Merge #13002: Do not treat bare multisig outputs as IsMine unless watched

7d0f80b Use anonymous namespace instead of static functions (Pieter Wuille)
b61fb71 Mention removal of bare multisig IsMine in release notes (Pieter Wuille)
9c2a8b8 Do not treat bare multisig as IsMine (Pieter Wuille)
08f3228 Optimization: only test for witness scripts at top level (Pieter Wuille)
3619735 Track difference between scriptPubKey and P2SH execution in IsMine (Pieter Wuille)
ac6ec62 Switch to a private version of SigVersion inside IsMine (Pieter Wuille)
19fc973 Do not expose SigVersion argument to IsMine (Pieter Wuille)
fb1dfbb Remove unused IsMine overload (Pieter Wuille)
952d821 Make CScript -> CScriptID conversion explicit (Pieter Wuille)

Pull request description:

  Currently our wallet code will treat bare multisig outputs (meaning scriptPubKeys with multiple public keys + `OP_CHECKMULTISIG` operator in it) as ours without the user asking for it, as long as all private keys in it are in our wallet.

  This is a pointless feature. As it only works when all private keys are in one place, it's useless compared to single key outputs (P2PK, P2PKH, P2WPKH, P2SH-P2WPKH), and worse in terms of space, cost, UTXO size, and ability to test (due to lack of address format for them).

  Furthermore, they are problematic in that producing a list of all `scriptPubKeys` we accept is not tractable (it involves all combinations of all public keys that are ours). In further wallet changes I'd like to move to a model where all scriptPubKeys that are treated as ours are explicit, rather than defined by whatever keys we have. The current behavior of the wallet is very hard to model in such a design, so I'd like to get rid of it.

  I think there are two options:
  * Remove it entirely (do not ever accept bare multisig outputs as ours, unless watched)
  * Only accept bare multisig outputs in situations where the P2SH version of that output would also be acceptable

  This PR implements the first option. The second option was explored in #12874.

Tree-SHA512: 917ed45b3cac864cee53e27f9a3e900390c576277fbd6751b1250becea04d692b3b426fa09065a3399931013bd579c4f3dbeeb29d51d19ed0c64da75d430ad9a

3 files changed, 55 insertions, 32 deletions

diff --git a/src/script/ismine.cpp b/src/script/ismine.cpp
index b826bcfe20..fefa02fdef 100644
--- a/src/script/ismine.cpp
+++ b/src/script/ismine.cpp
@@ -13,34 +13,36 @@
 
 typedef std::vector<unsigned char> valtype;
 
-static bool HaveKeys(const std::vector<valtype>& pubkeys, const CKeyStore& keystore)
-{
-    for (const valtype& pubkey : pubkeys) {
-        CKeyID keyID = CPubKey(pubkey).GetID();
-        if (!keystore.HaveKey(keyID)) return false;
-    }
-    return true;
-}
+namespace {
 
-isminetype IsMine(const CKeyStore& keystore, const CScript& scriptPubKey, SigVersion sigversion)
+/**
+ * This is an enum that tracks the execution context of a script, similar to
+ * SigVersion in script/interpreter. It is separate however because we want to
+ * distinguish between top-level scriptPubKey execution and P2SH redeemScript
+ * execution (a distinction that has no impact on consensus rules).
+ */
+enum class IsMineSigVersion
 {
-    bool isInvalid = false;
-    return IsMine(keystore, scriptPubKey, isInvalid, sigversion);
-}
+    TOP = 0,        //! scriptPubKey execution
+    P2SH = 1,       //! P2SH redeemScript
+    WITNESS_V0 = 2  //! P2WSH witness script execution
+};
 
-isminetype IsMine(const CKeyStore& keystore, const CTxDestination& dest, SigVersion sigversion)
+bool PermitsUncompressed(IsMineSigVersion sigversion)
 {
-    bool isInvalid = false;
-    return IsMine(keystore, dest, isInvalid, sigversion);
+    return sigversion == IsMineSigVersion::TOP || sigversion == IsMineSigVersion::P2SH;
 }
 
