeout);
-			sk->sk_state = sk->sk_state == TCP_ESTABLISHED ? TCP_CLOSING : TCP_CLOSE;
+			if (sk->sk_state == TCP_ESTABLISHED) {
+				/* Might have raced with a sockmap update. */
+				if (sk->sk_prot->unhash)
+					sk->sk_prot->unhash(sk);
+
+				sk->sk_state = TCP_CLOSING;
+			} else {
+				sk->sk_state = TCP_CLOSE;
+			}
 			sock->state = SS_UNCONNECTED;
 			vsock_transport_cancel_pkt(vsk);
 			vsock_remove_connected(vsk);
diff --git a/net/vmw_vsock/vsock_bpf.c b/net/vmw_vsock/vsock_bpf.c
index 07b96d56f3a577af71021b1b8132743554996c4f..c68fdaf09046b68254dac3ea70ffbe73dfa45cef 100644
--- a/net/vmw_vsock/vsock_bpf.c
+++ b/net/vmw_vsock/vsock_bpf.c
@@ -127,6 +127,7 @@ static void vsock_bpf_rebuild_protos(struct proto *prot, const struct proto *bas
 {
 	*prot        = *base;
 	prot->close  = sock_map_close;
+	prot->unhash = sock_map_unhash;
 	prot->recvmsg = vsock_bpf_recvmsg;
 	prot->sock_is_readable = sk_msg_is_readable;
 }

-- 
2.48.1