[PATCH net v3] hv_sock: Report EOF instead of -EIO for FIN
From: Dexuan Cui
Date: Mon Apr 20 2026 - 23:00:40 EST
Commit f0c5827d07cb unluckily causes a regression for the FIN packet,
and the final read syscall gets an error rather than 0.
Ideally, we would want to fix hvs_channel_readable_payload() so that it
could return 0 in the FIN scenario, but it's not good for the hv_sock
driver to use the VMBus ringbuffer's cached priv_read_index, which is
internal data in the VMBus driver.
Fix the regression in hv_sock by returning 0 rather than -EIO.
In case we see a malformed/short packet, we still return -EIO.
Fixes: f0c5827d07cb ("hv_sock: Return the readable bytes in hvs_stream_has_data()")
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Ben Hillis <Ben.Hillis@xxxxxxxxxxxxx>
Reported-by: Mitchell Levy <levymitchell0@xxxxxxxxx>
Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
---
Changes since v1:
Removed the local variable 'need_refill' to make the code more
readable. Stefano, thanks!
No other change.
Changes since v2:
Added code to test the flag SEND_SHUTDOWN. Copilot, thanks!
Updated the comment and the commit messages accordingly.
net/vmw_vsock/hyperv_transport.c | 29 +++++++++++++++++++++++++----
1 file changed, 25 insertions(+), 4 deletions(-)
diff --git a/net/vmw_vsock/hyperv_transport.c b/net/vmw_vsock/hyperv_transport.c
index 069386a74557..da150de10f0d 100644
--- a/net/vmw_vsock/hyperv_transport.c
+++ b/net/vmw_vsock/hyperv_transport.c
@@ -694,7 +694,6 @@ static ssize_t hvs_stream_enqueue(struct vsock_sock *vsk, struct msghdr *msg,
static s64 hvs_stream_has_data(struct vsock_sock *vsk)
{
struct hvsock *hvs = vsk->trans;
- bool need_refill;
s64 ret;
if (hvs->recv_data_len > 0)
@@ -702,9 +701,31 @@ static s64 hvs_stream_has_data(struct vsock_sock *vsk)
switch (hvs_channel_readable_payload(hvs->chan)) {
case 1:
- need_refill = !hvs->recv_desc;
- if (!need_refill)
- return -EIO;
+ if (hvs->recv_desc) {
+ /* Here hvs->recv_data_len is 0, so hvs->recv_desc must
+ * be NULL unless it points to the 0-byte-payload FIN
+ * packet or a malformed/short packet: see
+ * hvs_update_recv_data().
+ *
+ * If hvs->recv_desc points to the FIN packet, here all
+ * the payload has been dequeued and the peer_shutdown
+ * flag is set, but hvs_channel_readable_payload() still
+ * returns 1, because the VMBus ringbuffer's read_index
+ * is not updated for the FIN packet:
+ * hvs_stream_dequeue() -> hv_pkt_iter_next() updates
+ * the cached priv_read_index but has no opportunity to
+ * update the read_index in hv_pkt_iter_close() as
+ * hvs_stream_has_data() returns 0 for the FIN packet,
+ * so it won't get dequeued.
+ *
+ * In case hvs->recv_desc points to a malformed/short
+ * packet, return -EIO.
+ */
+ if (hvs->vsk->peer_shutdown & SEND_SHUTDOWN)
+ return 0;
+ else
+ return -EIO;
+ }
hvs->recv_desc = hv_pkt_iter_first(hvs->chan);
if (!hvs->recv_desc)
--
2.49.0