Bug #19469: Crash when resizing generic iv list

• Status: Closed
• Assignee: -
• Target version: -
• Backport: 2.7: DONTNEED, 3.0: DONTNEED, 3.1: DONTNEED, 3.2: DONE

[peterzhu2118 (Peter Zhu)]

GitHub PR: https://github.com/ruby/ruby/pull/7407

The following script can sometimes trigger a crash:

GC.stress = true

class Array
  def foo(bool)
    if bool
      @a = 1
      @b = 2
      @c = 1
    else
      @c = 1
    end
  end
end

obj = []
obj.foo(true)

obj2 = []
obj2.foo(false)

obj3 = []
obj3.foo(true)

This is because vm_setivar_default calls rb_ensure_generic_iv_list_size to resize the iv list. However, the call to gen_ivtbl_resize reallocs the iv list, and then inserts into the generic iv table. If the st_insert triggers a GC then the old iv list will be read during marking, causing a use-after-free bug.

[alanwu (Alan Wu)]

Could this be the cause of #19433?
The stack traces seem to indicate generic IV table resizing.

[peterzhu2118 (Peter Zhu)]

• Status changed from Open to Closed

Applied in changeset git|62c2082f1f726cb90d8c332fbedbecf41d5d82ec.

---

[Bug #19469] Fix crash when resizing generic iv list

The following script can sometimes trigger a crash:

GC.stress = true

class Array
  def foo(bool)
    if bool
      @a = 1
      @b = 2
      @c = 1
    else
      @c = 1
    end
  end
end

obj = []
obj.foo(true)

obj2 = []
obj2.foo(false)

obj3 = []
obj3.foo(true)

This is because vm_setivar_default calls rb_ensure_generic_iv_list_size
to resize the iv list. However, the call to gen_ivtbl_resize reallocs
the iv list, and then inserts into the generic iv table. If the
st_insert triggers a GC then the old iv list will be read during
marking, causing a use-after-free bug.

Co-Authored-By: Jemma Issroff [e-mail]

[byroot (Jean Boussier)]

• Related to Bug #19477: segfault during GC if ivars set on arrays added

[peterzhu2118 (Peter Zhu)]

• Related to Bug #19433: Segmentation fault in 3.2.0/3.2.1 on M1 Mac added

[naruse (Yui NARUSE)]

• Backport changed from 2.7: DONTNEED, 3.0: DONTNEED, 3.1: DONTNEED, 3.2: REQUIRED to 2.7: DONTNEED, 3.0: DONTNEED, 3.1: DONTNEED, 3.2: DONE

ruby_3_2 f3abe5ba645839fb2a686aee18d3466b59256af0 merged revision(s) 0700d0fd1c77b4fddf803dea3c10be654df600ff,62c2082f1f726cb90d8c332fbedbecf41d5d82ec.