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

[Luiz Augusto von Dentz <luiz.dentz@gmail.com>]

Hi Johan,

On Wed, Jun 21, 2017 at 12:41 PM, Johan Hedberg <johan.hedberg@gmail.com> wrote:
> 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)?

Yep, OPP can start a transfer without a CONNECT so the service_data
will need to be instantiated directly on PUT if that wasn't created
yet.

> 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
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-- 
Luiz Augusto von Dentz