Re: [PATCH] obexd: Fix null pointer dereference.

Johan Hedberg
2017-06-21T09:41:48Z

Hi Matias,

On Wed, Jun 21, 2017, Matias Karhumaa wrote:
> By sending OPP Put request before CONNECT we were able to cause
> SIGSEGV in obexd. Crash was caused by null pointer dereference.
>
> gdb output:
>
> Program received signal SIGSEGV, Segmentation fault.
> manager_request_authorization (transfer=transfer@entry=0x0, new_folder=new_folder@entry=0x7fffffffda18, new_name=new_name@entry=0x7fffffffda20) at obexd/src/manager.c:677
> 677 struct obex_session *os = transfer->session;
> (gdb) bt
> *#0 manager_request_authorization (transfer=transfer@entry=0x0, new_folder=new_folder@entry=0x7fffffffda18, new_name=new_name@entry=0x7fffffffda20) at obexd/src/manager.c:677
> *#1 0x000000000041b7a5 in opp_chkput (os=0x67de60, user_data=0x0) at obexd/plugins/opp.c:80
> *#2 0x0000000000426cc5 in check_put (obex=0x678a50, req=0x679250, user_data=0x67de60) at obexd/src/obex.c:831
> *#3 cmd_put (obex=0x678a50, req=0x679250, user_data=0x67de60) at obexd/src/obex.c:887
> *#4 0x00000000004145e7 in handle_request (req=0x679250, obex=0x678a50) at gobex/gobex.c:1199
> *#5 incoming_data (io=<optimized out>, cond=<optimized out>, user_data=0x678a50) at gobex/gobex.c:1375
> *#6 0x00007ffff749204a in g_main_dispatch (context=0x674810) at /build/glib2.0-prJhLS/glib2.0-2.48.2/./glib/gmain.c:3154
> *#7 g_main_context_dispatch (context=context@entry=0x674810) at /build/glib2.0-prJhLS/glib2.0-2.48.2/./glib/gmain.c:3769
> *#8 0x00007ffff74923f0 in g_main_context_iterate (context=0x674810, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>)
> at /build/glib2.0-prJhLS/glib2.0-2.48.2/./glib/gmain.c:3840
> *#9 0x00007ffff7492712 in g_main_loop_run (loop=0x66fdf0) at /build/glib2.0-prJhLS/glib2.0-2.48.2/./glib/gmain.c:4034
> *#10 0x000000000040dd0f in main (argc=1, argv=0x7fffffffde08) at obexd/src/main.c:322
>
> Crash was found using Synopsys Defensics Obex Server test suite.
> ---
> obexd/src/obex.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/obexd/src/obex.c b/obexd/src/obex.c
> index 788bffc..91fa838 100644
> --- a/obexd/src/obex.c
> +++ b/obexd/src/obex.c
> @@ -825,7 +825,7 @@ static gboolean check_put(GObex *obex, GObexPacket *req, void *user_data)
> struct obex_session *os = user_data;
> int ret;
>
> - if (os->service->chkput == NULL)
> + if (os->service->chkput == NULL || os->service_data == NULL)
> goto done;

As far as I understand, os->service_data is the OBEX service-specific
context, which I think can in principle validly be NULL. Also, isn't it
so that OBEX Object Push permits PUT without a preceding CONNECT (at
least that's what I remember from the times I was working with OBEX)?

It seems to me that the bug is with opp.c passing the service_data to
manager_request_authorization(), and service_data is expected to be the
obex_transfer object. However, currently the code creates this object
only upon CONNECT (in opp_connect).

I think one possible way to solve this would be to trigger a call to
os->service->connect if CONNECT hasn't been explicitly issued, however
then the code needs to track this in some other way since service_data
seems too unreliable.

Johan