merge revision(s) 199b59f065ce6f1c13b8424f35a70c513523211b: [Backport #19116]

	Fix bug in array pack with shared strings

	If string literals are long and they become shared, we need to make them
	independent before we can write to them. [Bug #19116]
	---
	 pack.c                  | 1 +
	 test/ruby/test_array.rb | 6 ++++++
	 2 files changed, 7 insertions(+)

1 files changed, 3 insertions, 2 deletions

diff --git a/pack.c b/pack.c
index 1fbbd724d7..7de07a51d1 100644
--- a/pack.c
+++ b/pack.c
@@ -212,12 +212,13 @@ pack_pack(rb_execution_context_t *ec, VALUE ary, VALUE fmt, VALUE buffer)
     pend = p + RSTRING_LEN(fmt);
 
     if (NIL_P(buffer)) {
-	res = rb_str_buf_new(0);
+        res = rb_str_buf_new(0);
     }
     else {
         if (!RB_TYPE_P(buffer, T_STRING))
             rb_raise(rb_eTypeError, "buffer must be String, not %s", rb_obj_classname(buffer));
-	res = buffer;
+        rb_str_modify(buffer);
+        res = buffer;
     }
 
     idx = 0;