fix: Never allow a message timestamp to be a lot in the future (#5249)

We must finish what was started in
https://github.com/deltachat/deltachat-core-rust/issues/5088.

src/mimeparser.rs

@@ -208,11 +208,12 @@ impl MimeMessage {
     ) -> Result<Self> {
         let mail = mailparse::parse_mail(body)?;
 
-        let message_time = mail
+        let timestamp_rcvd = smeared_time(context);
+        let timestamp_sent = mail
             .headers
             .get_header_value(HeaderDef::Date)
             .and_then(|v| mailparse::dateparse(&v).ok())
-            .unwrap_or_default();
+            .map_or(timestamp_rcvd, |value| min(value, timestamp_rcvd + 60));
         let mut hop_info = parse_receive_headers(&mail.get_headers());
 
         let mut headers = Default::default();
@@ -279,7 +280,7 @@ impl MimeMessage {
         let private_keyring = load_self_secret_keyring(context).await?;
 
         let mut decryption_info =
-            prepare_decryption(context, &mail, &from.addr, message_time).await?;
+            prepare_decryption(context, &mail, &from.addr, timestamp_sent).await?;
 
         // Memory location for a possible decrypted message.
         let mut mail_raw = Vec::new();
@@ -325,7 +326,7 @@ impl MimeMessage {
                 let gossip_headers = mail.headers.get_all_values("Autocrypt-Gossip");
                 gossiped_keys = update_gossip_peerstates(
                     context,
-                    message_time,
+                    timestamp_sent,
                     &from.addr,
                     &recipients,
                     gossip_headers,
@@ -376,12 +377,12 @@ impl MimeMessage {
 
             // If it is not a read receipt, degrade encryption.
             if let (Some(peerstate), Ok(mail)) = (&mut decryption_info.peerstate, mail) {
-                if message_time > peerstate.last_seen_autocrypt
+                if timestamp_sent > peerstate.last_seen_autocrypt
                     && mail.ctype.mimetype != "multipart/report"
                 // Disallowing keychanges is disabled for now:
                 // && decryption_info.dkim_results.allow_keychange
                 {
-                    peerstate.degrade_encryption(message_time);
+                    peerstate.degrade_encryption(timestamp_sent);
                 }
             }
         }
@@ -395,12 +396,6 @@ impl MimeMessage {
             }
         }
 
-        let timestamp_rcvd = smeared_time(context);
-        let timestamp_sent = headers
-            .get(HeaderDef::Date.get_headername())
-            .and_then(|value| mailparse::dateparse(value).ok())
-            .map_or(timestamp_rcvd, |value| min(value, timestamp_rcvd + 60));
-
         let mut parser = MimeMessage {
             parts: Vec::new(),
             headers,
@@ -2237,6 +2232,7 @@ mod tests {
         message::{Message, MessageState, MessengerMessage},
         receive_imf::receive_imf,
         test_utils::TestContext,
+        tools::time,
     };
 
     impl AvatarAction {
@@ -3849,4 +3845,40 @@ Content-Disposition: reaction\n\
 
         Ok(())
     }
+
+    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+    async fn test_time_in_future() -> Result<()> {
+        let alice = TestContext::new_alice().await;
+
+        let beginning_time = time();
+
+        // Receive a message with a date far in the future (year 3004)
+        // I'm just going to assume that no one uses this code after the year 3000
+        let mime_message = MimeMessage::from_bytes(
+            &alice,
+            b"To: alice@example.org\n\
+              From: bob@example.net\n\
+              Date: Today, 29 February 3004 00:00:10 -800\n\
+              Message-ID: 56789@example.net\n\
+              Subject: Meeting\n\
+              Mime-Version: 1.0 (1.0)\n\
+              Content-Type: text/plain; charset=utf-8\n\
+              \n\
+              Hi",
+            None,
+        )
+        .await?;
+
+        // We do allow the time to be in the future a bit (because of unsynchronized clocks),
+        // but only 60 seconds:
+        assert!(mime_message.decryption_info.message_time <= time() + 60);
+        assert!(mime_message.decryption_info.message_time >= beginning_time + 60);
+        assert_eq!(
+            mime_message.decryption_info.message_time,
+            mime_message.timestamp_sent
+        );
+        assert!(mime_message.timestamp_rcvd <= time());
+
+        Ok(())
+    }
 }