Bug #12292: Race between OpenSSL::SSL::SSLSocket#stop and #connect can cause a segmentation fault

• Status: Closed
• Assignee: rhenium (Kazuki Yamaguchi)
• Target version: -
• ruby -v: ruby 2.4.0dev (2016-04-15 trunk 54594) [x86_64-linux]
• Backport: 2.1: WONTFIX, 2.2: REQUIRED, 2.3: DONE

[rhenium (Kazuki Yamaguchi)]

The following code will demonstrate the issue:

require "openssl"
require "socket"

ctx = OpenSSL::SSL::SSLContext.new
ctx.ciphers = "aNULL"

sock1, sock2 = UNIXSocket.pair
ssl1 = OpenSSL::SSL::SSLSocket.new(sock1, ctx)
ssl2 = OpenSSL::SSL::SSLSocket.new(sock2, ctx)

t = Thread.new { ssl1.connect } # => segmentation fault
ssl2.accept

ssl1.close # calls #stop (private method)
sock1.close

t.value

The SSL (OpenSSL land object) can be freed by SSLSocket#stop (#close) while SSLSocket#connect is still using it. This happens because SSLSocket#connect releases GVL while waiting for the peer.

There are two ways to resolve this:

• Check that the SSL object is still set every time after reacquiring GVL
• Change SSLSocket#stop not to free the SSL object

The latter introduces an incompatibility (#stop is currently documented as "prepares it for another connection").
I however prefer this because similar bugs can be introduced in future if we choose an ad-hoc way, and I don't think anyone reuses the SSLSocket object (keep in mind that we don't have interface to replace the underlying IO object).

Anyway I attach fixes in both way.

• 0001-ext-openssl-check-that-the-SSL-object-is-still-set-a.patch: the fix in the first way
• 0001-ext-openssl-make-OpenSSL-SSL-SSLSocket-non-reusable.patch: the fix in the second way
• 0002-ext-openssl-some-trivial-cleanups.patch: some minor cleanups, not actually related to this issue (what's the most desirable way to submit such trivial patches?)

[shyouhei (Shyouhei Urabe)]

• Status changed from Open to Assigned
• Assignee set to rhenium (Kazuki Yamaguchi)

Kazuki, I think it's OK for you to fix a segmentation fault now.

• Status changed from Assigned to Closed

Applied in changeset r55100.

---

openssl: fix possible SEGV on race between SSLSocket#stop and #connect

• ext/openssl/ossl_ssl.c (ossl_ssl_stop): Don't free the SSL struct
  here. Since some methods such as SSLSocket#connect releases GVL,
  there is a chance of use after free if we free the SSL from another
  thread. SSLSocket#stop was documented as "prepares it for another
  connection" so this is a slightly incompatible change. However when
  this sentence was added (r30090, Add toplevel documentation for
  OpenSSL, 2010-12-06), it didn't actually. The current behavior is
  from r40304 (Correct shutdown behavior w.r.t GC., 2013-04-15).
  [ruby-core:74978] [Bug #12292]

• ext/openssl/lib/openssl/ssl.rb (sysclose): Update doc.

• test/openssl/test_ssl.rb: Test this.

[usa (Usaku NAKAMURA)]

• Backport changed from 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN to 2.1: WONTFIX, 2.2: REQUIRED, 2.3: REQUIRED

[nagachika (Tomoyuki Chikanaga)]

• Backport changed from 2.1: WONTFIX, 2.2: REQUIRED, 2.3: REQUIRED to 2.1: WONTFIX, 2.2: REQUIRED, 2.3: DONE

ruby_2_3 r55866 merged revision(s) 55100.

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