From d7603f72c1f8bbf62ce69d0e1d12decdd1463c40 Mon Sep 17 00:00:00 2001
From: Dirkjan Bussink <d.bussink@gmail.com>
Date: Thu, 3 Aug 2023 15:16:49 +0200
Subject: [PATCH] fastparse: Fix bug in overflow detection

When we have an overflow here, we didn't always correctly detect this
when we parse a value.

The switch trick here makes the compiler see the very common case of
base 10 (which we use most of the time by far) and turn the computation
into a constant value.

Signed-off-by: Dirkjan Bussink <d.bussink@gmail.com>
---
 go/mysql/fastparse/fastparse.go      | 28 ++++++++++++++++++++++++++++
 go/mysql/fastparse/fastparse_test.go | 12 ++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/go/mysql/fastparse/fastparse.go b/go/mysql/fastparse/fastparse.go
index 1296bf5866e..33aa16105c2 100644
--- a/go/mysql/fastparse/fastparse.go
+++ b/go/mysql/fastparse/fastparse.go
@@ -65,6 +65,18 @@ next:
 			break next
 		}
 
+		var cutoff uint64
+		switch base {
+		case 10:
+			cutoff = math.MaxUint64/10 + 1
+		case 16:
+			cutoff = math.MaxUint64/16 + 1
+		default:
+			cutoff = math.MaxUint64/uint64(base) + 1
+		}
+		if d >= cutoff {
+			return math.MaxUint64, fmt.Errorf("cannot parse uint64 from %q: %w", s, ErrOverflow)
+		}
 		v := d*uint64(base) + uint64(b)
 		if v < d {
 			return math.MaxUint64, fmt.Errorf("cannot parse uint64 from %q: %w", s, ErrOverflow)
@@ -139,6 +151,22 @@ next:
 			break next
 		}
 
+		var cutoff uint64
+		switch base {
+		case 10:
+			cutoff = math.MaxInt64/10 + 1
+		case 16:
+			cutoff = math.MaxInt64/16 + 1
+		default:
+			cutoff = math.MaxInt64/uint64(base) + 1
+		}
+		if d >= cutoff {
+			if minus {
+				return math.MinInt64, fmt.Errorf("cannot parse int64 from %q: %w", s, ErrOverflow)
+			}
+			return math.MaxInt64, fmt.Errorf("cannot parse int64 from %q: %w", s, ErrOverflow)
+		}
+
 		v := d*uint64(base) + uint64(b)
 		if v < d {
 			if minus {
diff --git a/go/mysql/fastparse/fastparse_test.go b/go/mysql/fastparse/fastparse_test.go
index f6477422459..bec312b0bb5 100644
--- a/go/mysql/fastparse/fastparse_test.go
+++ b/go/mysql/fastparse/fastparse_test.go
@@ -161,6 +161,12 @@ func TestParseInt64(t *testing.T) {
 			expected: 9223372036854775807,
 			err:      `cannot parse int64 from "18446744073709551616": overflow`,
 		},
+		{
+			input:    "31415926535897932384",
+			base:     10,
+			expected: 9223372036854775807,
+			err:      `cannot parse int64 from "31415926535897932384": overflow`,
+		},
 		{
 			input:    "1.1",
 			base:     10,
@@ -297,6 +303,12 @@ func TestParseUint64(t *testing.T) {
 			expected: 18446744073709551615,
 			err:      `cannot parse uint64 from "18446744073709551616": overflow`,
 		},
+		{
+			input:    "31415926535897932384",
+			base:     10,
+			expected: 18446744073709551615,
+			err:      `cannot parse uint64 from "31415926535897932384": overflow`,
+		},
 		{
 			input:    "1.1",
 			base:     10,