file.c: fix buffer overflow

* file.c (rb_readlink): fix buffer overflow on a long symlink. since
  rb_str_modify_expand() expands from its length but not its capacity,
  need to set the length properly for each expansion.
  [ruby-core:58592] [Bug #9157]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43853 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 1 insertions, 0 deletions

diff --git a/file.c b/file.c
index b14f42e1f8..77facacfcf 100644
--- a/file.c
+++ b/file.c
@@ -2618,6 +2618,7 @@ rb_readlink(VALUE path)
 	) {
 	rb_str_modify_expand(v, size);
 	size *= 2;
+	rb_str_set_len(v, size);
     }
     if (rv < 0) {
 	rb_str_resize(v, 0);