From d6c892fe7b0c28d3b994323bdb690257d16b332e Mon Sep 17 00:00:00 2001
From: Damian Gryski <damian@gryski.com>
Date: Tue, 7 Dec 2021 22:31:07 -0800
Subject: [PATCH] src/runtime: fix nil map dereference

Operations on nil maps are accepted and shouldn't
panic. The base hashmapGet/hashmapDelete handled
nil-maps correctly, but the hashmapBinary versions
could segfault accessing the nil map while trying
to hash the key.

Fixes #2341
---
 src/runtime/hashmap.go | 8 ++++++++
 testdata/map.go        | 4 ++++
 testdata/map.txt       | 1 +
 3 files changed, 13 insertions(+)

diff --git a/src/runtime/hashmap.go b/src/runtime/hashmap.go
index 07d46b57..5c66e19e 100644
--- a/src/runtime/hashmap.go
+++ b/src/runtime/hashmap.go
@@ -307,16 +307,24 @@ func hashmapNext(m *hashmap, it *hashmapIterator, key, value unsafe.Pointer) boo
 // Hashmap with plain binary data keys (not containing strings etc.).
 
 func hashmapBinarySet(m *hashmap, key, value unsafe.Pointer) {
+	// TODO: detect nil map here and throw a better panic message?
 	hash := hashmapHash(key, uintptr(m.keySize))
 	hashmapSet(m, key, value, hash, memequal)
 }
 
 func hashmapBinaryGet(m *hashmap, key, value unsafe.Pointer, valueSize uintptr) bool {
+	if m == nil {
+		memzero(value, uintptr(valueSize))
+		return false
+	}
 	hash := hashmapHash(key, uintptr(m.keySize))
 	return hashmapGet(m, key, value, valueSize, hash, memequal)
 }
 
 func hashmapBinaryDelete(m *hashmap, key unsafe.Pointer) {
+	if m == nil {
+		return
+	}
 	hash := hashmapHash(key, uintptr(m.keySize))
 	hashmapDelete(m, key, hash, memequal)
 }
diff --git a/testdata/map.go b/testdata/map.go
index 4ca456ea..7d9ee6ae 100644
--- a/testdata/map.go
+++ b/testdata/map.go
@@ -57,6 +57,10 @@ func main() {
 		println(k) // unreachable
 	}
 
+	var nilbinmap map[uint16]int
+	delete(nilbinmap, 4)
+	println("nilbinmap:", nilbinmap[5])
+
 	arrKey := ArrayKey([4]byte{4, 3, 2, 1})
 	println(testMapArrayKey[arrKey])
 	testMapArrayKey[arrKey] = 5555
diff --git a/testdata/map.txt b/testdata/map.txt
index 834dd7ad..366f6467 100644
--- a/testdata/map.txt
+++ b/testdata/map.txt
@@ -53,6 +53,7 @@ true false 0
 nilmap: 0
 4
 42
+nilbinmap: 0
 4321
 5555
 itfMap[3]: 0