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Bug #15934

closed

String#b can lead to memory corruption

Added by alanwu (Alan Wu) almost 3 years ago. Updated over 2 years ago.

Status:
Closed
Priority:
Normal
Assignee:
-
Target version:
-
ruby -v:
trunk(801d0d9), 2.4.6, 2.5.5, 2.6.3
[ruby-core:93207]

Description

The following script triggers use-after-free on trunk(801d0d9), 2.4.6, 2.5.5
and 2.6.3.

a = ('j' * 24).b.b
eval('', binding, a)

p a
4.times { GC.start }
p a

The consequence is usually that a gets corrupted (it depends on what the system allocator does when it frees memory). Here is a sample output for the script:

$> ruby -v bad.rb
ruby 2.6.3p62 (2019-04-16 revision 67580) [x86_64-darwin18]
"jjjjjjjjjjjjjjjjjjjjjjjj"
"D[D'\xFD\a\x00\xF0\x00\x00\x00\x00\x00\x00\x00\x90\x18\x00jjjjjj"

This is caused by the same underlying issue as #15792. Credits to wanabe-san for using eval as a cross-version way of registering a fstring.

I have a fix for this: https://github.com/ruby/ruby/pull/2183

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