[Bug 1940656] Re: Potential use after free bugs in 1.1.1

[Dimitri John Ledkov]

I would agree that any hypothetical use-after-free / double-free errors
are usually also security vulnerabilities. But these ones were
discovered with static analysis and/or affecting engine use, in error
conditions only. Thus connectivity must already be failing / denied,
before one can trip these ones up. Not sure if one can further stage an
attack by staging a connection failure, and try to disclose information
from that.

Will ping security team about it.

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https://bugs.launchpad.net/bugs/1940656

Title:
  Potential use after free bugs in 1.1.1

Status in openssl package in Ubuntu:
  Fix Released
Status in openssl source package in Focal:
  In Progress

Bug description:
  [Impact]

   * There have been multiple use-after-free bugs fixed in OpenSSL 1.1.1
  stable branches which have not yet been applied in Focal. They are
  difficult to reproduce, often require an engine to be used, and
  somehow fail, as these use-after-free bugs are all in error conditions
  and error paths. Usually fixing local configuration, and making engine
  available is the right solution. It is however better to return errors
  than crash. These patches are in 1.1.1h+ and openssl-3.

  [Test Plan]

   * The fixes were applied upstream without clear reproducers, or unit
  tests

   * Check that all autopkgtests pass and there no regressions

   * Configure and use openssl with any engine and ensure that it
  continues to work

  [Where problems could occur]

   * There will be behaviour change, such that multithreaded
  applications may now notice Null pointers from the openssl engine
  apis, when previously they saw valid pointers which were freed
  already. Meaning that on connection failures, daemon or application
  shutdowns, different messages might be generated i.e. invalid engine
  context, unallocated methods, instead of crashing with double free.

  [Other Info]

   * Multiple customers are using openssl 1.1.1 with engines these days,
  reporting various issues, it is better to have more resilient openssl
  w.r.t. engine use in case of engine missuse.

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