jrajahalme
commented
1 month ago This is a concurrent read/write on Conn.UDPSize in the dns library. This has not happened before due to us not trying to read and write on Conn at the same time.
The specific instance of write above indicates that the forwarded DNS request was a DNSSec one, as on current main branch the line vendor/github.com/cilium/dns/client.go:242 is:
func (c *Client) SendContext(ctx context.Context, m *Msg, co *Conn, t time.Time) error {
opt := m.IsEdns0()
// If EDNS0 is used use that for size.
if opt != nil && opt.UDPSize() >= MinMsgSize {
co.UDPSize = opt.UDPSize() <<<< HERE
}
// Otherwise use the client's configured UDP size.
if opt == nil && c.UDPSize >= MinMsgSize {
co.UDPSize = c.UDPSize
}In order to fix this we may have to assume as large as possible UDP buffer size (64k, or as large as ever needed, maybe 4k) for the shared client and change the setting of Conn.UDPSize happen only when the Conn is first created.
Client.DialContext() already sets Conn.UDPSize, so if set on the Client we could change SendContext to only change Conn.UDPSize if it is already not big enough. Besides, for the shared client setting this value after the start of the receive loop is not going to take effect anyway.
bimmlerd
seen with 54796b085eb2f8c695db74cef95521e732effacf