This went to openssl-users but just to be sure...
--
[Eric Rescorla [EMAIL PROTECTED]]
http://www.rtfm.com/
"Andy Schneider" <[EMAIL PROTECTED]> writes:
> It looks like although it has the right data and probably the right
> frame (since it gets the MAC correctly) the client is in some state
> where it isn't using the correct data to compute the MAC. Anyone any
> hints as to why this maybe?
[...lots of discussion deleted...]
I can't exactly replicate the behavior you're seeing. I
seem to be able to do an arbitrary number of SSL_reads()
interlaced with a rehandshake. Writes, however, are a different
matter. If I try to write interlaced with a rehandshake
I get MAC errors right away.
After some investigation, the problem appears to be that
you can't safely interlace SSL_write() with rehandshakes.
Consider the following sequence of events:
CLIENT SERVER
SSL_renegotiate();
SSL_do_handshake();
calls ssl_init_wbio_buffer()
sends HelloRequest
SSL_read()
read the HelloRequest and
start the handshake,
sending the ClientHello
SSL_write()
this write gets buffered.
SSL_read();
Now, when SSL_read() reads the ClientHello it eventually calls
ssl3_accept() which calls ssl_init_wbio_buffer AGAIN. This causes
the buffer to be zeroed with the result that the record from
the SSL_write() gets lost. Then when the ServerHello is transmitted
the client tries to decrypt it with the wrong CBC residue (or the
wrong part of RC4 keystream) and the wrong sequence #. This causes
MAC errors. This is a bug in OpenSSL.
The quick and dirty fix seems to be is to change ssl_init_wbio_buffer
by adding a BIO_flush() (see below). There may be something cleaner,
though. I don't immediately see how this fix can do any harm,
but there may well be somethign unobvious that I'm missing.
int ssl_init_wbio_buffer(SSL *s,int push)
{
BIO *bbio;
if (s->bbio == NULL)
{
bbio=BIO_new(BIO_f_buffer());
if (bbio == NULL) return(0);
s->bbio=bbio;
}
else
{
bbio=s->bbio;
EKR: ---> (void)BIO_flush(bbio);
if (s->bbio == s->wbio)
s->wbio=BIO_pop(s->wbio);
}
(void)BIO_reset(bbio);
/* if (!BIO_set_write_buffer_size(bbio,16*1024)) */
if (!BIO_set_read_buffer_size(bbio,1))
{
SSLerr(SSL_F_SSL_INIT_WBIO_BUFFER,ERR_R_BUF_LIB);
return(0);
}
if (push)
{
if (s->wbio != bbio)
s->wbio=BIO_push(bbio,s->wbio);
}
else
{
if (s->wbio == bbio)
s->wbio=BIO_pop(bbio);
}
return(1);
}
Andy, let me know if this patch fixes your problem. It fixes mine :)
-Ekr
P.S. Does OpenSSL have some official way to report bugs?
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