openpgp: Do not try to add subpackets to v3 signatures.

  - When we verify signatures, we sometimes add information to the
    signature's unhashed subpacket area.  This doesn't work for v3
    signatures, as those don't have subpackets.

1 files changed, 5 insertions, 0 deletions

diff --git a/openpgp/src/packet/signature.rs b/openpgp/src/packet/signature.rs
index 4862f6a3..39d8ce96 100644
--- a/openpgp/src/packet/signature.rs
+++ b/openpgp/src/packet/signature.rs
@@ -2454,6 +2454,11 @@ impl crate::packet::Signature {
             return Ok(());
         }
 
+        if self.version() == 3 {
+            return Err(Error::InvalidOperation(
+                "cannot add information to v3 signature".into()).into());
+        }
+
         /// Makes an authenticated subpacket.
         fn authenticated_subpacket(v: SubpacketValue) -> Result<Subpacket> {
             let mut p = Subpacket::new(v, false)?;