I recently started using libcurl and compiled it with MinGW.
I wanted to use the windows built-in certs so I opted for using WinSSL.
This combination crashes. Can easily be reproduced: just run curl.exe -g
https://google.com
The version info:
curl 7.30.0 (i686-pc-mingw32) libcurl/7.30.0 WinSSL zlib/1.2.7
Protocols: http https
Features: Debug TrackMemory GSS-Negotiate Largefile NTLM SSL SSPI libz

I started digging into the curl code to see if I could figure out the cause
and I somewhat did:
There is a problem in the Curl_schannel_shutdown function.
At curl_schannel.c:1146 it calls: Curl_ssl_getsessionid but at this point
the data->state.session
is not allocated.
This is because the shutdown comes from close_all_connections at
multi.c:1761
where they swap out the original SessionHandle (which does have
state.session allocated) with the multi->closure_handle.
The line can be found at multi.c:1767
The multi->closure_handle doesn't have the SessionHandle.state.session
allocated causing a
NULL pointer dereference.
I am not sure what the right fix is here because I only just started
looking into the code and the
multi interface is a little hard to understand.
First things that came to mind where:
Is the original SessionHandle ever freed after being swapped out? potential
memory leak?
Adding NULL checks in Curl_ssl_getsessionid will 'fix' the crash but it
might break the logic in Curl_schannel_shutdown because it expects to get
info from the 'real' SessionHandle struct?

A work around is to use --no-sessionid because Curl_ssl_getsessionid then
returns at the start.

Another note: I had link errors to the gdi32 lib when building curl with
MinGW.
So I had to make a modification at configure.am:1568 to put the gdi32 lib
behind the other libs:
LIBS="$LIBS -lgdi32"
I don't know if this is the right thing to do as I am new to MinGW,
autotools and GNU in general.

-------------------------------------------------------------------
List admin: http://cool.haxx.se/list/listinfo/curl-library
Etiquette: http://curl.haxx.se/mail/etiquette.html
Received on 2013-04-18