fix: Check trustline limits for share-denominated vault withdrawals (#6645)

src/libxrpl/tx/transactors/vault/VaultWithdraw.cpp

@@ -43,10 +43,10 @@ VaultWithdraw::preclaim(PreclaimContext const& ctx)
     if (!vault)
         return tecNO_ENTRY;
 
-    auto const assets = ctx.tx[sfAmount];
+    auto const amount = ctx.tx[sfAmount];
     auto const vaultAsset = vault->at(sfAsset);
     auto const vaultShare = vault->at(sfShareMPTID);
-    if (assets.asset() != vaultAsset && assets.asset() != vaultShare)
+    if (amount.asset() != vaultAsset && amount.asset() != vaultShare)
         return tecWRONG_ASSET;
 
     auto const& vaultAccount = vault->at(sfAccount);
@@ -67,8 +67,53 @@ VaultWithdraw::preclaim(PreclaimContext const& ctx)
         // LCOV_EXCL_STOP
     }
 
-    if (auto const ret = canWithdraw(ctx.view, ctx.tx))
-        return ret;
+    if (ctx.view.rules().enabled(fixSecurity3_1_3) && amount.asset() == vaultShare)
+    {
+        // Post-fixSecurity3_1_3: if the user specified shares, convert
+        // to the equivalent asset amount before checking withdrawal
+        // limits. Pre-amendment the limit check was skipped for
+        // share-denominated withdrawals.
+        auto const sleIssuance = ctx.view.read(keylet::mptIssuance(vaultShare));
+        if (!sleIssuance)
+        {
+            // LCOV_EXCL_START
+            JLOG(ctx.j.error()) << "VaultWithdraw: missing issuance of vault shares.";
+            return tefINTERNAL;
+            // LCOV_EXCL_STOP
+        }
+
+        try
+        {
+            auto const maybeAssets = sharesToAssetsWithdraw(vault, sleIssuance, amount);
+            if (!maybeAssets)
+                return tefINTERNAL;  // LCOV_EXCL_LINE
+
+            if (auto const ret = canWithdraw(
+                    ctx.view,
+                    account,
+                    dstAcct,
+                    *maybeAssets,
+                    ctx.tx.isFieldPresent(sfDestinationTag)))
+                return ret;
+        }
+        catch (std::overflow_error const&)
+        {
+            // It's easy to hit this exception from Number with large enough Scale
+            // so we avoid spamming the log and only use debug here.
+            JLOG(ctx.j.debug())  //
+                << "VaultWithdraw: overflow error with"
+                << " scale=" << (int)vault->at(sfScale)  //
+                << ", assetsTotal=" << vault->at(sfAssetsTotal)
+                << ", sharesTotal=" << sleIssuance->at(sfOutstandingAmount)
+                << ", amount=" << amount.value();
+            return tecPATH_DRY;
+        }
+    }
+    else
+    {
+        if (auto const ret = canWithdraw(ctx.view, ctx.tx))
+            return ret;
+    }
 
     // If sending to Account (i.e. not a transfer), we will also create (only
     // if authorized) a trust line or MPToken as needed, in doApply().

src/test/app/Vault_test.cpp

@@ -5231,6 +5231,102 @@ class Vault_test : public beast::unit_test::suite
         }
     }
 
+    // Reproduction: canWithdraw IOU limit check bypassed when
+    // withdrawal amount is specified in shares (MPT) rather than in assets.
+    void
+    testBug6_LimitBypassWithShares()
+    {
+        using namespace test::jtx;
+        testcase("Bug6 - limit bypass with share-denominated withdrawal");
+
+        auto const allAmendments = testable_amendments() | featureSingleAssetVault;
+
+        for (auto const& features : {allAmendments, allAmendments - fixSecurity3_1_3})
+        {
+            bool const withFix = features[fixSecurity3_1_3];
+
+            Env env{*this, features};
+            Account const owner{"owner"};
+            Account const issuer{"issuer"};
+            Account const depositor{"depositor"};
+            Account const charlie{"charlie"};
+            Vault const vault{env};
+
+            env.fund(XRP(1000), issuer, owner, depositor, charlie);
+            env(fset(issuer, asfAllowTrustLineClawback));
+            env.close();
+
+            PrettyAsset const asset = issuer["IOU"];
+            env.trust(asset(1000), owner);
+            env.trust(asset(1000), depositor);
+            env(pay(issuer, owner, asset(200)));
+            env(pay(issuer, depositor, asset(200)));
+            env.close();
+
+            // Charlie gets a LOW trustline limit of 5
+            env.trust(asset(5), charlie);
+            env.close();
+
+            auto const [tx, keylet] = vault.create({.owner = owner, .asset = asset});
+            env(tx);
+            env.close();
+
+            auto const depositTx =
+                vault.deposit({.depositor = depositor, .id = keylet.key, .amount = asset(100)});
+            env(depositTx);
+            env.close();
+
+            // Get the share MPT info
+            auto const vaultSle = env.le(keylet);
+            if (!BEAST_EXPECT(vaultSle))
+                return;
+            auto const mptIssuanceID = vaultSle->at(sfShareMPTID);
+            MPTIssue const shares(mptIssuanceID);
+            PrettyAsset const share(shares);
+
+            // CONTROL: Withdraw 10 IOU (asset-denominated) to charlie.
+            // Charlie's limit is 5, so this should be rejected with tecNO_LINE
+            // regardless of the amendment.
+            {
+                auto withdrawTx =
+                    vault.withdraw({.depositor = depositor, .id = keylet.key, .amount = asset(10)});
+                withdrawTx[sfDestination] = charlie.human();
+                env(withdrawTx, ter{tecNO_LINE});
+                env.close();
+            }
+            auto const charlieBalanceBefore = env.balance(charlie, asset.raw().get<Issue>());
+
+            // Withdraw the equivalent amount in shares to charlie.
+            // Post-fix: rejected (tecNO_LINE) because the share amount is
+            //   converted to assets and the trustline limit is checked.
+            // Pre-fix: succeeds (tesSUCCESS) because the limit check was
+            //   skipped for share-denominated withdrawals.
+            {
+                auto withdrawTx = vault.withdraw(
+                    {.depositor = depositor,
+                     .id = keylet.key,
+                     .amount = STAmount(share, 10'000'000)});
+                withdrawTx[sfDestination] = charlie.human();
+                env(withdrawTx, ter{withFix ? TER{tecNO_LINE} : TER{tesSUCCESS}});
+                env.close();
+
+                auto const charlieBalanceAfter = env.balance(charlie, asset.raw().get<Issue>());
+                if (withFix)
+                {
+                    // Post-fix: charlie's balance is unchanged — the withdrawal
+                    // was correctly rejected despite being share-denominated.
+                    BEAST_EXPECT(charlieBalanceAfter == charlieBalanceBefore);
+                }
+                else
+                {
+                    // Pre-fix: charlie received the assets, bypassing the
+                    // trustline limit.
+                    BEAST_EXPECT(charlieBalanceAfter > charlieBalanceBefore);
+                }
+            }
+        }
+    }
+
 public:
     void
     run() override
@@ -5251,6 +5347,7 @@ public:
         testVaultClawbackBurnShares();
         testVaultClawbackAssets();
         testAssetsMaximum();
+        testBug6_LimitBypassWithShares();
     }
 };