fix: Don't treat forged outgoing messages as Autocrypt-encrypted

src/decrypt.rs

@@ -12,7 +12,7 @@ use crate::authres::{self, DkimResults};
 use crate::contact::addr_cmp;
 use crate::context::Context;
 use crate::headerdef::{HeaderDef, HeaderDefMap};
-use crate::key::{DcKey, Fingerprint, SignedPublicKey, SignedSecretKey};
+use crate::key::{self, DcKey, Fingerprint, SignedPublicKey, SignedSecretKey};
 use crate::peerstate::Peerstate;
 use crate::pgp;
 
@@ -264,16 +264,22 @@ pub(crate) fn validate_detached_signature<'a, 'b>(
     }
 }
 
-pub(crate) fn keyring_from_peerstate(peerstate: Option<&Peerstate>) -> Vec<SignedPublicKey> {
+/// Returns public keyring for `peerstate`.
+pub(crate) async fn keyring_from_peerstate(
+    context: &Context,
+    peerstate: Option<&Peerstate>,
+) -> Result<Vec<SignedPublicKey>> {
     let mut public_keyring_for_validate = Vec::new();
     if let Some(peerstate) = peerstate {
         if let Some(key) = &peerstate.public_key {
             public_keyring_for_validate.push(key.clone());
         } else if let Some(key) = &peerstate.gossip_key {
             public_keyring_for_validate.push(key.clone());
+        } else if context.is_self_addr(&peerstate.addr).await? {
+            public_keyring_for_validate = key::load_self_public_keyring(context).await?;
         }
     }
-    public_keyring_for_validate
+    Ok(public_keyring_for_validate)
 }
 
 /// Applies Autocrypt header to Autocrypt peer state and saves it into the database.
@@ -292,6 +298,7 @@ pub(crate) async fn get_autocrypt_peerstate(
     message_time: i64,
     allow_change: bool,
 ) -> Result<Option<Peerstate>> {
+    let allow_change = allow_change && !context.is_self_addr(from).await?;
     let mut peerstate;
 
     // Apply Autocrypt header

src/key.rs

@@ -101,6 +101,25 @@ pub(crate) async fn load_self_public_key(context: &Context) -> Result<SignedPubl
     }
 }
 
+/// Returns our own public keyring.
+pub(crate) async fn load_self_public_keyring(context: &Context) -> Result<Vec<SignedPublicKey>> {
+    let keys = context
+        .sql
+        .query_map(
+            r#"SELECT public_key
+               FROM keypairs
+               ORDER BY id=(SELECT value FROM config WHERE keyname='key_id') DESC"#,
+            (),
+            |row| row.get::<_, Vec<u8>>(0),
+            |keys| keys.collect::<Result<Vec<_>, _>>().map_err(Into::into),
+        )
+        .await?
+        .into_iter()
+        .filter_map(|bytes| SignedPublicKey::from_slice(&bytes).log_err(context).ok())
+        .collect();
+    Ok(keys)
+}
+
 pub(crate) async fn load_self_secret_key(context: &Context) -> Result<SignedSecretKey> {
     let private_key = context
         .sql

src/mimeparser.rs

@@ -304,7 +304,8 @@ impl MimeMessage {
         hop_info += "\n\n";
         hop_info += &decryption_info.dkim_results.to_string();
 
-        let public_keyring = keyring_from_peerstate(decryption_info.peerstate.as_ref());
+        let public_keyring =
+            keyring_from_peerstate(context, decryption_info.peerstate.as_ref()).await?;
         let (mail, mut signatures, encrypted) = match tokio::task::block_in_place(|| {
             try_decrypt(&mail, &private_keyring, &public_keyring)
         }) {

src/peerstate.rs

@@ -16,6 +16,7 @@ use crate::message::Message;
 use crate::mimeparser::SystemMessage;
 use crate::sql::Sql;
 use crate::stock_str;
+use crate::tools;
 
 /// Type of the public key stored inside the peerstate.
 #[derive(Debug)]
@@ -165,6 +166,9 @@ impl Peerstate {
 
     /// Loads peerstate corresponding to the given address from the database.
     pub async fn from_addr(context: &Context, addr: &str) -> Result<Option<Peerstate>> {
+        if context.is_self_addr(addr).await? {
+            return Ok(Some(Peerstate::get_self_stub(addr)));
+        }
         let query = "SELECT addr, last_seen, last_seen_autocrypt, prefer_encrypted, public_key, \
                      gossip_timestamp, gossip_key, public_key_fingerprint, gossip_key_fingerprint, \
                      verified_key, verified_key_fingerprint, \
@@ -182,6 +186,7 @@ impl Peerstate {
         context: &Context,
         fingerprint: &Fingerprint,
     ) -> Result<Option<Peerstate>> {
+        // NOTE: If it's our key fingerprint, this returns None currently.
         let query = "SELECT addr, last_seen, last_seen_autocrypt, prefer_encrypted, public_key, \
                      gossip_timestamp, gossip_key, public_key_fingerprint, gossip_key_fingerprint, \
                      verified_key, verified_key_fingerprint, \
@@ -206,6 +211,9 @@ impl Peerstate {
         fingerprint: &Fingerprint,
         addr: &str,
     ) -> Result<Option<Peerstate>> {
+        if context.is_self_addr(addr).await? {
+            return Ok(Some(Peerstate::get_self_stub(addr)));
+        }
         let query = "SELECT addr, last_seen, last_seen_autocrypt, prefer_encrypted, public_key, \
                      gossip_timestamp, gossip_key, public_key_fingerprint, gossip_key_fingerprint, \
                      verified_key, verified_key_fingerprint, \
@@ -221,6 +229,34 @@ impl Peerstate {
         Self::from_stmt(context, query, (&fp, &addr, &fp)).await
     }
 
+    /// Returns peerstate stub for self `addr`.
+    ///
+    /// Needed for [`crate::decrypt::keyring_from_peerstate()`] which returns a keyring of all our
+    /// pubkeys for such a stub so that we can check if a message is signed by us.
+    fn get_self_stub(addr: &str) -> Self {
+        let now = tools::time();
+        // We can have multiple pubkeys, just make the corresponding fields None.
+        Self {
+            addr: addr.to_string(),
+            last_seen: now,
+            last_seen_autocrypt: now,
+            prefer_encrypt: EncryptPreference::Mutual,
+            public_key: None,
+            public_key_fingerprint: None,
+            gossip_key: None,
+            gossip_key_fingerprint: None,
+            gossip_timestamp: 0,
+            verified_key: None,
+            verified_key_fingerprint: None,
+            verifier: None,
+            secondary_verified_key: None,
+            secondary_verified_key_fingerprint: None,
+            secondary_verifier: None,
+            backward_verified_key_id: None,
+            fingerprint_changed: false,
+        }
+    }
+
     async fn from_stmt(
         context: &Context,
         query: &str,