On Mon, Mar 17, 2025 at 10:52:25AM +0100, Michal Luczaj wrote:
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 <m...@rbox.co>
---
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)
I would avoid this change, especially in a patch with the Fixes tag then
to be backported.
{
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);
But here we release it, so can still a reset happen at this point,
before calling __vsock_connectible_recvmsg().
In there anyway we handle the case where transport is null, so there's
no problem, right?
The rest LTGM.
Thanks,
Stefano
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
