From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49550) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Wkfx7-0002Rv-P0 for qemu-devel@nongnu.org; Wed, 14 May 2014 16:39:07 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Wkfx2-0005YQ-AO for qemu-devel@nongnu.org; Wed, 14 May 2014 16:39:01 -0400 Sender: fluxion Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable From: Michael Roth In-Reply-To: <20140514142516.20269803@redhat.com> References: <1399473780-20374-1-git-send-email-marcel.a@redhat.com> <1399473780-20374-3-git-send-email-marcel.a@redhat.com> <53725800.3030404@suse.de> <53726D96.8030404@redhat.com> <5373A11E.90005@suse.de> <1400088577.14303.45.camel@localhost.localdomain> <20140514142516.20269803@redhat.com> Message-ID: <20140514203849.3192.91896@loki> Date: Wed, 14 May 2014 15:38:49 -0500 Subject: Re: [Qemu-devel] [PATCH 2/4] qapi: output visitor crashes qemu if it encounters a NULL value List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Luiz Capitulino , Marcel Apfelbaum Cc: mst@redhat.com, aik@ozlabs.ru, qemu-devel@nongnu.org, armbru@redhat.com, blauwirbel@gmail.com, jcmvbkbc@gmail.com, edgar.iglesias@gmail.com, gxt@mprc.pku.edu.cn, peter.chubb@nicta.com.au, proljc@gmail.com, agraf@suse.de, scottwood@freescale.com, borntraeger@de.ibm.com, hpoussin@reactos.org, aliguori@amazon.com, lersek@redhat.com, chouteau@adacore.com, jan.kiszka@web.de, stefanha@redhat.com, cornelia.huck@de.ibm.com, peter.crosthwaite@xilinx.com, mark.langsdorf@calxeda.com, michael@walle.cc, qemu-ppc@nongnu.org, pbonzini@redhat.com, =?utf-8?q?Andreas_F=C3=A4rber?= , aurelien@aurel32.net Quoting Luiz Capitulino (2014-05-14 13:25:16) > On Wed, 14 May 2014 20:29:37 +0300 > Marcel Apfelbaum wrote: > = > > On Wed, 2014-05-14 at 19:00 +0200, Andreas F=C3=A4rber wrote: > > > Am 13.05.2014 21:08, schrieb Eric Blake: > > > > On 05/13/2014 11:36 AM, Andreas F=C3=A4rber wrote: > > > >> Am 07.05.2014 16:42, schrieb Marcel Apfelbaum: > > > >>> A NULL value is not added to visitor's stack, but there is no > > > >>> check for that when the visitor tries to return that value, > > > >>> leading to Qemu crash. > > > >>> = > > > >>> Reviewed-by: Eric Blake Signed-off-by: > > > >>> Marcel Apfelbaum > > > >> = > > > >> Where does the Rb come from on this v1? Is it in any tree > > > >> already? > > > >> = > > > > = > > > > The (weak) R-b was here: = > > > > https://lists.gnu.org/archive/html/qemu-devel/2014-02/msg02861.html > > > = > > > Thanks. > > > > = > > > So Luiz was okay with it too, but his last message seems to be > > > indicating this needs to be fixed somewhere else, too: > > > = > > > https://lists.gnu.org/archive/html/qemu-devel/2014-02/msg05228.html > > > https://lists.gnu.org/archive/html/qemu-devel/2014-03/msg00217.html > > > = > > > Can/should that be addressed as a follow-up? Or is there a test case > > > that breaks? > > Simple and "popular" test case: the user does not use the -kernel-cmdli= ne parameter. > > The patch is needed because otherwise the main function will fail > > if no value is passed by the user to string parameters. = > > = > > Regarding Luiz's concern, it can be a follow-up as I am not aware of > > any problem with that. > = > My concern was that I wasn't sure if this is the right fix for the issue > or if it's papering over the real bug. I quickly checked the code and it > seemed to make sense, but I didn't have time to study it deeper. Not sure the fix is bad or not, but the cause might be a little more subtle than NULL string values as mentioned in the other thread. QmpOutputVisitor encodes NULL strings as "" via qmp_output_type_str(), so the problem doesn't seem to lie there: it shouldn't generate NULL values on the stack. I think the real issue is that object_property_get_str() actually calls an accessor via property_get_str to get the string, then explicitly *skips* the call to visit_type_str() if it is NULL (as it would be in the case of, say, kernel_cmdline option being NULL). So I wonder if maybe the real issue we're fixing is a corner case where you call qmp_output_get_qobject() on an "empty" QmpOutputVisitor. Surprised that's not covered by tests, but didn't see any coverage doing a cursory glance. Actually, might as well just add one.. diff --git a/tests/test-qmp-output-visitor.c b/tests/test-qmp-output-visito= r.c index e073d83..f190eaa 100644 --- a/tests/test-qmp-output-visitor.c +++ b/tests/test-qmp-output-visitor.c @@ -434,6 +434,17 @@ static void test_visitor_out_union(TestOutputVisitorDa= ta *data, QDECREF(qdict); } = +static void test_visitor_out_empty(TestOutputVisitorData *data, + const void *unused) +{ + QObject *arg; + QDict *qdict; + + arg =3D qmp_output_get_qobject(data->qov); + qdict =3D qobject_to_qdict(arg); + QDECREF(qdict); +} + static void init_native_list(UserDefNativeListUnion *cvalue) { int i; @@ -782,6 +793,8 @@ int main(int argc, char **argv) &out_visitor_data, test_visitor_out_list_qapi_= free); output_visitor_test_add("/visitor/output/union", &out_visitor_data, test_visitor_out_union); + output_visitor_test_add("/visitor/output/empty", + &out_visitor_data, test_visitor_out_empty); output_visitor_test_add("/visitor/output/native_list/int", &out_visitor_data, test_visitor_out_native_lis= t_int); output_visitor_test_add("/visitor/output/native_list/int8", mdroth@loki:~/w/qemu-build$ tests/test-qmp-output-visitor = /visitor/output/int: OK /visitor/output/bool: OK /visitor/output/number: OK /visitor/output/string: OK /visitor/output/no-string: OK /visitor/output/enum: OK /visitor/output/enum-errors: OK /visitor/output/struct: OK /visitor/output/struct-nested: OK /visitor/output/struct-errors: OK /visitor/output/list: OK /visitor/output/list-qapi-free: OK /visitor/output/union: OK /visitor/output/empty: Segmentation fault (core dumped) So I guess the question is whether we should support converting an empty QmpOutputVisitor to a QObject. I would say yes, and that a NULL value is probably the most reasonable value. I would ask that commit/code is a little more explicit about what corner ca= se is being handled though, and that something like the above unit test be included with the series. > = > We could ask Michael Roth or Anthony, but I wouldn't hold this series > because of that. Here's my ACK if you need it: > = > Acked-by: Luiz Capitulino