Re: Use-after-free race condition,in OpenSSL's read buffer

[Solar Designer <solar () openwall com>]

On Sat, Apr 12, 2014 at 09:47:49PM -0600, Scotty Bauer wrote:
> Patch is available at:
> http://ftp.openbsd.org/pub/OpenBSD/patches/5.4/common/008_openssl.patch

Some context to this:

http://www.tedunangst.com/flak/post/analysis-of-openssl-freelist-reuse

This specific patch is found in Benson Kwok's bug report:

https://rt.openssl.org/Ticket/Display.html?id=2167&user=guest&pass=guest

Benson writes:

"The issue is when the buffer is released by ssl3_release_read_buffer(),
there may still be data left in the buffer (s->s3->rbuf.left != 0). With
single threading, when another read occurs, the same buffer is reused
during a call to ssl3_setup_read_buffer() so the data is still there and
can be read and processed so it works fine. When running with multiple
threads, the buffer is shared in a pool and another thread may have gotten
that buffer already. If the call to ssl3_setup_read_buffer() returns a new
buffer, it assume the data is still there but will run into parsing error
with the record."

(Of course, "parsing error" isn't necessarily the worst outcome.)

Alexander