From a7cc687c7bab91b9e525d9b91dc9d358afca5a28 Mon Sep 17 00:00:00 2001
From: Rasmus Dahlberg <rgdd@glasklarteknik.se>
Date: Sun, 5 Jan 2025 14:34:04 +0100
Subject: fix: Don't accept timestamps that shrink

---
 internal/monitor/tail.go | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/internal/monitor/tail.go b/internal/monitor/tail.go
index 98ce4e0..2ad8135 100644
--- a/internal/monitor/tail.go
+++ b/internal/monitor/tail.go
@@ -136,6 +136,9 @@ func (t *tail) nextConsistentState(ctx context.Context, state State) (State, err
 	if err != nil {
 		return State{}, fmt.Errorf("%s: get-sth: %v", t.checker.BaseURI(), err)
 	}
+	if sth.Timestamp < state.Timestamp {
+		return State{}, fmt.Errorf("%s: get-sth: timestamp is shrinking", t.checker.BaseURI())
+	}
 	sth.LogID = state.SignedTreeHead.LogID
 	oldSize := state.TreeSize
 	oldRoot := state.SHA256RootHash
-- 
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