From 09295ea796900fb7b05d29e93364090e21598566 Mon Sep 17 00:00:00 2001
From: Kasumi Hanazuki <kasumi@rollingapple.net>
Date: Sat, 25 Mar 2023 08:12:23 +0900
Subject: [PATCH] IO::Buffer#resize: Free internal buffer if new size is zero
 (#7569)

`#resize(0)` on an IO::Buffer with internal buffer allocated will
result in calling `realloc(data->base, 0)`. The behavior of `realloc`
with size = 0 is implementation-defined (glibc frees the object
and returns NULL, while BSDs return an inaccessible object). And
thus such usage is deprecated in standard C (upcoming C23 will make it
UB).

To avoid this problem, just `free`s the memory when the new size is zero.
---
 io_buffer.c                 |  5 +++++
 test/ruby/test_io_buffer.rb | 18 ++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/io_buffer.c b/io_buffer.c
index 91083cd7e4d3ab..1ff3935094f2a3 100644
--- a/io_buffer.c
+++ b/io_buffer.c
@@ -1422,6 +1422,11 @@ rb_io_buffer_resize(VALUE self, size_t size)
 #endif
 
     if (data->flags & RB_IO_BUFFER_INTERNAL) {
+        if (size == 0) {
+            io_buffer_free(data);
+            return;
+        }
+
         void *base = realloc(data->base, size);
 
         if (!base) {
diff --git a/test/ruby/test_io_buffer.rb b/test/ruby/test_io_buffer.rb
index 55e347471db125..e29400d76e6668 100644
--- a/test/ruby/test_io_buffer.rb
+++ b/test/ruby/test_io_buffer.rb
@@ -156,6 +156,24 @@ def test_resize_preserve
     assert_equal message, buffer.get_string(0, message.bytesize)
   end
 
+  def test_resize_zero_internal
+    buffer = IO::Buffer.new(1)
+
+    buffer.resize(0)
+    assert_equal 0, buffer.size
+
+    buffer.resize(1)
+    assert_equal 1, buffer.size
+  end
+
+  def test_resize_zero_external
+    buffer = IO::Buffer.for('1')
+
+    assert_raise IO::Buffer::AccessError do
+      buffer.resize(0)
+    end
+  end
+
   def test_compare_same_size
     buffer1 = IO::Buffer.new(1)
     assert_equal buffer1, buffer1