[PATCH net v2 3/3] vsock/bpf: Fix bpf recvmsg() racing transport reassignment

From: Michal Luczaj
Date: Fri Mar 14 2025 - 11:21:31 EST


Signal delivery during connect() may lead to a disconnect of an already
established socket. That involves removing socket from any sockmap and
resetting state to SS_UNCONNECTED. While it correctly restores socket's
proto, a call to vsock_bpf_recvmsg() might have been already under way in
another thread. If the connect()ing thread reassigns the vsock transport to
NULL, the recvmsg()ing thread may trigger a WARN_ON_ONCE.

connect
/ state = SS_CONNECTED /
sock_map_update_elem
vsock_bpf_recvmsg
psock = sk_psock_get()
lock sk
if signal_pending
unhash
sock_map_remove_links
state = SS_UNCONNECTED
release sk

connect
transport = NULL
lock sk
WARN_ON_ONCE(!vsk->transport)

Protect recvmsg() from racing against transport reassignment. Enforce the
sockmap invariant that psock implies transport: lock socket before getting
psock.

WARNING: CPU: 9 PID: 1222 at net/vmw_vsock/vsock_bpf.c:92 vsock_bpf_recvmsg+0xb55/0xe00
CPU: 9 UID: 0 PID: 1222 Comm: a.out Not tainted 6.14.0-rc5+
RIP: 0010:vsock_bpf_recvmsg+0xb55/0xe00
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")
Signed-off-by: Michal Luczaj <mhal@xxxxxxx>
---
net/vmw_vsock/vsock_bpf.c | 23 +++++++++++++++--------
1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/net/vmw_vsock/vsock_bpf.c b/net/vmw_vsock/vsock_bpf.c
index c68fdaf09046b68254dac3ea70ffbe73dfa45cef..5138195d91fb258d4bc09b48e80e13651d62863a 100644
--- a/net/vmw_vsock/vsock_bpf.c
+++ b/net/vmw_vsock/vsock_bpf.c
@@ -73,28 +73,35 @@ static int __vsock_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int
return err;
}

-static int vsock_bpf_recvmsg(struct sock *sk, struct msghdr *msg,
- size_t len, int flags, int *addr_len)
+static int vsock_bpf_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
+ int flags, int *addr_len)
{
struct sk_psock *psock;
struct vsock_sock *vsk;
int copied;

+ /* Since signal delivery during connect() may reset the state of socket
+ * that's already in a sockmap, take the lock before checking on psock.
+ * This serializes a possible transport reassignment, protecting this
+ * function from running with NULL transport.
+ */
+ lock_sock(sk);
+
psock = sk_psock_get(sk);
- if (unlikely(!psock))
+ if (unlikely(!psock)) {
+ release_sock(sk);
return __vsock_recvmsg(sk, msg, len, flags);
+ }

- lock_sock(sk);
vsk = vsock_sk(sk);
-
if (WARN_ON_ONCE(!vsk->transport)) {
copied = -ENODEV;
goto out;
}

if (vsock_has_data(sk, psock) && sk_psock_queue_empty(psock)) {
- release_sock(sk);
sk_psock_put(sk, psock);
+ release_sock(sk);
return __vsock_recvmsg(sk, msg, len, flags);
}

@@ -108,8 +115,8 @@ static int vsock_bpf_recvmsg(struct sock *sk, struct msghdr *msg,
}

if (sk_psock_queue_empty(psock)) {
- release_sock(sk);
sk_psock_put(sk, psock);
+ release_sock(sk);
return __vsock_recvmsg(sk, msg, len, flags);
}

@@ -117,8 +124,8 @@ static int vsock_bpf_recvmsg(struct sock *sk, struct msghdr *msg,
}

out:
- release_sock(sk);
sk_psock_put(sk, psock);
+ release_sock(sk);

return copied;
}

--
2.48.1