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Subject: Re: [libssh2] Crash while Key Exchange at libssh2 session startup time!!

Re: [libssh2] Crash while Key Exchange at libssh2 session startup time!!

From: Satish Mittal <satish.mittal_at_gmail.com>
Date: Wed, 8 Nov 2006 20:04:26 +0530

Yes, we need to add all these checks, and probably more, to catch the
read/write status wherever we are calling them. But these will just fail the
sftp init, instead of crashing the application.

That doesn't solve my problem, since my sftp client application succeeds
against the very same sftp server against which it fails. I would want it to
succeed always, or fail always.

Thanks,
Satish

On 11/8/06, James Housley <jim_at_thehousleys.net> wrote:
>
> On Nov 7, 2006, at 6:22 PM, Chris Nystrom wrote:
>
> > On 11/7/06, Satish Mittal <satish.mittal_at_gmail.com> wrote:
> >> Dear All,
> >>
> >> I am using libssh2-0.14 on windows. From my application, when i call
> >> libssh2_session_startup(), my application is randomly (but very
> >> frequently)
> >> crashing, reporting 'out of virtual memory'.
> >>
> >> The problem is during the DH key exchange phase, when the call to
> >> libssh2_packet_read() is made,
> >>
> >> long buf_len, payload_len; //line 876
> >> unsigned long packet_length;
> >> unsigned long padding_length;
> >>
> >> if (should_block) {
> >> buf_len = libssh2_blocking_read(session, buf, 5);
>
> This should also have a check of the return value for the same reasons.
>
> tmpvar = libssh2_blocking_read(session, buf, 5 -
> buf_len);
>
> if (tmpvar < 0) {
> /* something bad happened */
> return(-1);
> }
> buf_len = tmpvar;
>
>
> >> } else {
> >> buf_len = recv(session->socket_fd, buf, 1,
> >> LIBSSH2_SOCKET_RECV_FLAGS(session));
> >> if (buf_len <= 0) {
> >> return 0;
> >> }
> >> buf_len += libssh2_blocking_read(session, buf, 5 -
> >> buf_len);
> >> //line 887
> >
> > How about replacing the above line with something like:
> >
> > tmpvar = libssh2_blocking_read(session, buf, 5 -
> > buf_len);
> >
> > if (tmpvar < 0) {
> > /* something bad happened */
> > return(-1);
> > }
> >
> > buf_len += tmpvar;
> >
> > It does no good for functions to provide error codes if you do not
> > check for them. :)
> >
> >> }
> >> if (buf_len < 5) {
> >> /* Something bad happened */
> >> return -1; //line 891
> >> }
> >> packet_length = libssh2_ntohu32(buf); //line893
> >> padding_length = buf[4];
> >> #ifdef LIBSSH2_DEBUG_TRANSPORT
> >> _libssh2_debug(session, LIBSSH2_DBG_TRANS, "Processing
> >> plaintext packet
> >> %lu bytes long (with %lu bytes padding)", packet_length,
> >> padding_length);
> >> #endif
> >>
> >> payload_len = packet_length - padding_length - 1; /*
> >> padding_length(1) */ //line 899
> >> payload = LIBSSH2_ALLOC(session, payload_len);
> >>
> >> Here payload_len is coming out to be a huge number (junk value on
> >> stack)
> >> since packet_length in line 893 is junk. This is in turn because
> >> in line
> >> 887, the libssh2_blocking_read() returns -1. But since buf_len is
> >> declared
> >> as an unsigned long, so -1 gets converted to a huge 32bit value,
> >> which then
> >> eventually crashes the application.
> >>
> >> I have tried editing line 876 to declare buf_len and payload_len
> >> as long,
> >> instead of unsigned long. This then in turn returns -1 in line 891
> >> and fails
> >> the libssh2_session_startup() call.
> >
>
> Jim
>
> --
>
> /"\ ASCII Ribbon Campaign .
> \ / - NO HTML/RTF in e-mail .
> X - NO Word docs in e-mail .
> / \ -----------------------------------------------------------------
> jeh@FreeBSD.org http://www.FreeBSD.org The Power to Serve
> jim@TheHousleys.Net http://www.TheHousleys.net
> ---------------------------------------------------------------------
> Do not meddle in the affairs of dragons, for you are crunchy and taste
> good with ketchup.
>
>
>

-- 
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Received on 2006-11-08

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