Merge #809: fix crash in Descriptor::parse_desc found by fuzzer

6bff186 add regression test for #806 (Andrew Poelstra)
05d3cc2 descriptor: fix key parsing error handling in parse_desc (Andrew Poelstra)

Pull request description:

  Thanks to Bruno Garcia and i-am-yuvi who independently found this crash and reported it to me.

  Fixes #806

  Needs backport.

ACKs for top commit:
  brunoerg:
    code review ACK 6bff186; haven't tested
  i-am-yuvi:
    Tested and Code Review ACK 6bff186
  sanket1729:
    ACK 6bff186

Tree-SHA512: abd386758fc6e2a408c2de7bb6be61274a4252cafd97130bd449ce2fb23180cffa416ffe7393a809c69cf541186f3866aaa9fef635ce57fbc4bcf455a5b287c0

Author: apoelstra

src/descriptor/mod.rs

@@ -771,7 +771,7 @@ impl Descriptor<DescriptorPublicKey> {
         let descriptor = Descriptor::<String>::from_str(s)?;
         let descriptor = descriptor
             .translate_pk(&mut keymap_pk)
-            .map_err(|e| e.expect_translator_err("No Outer context errors"))?;
+            .map_err(TranslateErr::flatten)?;
 
         Ok((descriptor, keymap_pk.0))
     }
@@ -2168,4 +2168,19 @@ pk(03f28773c2d975288bc7d1d205c3748651b075fbc6610e58cddeeddf8f19405aa8))";
         Desc::from_str(&format!("tr({},pk({}))", x_only_key, uncomp_key)).unwrap_err();
         Desc::from_str(&format!("tr({},pk({}))", x_only_key, x_only_key)).unwrap();
     }
+
+    #[test]
+    fn regression_806() {
+        let secp = secp256k1::Secp256k1::signing_only();
+        type Desc = Descriptor<DescriptorPublicKey>;
+        // OK
+        Desc::from_str("pkh(111111111111111111111111111111110000008375319363688624584A111111)")
+            .unwrap_err();
+        // ERR: crashes in translate_pk
+        Desc::parse_descriptor(
+            &secp,
+            "pkh(111111111111111111111111111111110000008375319363688624584A111111)",
+        )
+        .unwrap_err();
+    }
 }

src/lib.rs

@@ -356,10 +356,22 @@ impl<E> TranslateErr<E> {
     ///
     /// This function will panic if the Error is OutError.
     pub fn expect_translator_err(self, msg: &str) -> E {
-        if let Self::TranslatorErr(v) = self {
-            v
-        } else {
-            panic!("{}", msg)
+        match self {
+            Self::TranslatorErr(v) => v,
+            Self::OuterError(ref e) => {
+                panic!("Unexpected Miniscript error when translating: {}\nMessage: {}", e, msg)
+            }
+        }
+    }
+}
+
+impl TranslateErr<Error> {
+    /// If we are doing a translation where our "outer error" is the generic
+    /// Miniscript error, eliminate the `TranslateErr` type which is just noise.
+    pub fn flatten(self) -> Error {
+        match self {
+            Self::TranslatorErr(e) => e,
+            Self::OuterError(e) => e,
         }
     }
 }