-isminetype IsMine(const CKeyStore &keystore, const CTxDestination& dest, bool& isInvalid, SigVersion sigversion)
+bool HaveKeys(const std::vector<valtype>& pubkeys, const CKeyStore& keystore)
 {
-    CScript script = GetScriptForDestination(dest);
-    return IsMine(keystore, script, isInvalid, sigversion);
+    for (const valtype& pubkey : pubkeys) {
+        CKeyID keyID = CPubKey(pubkey).GetID();
+        if (!keystore.HaveKey(keyID)) return false;
+    }
+    return true;
 }
 
-isminetype IsMine(const CKeyStore &keystore, const CScript& scriptPubKey, bool& isInvalid, SigVersion sigversion)
+isminetype IsMineInner(const CKeyStore& keystore, const CScript& scriptPubKey, bool& isInvalid, IsMineSigVersion sigversion)
 {
     isInvalid = false;
 
@@ -61,7 +63,7 @@ isminetype IsMine(const CKeyStore &keystore, const CScript& scriptPubKey, bool&
         break;
     case TX_PUBKEY:
         keyID = CPubKey(vSolutions[0]).GetID();
-        if (sigversion != SigVersion::BASE && vSolutions[0].size() != 33) {
+        if (!PermitsUncompressed(sigversion) && vSolutions[0].size() != 33) {
             isInvalid = true;
             return ISMINE_NO;
         }
@@ -70,20 +72,20 @@ isminetype IsMine(const CKeyStore &keystore, const CScript& scriptPubKey, bool&
         break;
     case TX_WITNESS_V0_KEYHASH:
     {
-        if (!keystore.HaveCScript(CScriptID(CScript() << OP_0 << vSolutions[0]))) {
+        if (sigversion == IsMineSigVersion::TOP && !keystore.HaveCScript(CScriptID(CScript() << OP_0 << vSolutions[0]))) {
             // We do not support bare witness outputs unless the P2SH version of it would be
             // acceptable as well. This protects against matching before segwit activates.
             // This also applies to the P2WSH case.
             break;
         }
-        isminetype ret = ::IsMine(keystore, GetScriptForDestination(CKeyID(uint160(vSolutions[0]))), isInvalid, SigVersion::WITNESS_V0);
+        isminetype ret = IsMineInner(keystore, GetScriptForDestination(CKeyID(uint160(vSolutions[0]))), isInvalid, IsMineSigVersion::WITNESS_V0);
         if (ret == ISMINE_SPENDABLE || ret == ISMINE_WATCH_SOLVABLE || (ret == ISMINE_NO && isInvalid))
             return ret;
         break;
     }
     case TX_PUBKEYHASH:
         keyID = CKeyID(uint160(vSolutions[0]));
-        if (sigversion != SigVersion::BASE) {
+        if (!PermitsUncompressed(sigversion)) {
             CPubKey pubkey;
             if (keystore.GetPubKey(keyID, pubkey) && !pubkey.IsCompressed()) {
                 isInvalid = true;
@@ -98,7 +100,7 @@ isminetype IsMine(const CKeyStore &keystore, const CScript& scriptPubKey, bool&
         CScriptID scriptID = CScriptID(uint160(vSolutions[0]));
         CScript subscript;
         if (keystore.GetCScript(scriptID, subscript)) {
-            isminetype ret = IsMine(keystore, subscript, isInvalid);
+            isminetype ret = IsMineInner(keystore, subscript, isInvalid, IsMineSigVersion::P2SH);
             if (ret == ISMINE_SPENDABLE || ret == ISMINE_WATCH_SOLVABLE || (ret == ISMINE_NO && isInvalid))
                 return ret;
         }
@@ -106,7 +108,7 @@ isminetype IsMine(const CKeyStore &keystore, const CScript& scriptPubKey, bool&
     }
     case TX_WITNESS_V0_SCRIPTHASH:
     {
-        if (!keystore.HaveCScript(CScriptID(CScript() << OP_0 << vSolutions[0]))) {
+        if (sigversion == IsMineSigVersion::TOP && !keystore.HaveCScript(CScriptID(CScript() << OP_0 << vSolutions[0]))) {
             break;
         }
         uint160 hash;
@@ -114,7 +116,7 @@ isminetype IsMine(const CKeyStore &keystore, const CScript& scriptPubKey, bool&
         CScriptID scriptID = CScriptID(hash);
         CScript subscript;
         if (keystore.GetCScript(scriptID, subscript)) {
-            isminetype ret = IsMine(keystore, subscript, isInvalid, SigVersion::WITNESS_V0);
+            isminetype ret = IsMineInner(keystore, subscript, isInvalid, IsMineSigVersion::WITNESS_V0);
             if (ret == ISMINE_SPENDABLE || ret == ISMINE_WATCH_SOLVABLE || (ret == ISMINE_NO && isInvalid))
                 return ret;
         }
@@ -123,13 +125,16 @@ isminetype IsMine(const CKeyStore &keystore, const CScript& scriptPubKey, bool&
 
