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Re: [libvirt] [PATCH 3/7] nwfilter_ebiptables_driver.c: avoid NULL dereference




Matthias Bolte <matthias bolte googlemail com> wrote on 04/14/2010 08:20:22 PM:


> "Daniel P. Berrange", libvir-list

>
> 2010/4/15 Stefan Berger <stefanb us ibm com>:
> >
> > libvir-list-bounces redhat com wrote on 04/14/2010 01:40:17 PM:
> >
> >
> >> Please respond to "Daniel P. Berrange"
> >>
> >> On Wed, Apr 14, 2010 at 06:02:32PM +0200, Jim Meyering wrote:
> >> > From: Jim Meyering <meyering redhat com>
> >> >
> >> > * src/nwfilter/nwfilter_ebiptables_driver.c (ebiptablesApplyNewRules):
> >> > Don't dereference a NULL or uninitialized pointer when given
> >> > an empty list of rules.  Add an sa_assert(inst) in each loop to
> >> > tell clang that the uses of "inst[i]" are valid.
> >> > ---
> >> >  src/nwfilter/nwfilter_ebiptables_driver.c |    8 +++++---
> >> >  1 files changed, 5 insertions(+), 3 deletions(-)
> >> >
> >> > diff --git a/src/nwfilter/nwfilter_ebiptables_driver.c b/src/
> >> nwfilter/nwfilter_ebiptables_driver.c
> >> > index b481b4c..f54099f 100644
> >> > --- a/src/nwfilter/nwfilter_ebiptables_driver.c
> >> > +++ b/src/nwfilter/nwfilter_ebiptables_driver.c
> >> > @@ -2834,11 +2834,11 @@ ebiptablesApplyNewRules(virConnectPtr conn
> >> ATTRIBUTE_UNUSED,
> >> >      bool haveIptables = false;
> >> >      bool haveIp6tables = false;
> >> >
> >> > -    if (inst)
> >> > -        qsort(inst, nruleInstances, sizeof(inst[0]),
> >> > -              ebiptablesRuleOrderSort);
> >> > +    if (nruleInstances > 1 && inst)
> >> > +        qsort(inst, nruleInstances, sizeof(inst[0]),
> >> ebiptablesRuleOrderSort);
> >> >
> >> >      for (i = 0; i < nruleInstances; i++) {
> >> > +        sa_assert (inst);
> >> >          if (inst[i]->ruleType == RT_EBTABLES) {
> >> >              if (inst[i]->chainprefix == CHAINPREFIX_HOST_IN_TEMP)
> >> >                  chains_in  |= (1 << inst[i]->neededProtocolChain);
> >> > @@ -2881,6 +2881,7 @@ ebiptablesApplyNewRules(virConnectPtr conn
> >> ATTRIBUTE_UNUSED,
> >> >          goto tear_down_tmpebchains;
> >> >
> >> >      for (i = 0; i < nruleInstances; i++)
> >> > +        sa_assert (inst);
> >
> >
> > Due to this statement here I get segmentation faults for which there is no
> > reason. I have no idea why that is but I have to deactivate this line for it
> > to work again.
> > The same is not true for the statement further above...  So strange.
> >
> >    Stefan
> >
>
> This one is obvious. The second for loop has no {} abound it's block.
> Before the addition of sa_assert the switch formed the block of the
> for loop and everything works as expected. Now the sa_assert line is
> block of the for loop and the switch is no longer inside the loop.
>
> Adding proper {} to the second for loop will fix the problem.


It has python-indentation :-)  I didn't see it... and I'll fix this.

   Stefan

>
> Matthias

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