Function ssl2_read, formerly known as SSL2_read and (via a #define in
0.6.6b) also as SSL_read, in file ssl/s2_pkt.c contains the following
confusing code and comment:
/* If a 0 byte packet was sent, return 0, otherwise
* we play havoc with people using select with
* blocking sockets. Let them handle a packet at a time,
* they should really be using non-blocking sockets. */
if (s->s2->ract_data_length == 0)
return(0);
return(ssl2_read(s,buf,len));
I believe that this is now wrong, and alreay was wrong in 0.6.6b. Any
SSL_read or SSL_write can block even if select() signalled readability
or writeability -- the select() result means only that progress is
guaranteed, but not that the SSL_read or SSL_write will complete in
one call: For every SSL_read or SSL_write, the application program has
to expect several OS level reads and writes (in both directions as a
handshake can be started at any time), and if you really want to avoid
blocks, you must use non-blocking I/O. So I think what we should
really do is ignore the empty block and do a "goto" to the start of
the function (a recursive call to the function would be bad because if
someone has the bad luck to have to use a compiler that does not
recognize end recursion, an attacker can fill the stack).
Am I right?
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