     case TX_MULTISIG:
     {
+        // Never treat bare multisig outputs as ours (they can still be made watchonly-though)
+        if (sigversion == IsMineSigVersion::TOP) break;
+
         // Only consider transactions "mine" if we own ALL the
         // keys involved. Multi-signature transactions that are
         // partially owned (somebody else has a key that can spend
         // them) enable spend-out-from-under-you attacks, especially
         // in shared-wallet situations.
         std::vector<valtype> keys(vSolutions.begin()+1, vSolutions.begin()+vSolutions.size()-1);
-        if (sigversion != SigVersion::BASE) {
+        if (!PermitsUncompressed(sigversion)) {
             for (size_t i = 0; i < keys.size(); i++) {
                 if (keys[i].size() != 33) {
                     isInvalid = true;
@@ -150,3 +155,22 @@ isminetype IsMine(const CKeyStore &keystore, const CScript& scriptPubKey, bool&
     }
     return ISMINE_NO;
 }
+
+} // namespace
+
+isminetype IsMine(const CKeyStore& keystore, const CScript& scriptPubKey, bool& isInvalid)
+{
+    return IsMineInner(keystore, scriptPubKey, isInvalid, IsMineSigVersion::TOP);
+}
+
+isminetype IsMine(const CKeyStore& keystore, const CScript& scriptPubKey)
+{
+    bool isInvalid = false;
+    return IsMine(keystore, scriptPubKey, isInvalid);
+}
+
+isminetype IsMine(const CKeyStore& keystore, const CTxDestination& dest)
+{
+    CScript script = GetScriptForDestination(dest);
+    return IsMine(keystore, script);
+}
diff --git a/src/script/ismine.h b/src/script/ismine.h
index f93a66e35a..8573bdfbd2 100644
--- a/src/script/ismine.h
+++ b/src/script/ismine.h
@@ -33,9 +33,8 @@ typedef uint8_t isminefilter;
  * different SIGVERSION may have different network rules. Currently the only use of isInvalid is indicate uncompressed
  * keys in SigVersion::WITNESS_V0 script, but could also be used in similar cases in the future
  */
-isminetype IsMine(const CKeyStore& keystore, const CScript& scriptPubKey, bool& isInvalid, SigVersion = SigVersion::BASE);
-isminetype IsMine(const CKeyStore& keystore, const CScript& scriptPubKey, SigVersion = SigVersion::BASE);
-isminetype IsMine(const CKeyStore& keystore, const CTxDestination& dest, bool& isInvalid, SigVersion = SigVersion::BASE);
-isminetype IsMine(const CKeyStore& keystore, const CTxDestination& dest, SigVersion = SigVersion::BASE);
+isminetype IsMine(const CKeyStore& keystore, const CScript& scriptPubKey, bool& isInvalid);
+isminetype IsMine(const CKeyStore& keystore, const CScript& scriptPubKey);
+isminetype IsMine(const CKeyStore& keystore, const CTxDestination& dest);
 
 #endif // BITCOIN_SCRIPT_ISMINE_H
diff --git a/src/script/standard.h b/src/script/standard.h
index 3b2838a5bb..4922b7236b 100644
--- a/src/script/standard.h
+++ b/src/script/standard.h
@@ -23,7 +23,7 @@ class CScriptID : public uint160
 {
 public:
     CScriptID() : uint160() {}
-    CScriptID(const CScript& in);
+    explicit CScriptID(const CScript& in);
     CScriptID(const uint160& in) : uint160(in) {}
 };