openpgp: Fix parsing.

  - Previously, a signature packet with a malformed embedded signature
    would break the parsing, because the embedded signature is turned
    into an unknown packet, hence `Signature::from_reader` returns
    `Error::InvalidOperation` and so does `SubpacketArea::parse`.
    Errors from that function are handled using php_try!, but that did
    not make the packet turn into an unknown packet, but terminated
    the parsing.

  - Looking at `Subpacket::parse` revealed that there are more errors
    that would terminate parsing in the outlined way, notably
    `Error::MalformedPacket`, but there may be others.

  - Fix this by tweaking php_try! to return unknown packets on any
    `openpgp::Error`.

2 files changed, 14 insertions, 6 deletions

diff --git a/openpgp/src/parse.rs b/openpgp/src/parse.rs
index e84cca47..6121ef31 100644
--- a/openpgp/src/parse.rs
+++ b/openpgp/src/parse.rs
@@ -394,12 +394,7 @@ macro_rules! make_php_try {
                             Err(e) => e,
                         };
                         let e = match e.downcast::<Error>() {
-                            Ok(e) => match e {
-                                Error::MalformedMPI(_) =>
-                                    return $parser.error(e.into()),
-                                _ =>
-                                    e.into(),
-                            },
+                            Ok(e) => return $parser.error(e.into()),
                             Err(e) => e,
                         };
 
@@ -5519,4 +5514,17 @@ mod test {
             panic!("expected unknown packet, got: {:?}", packet);
         }
     }
+
+    /// Malformed subpackets must not cause a hard parsing error.
+    #[test]
+    fn malformed_embedded_signature() -> Result<()> {
+        let ppr = PacketParser::from_bytes(
+            crate::tests::file("edge-cases/malformed-embedded-sig.pgp"))?;
+        let packet = &ppr.unwrap().packet;
+        if let Packet::Unknown(_) = packet {
+            Ok(())
+        } else {
+            panic!("expected unknown packet, got: {:?}", packet);
+        }
+    }
 }
diff --git a/openpgp/tests/data/edge-cases/malformed-embedded-sig.pgp b/openpgp/tests/data/edge-cases/malformed-embedded-sig.pgp
new file mode 100644
index 00000000..5b2f1597
--- /dev/null
+++ b/openpgp/tests/data/edge-cases/malformed-embedded-sig.pgp