[libvirt] [PATCH] vircgroup: fix NULL pointer dereferencing

[Marc Hartmayer]

On Thu, Sep 27, 2018 at 02:38 PM +0200, John Ferlan <jferlan at redhat.com> wrote:
> $subj:
>
> util: Fix cgroup processing NULL pointer dereferencing

I’m fine with this change :)

>
>
> On 9/26/18 11:53 AM, Marc Hartmayer wrote:
>> When virCgroupEnableMissingControllers fails it's possible that *group
>> is still set to NULL. Therefore let's add a guard and an attribute for
>> this.
>
> Prefix paragraph with rather than at the bottom "Fixes:".

Okay.

>
> Introduced by commit 1602aa28f,
>
>>
>>  [#0] virCgroupRemove(group=0x0)
>>  [#1] virCgroupNewMachineSystemd
>>  [#2] virCgroupNewMachine
>>  [#3] qemuInitCgroup
>>  [#4] qemuSetupCgroup
>>  [#5] qemuProcessLaunch
>>  [#6] qemuProcessStart
>>  [#7] qemuDomainObjStart
>>  [#8] qemuDomainCreateWithFlags
>>  [#9] qemuDomainCreate
>>  ...
>>
>> Fixes: 1602aa28f820ada66f707cef3e536e8572fbda1e
>
> I think it's safe to remove the stack trace...

Okay.

>
>> Reviewed-by: Boris Fiuczynski <fiuczy at linux.ibm.com>
>> Reviewed-by: Bjoern Walk <bwalk at linux.ibm.com>
>> Signed-off-by: Marc Hartmayer <mhartmay at linux.ibm.com>
>> ---
>>  src/util/vircgroup.c | 3 ++-
>>  src/util/vircgroup.h | 3 ++-
>>  2 files changed, 4 insertions(+), 2 deletions(-)
>
> While this patch is correct to remove the NULL deref, there "may" be a
> problem with the patch that introduced this. Rather than usurp this
> thread, I'll respond to the other one and see where it takes us.

Okay.

>
> John
>
>>
>> diff --git a/src/util/vircgroup.c b/src/util/vircgroup.c
>> index 23957c82c7fa..06e1d158febb 100644
>> --- a/src/util/vircgroup.c
>> +++ b/src/util/vircgroup.c
>> @@ -1104,7 +1104,8 @@ virCgroupNewMachineSystemd(const char *name,
>>
>>   error:
>>      saved = virSaveLastError();
>> -    virCgroupRemove(*group);
>> +    if (*group)
>> +        virCgroupRemove(*group);
>>      virCgroupFree(group);
>>      if (saved) {
>>          virSetError(saved);
>> diff --git a/src/util/vircgroup.h b/src/util/vircgroup.h
>> index 1f676f21c380..9e1ae3706b1e 100644
>> --- a/src/util/vircgroup.h
>> +++ b/src/util/vircgroup.h
>> @@ -268,7 +268,8 @@ int virCgroupGetCpusetMemoryMigrate(virCgroupPtr group, bool *migrate);
>>  int virCgroupSetCpusetCpus(virCgroupPtr group, const char *cpus);
>>  int virCgroupGetCpusetCpus(virCgroupPtr group, char **cpus);
>>
>> -int virCgroupRemove(virCgroupPtr group);
>> +int virCgroupRemove(virCgroupPtr group)
>> +    ATTRIBUTE_NONNULL(1);
>
> FWIW: This only helps if someone tried to call virCgroupRemove(NULL); it
> doesn't help if the parameter itself is NULL. One could add a "if
> (!group) return 0" to virCgroupRemove to avoid.

Thanks for pointing this out! :) I thought it could help Coverity.

>
>>
>>  int virCgroupKillRecursive(virCgroupPtr group, int signum);
>>  int virCgroupKillPainfully(virCgroupPtr group);
>>
>
--
Kind regards / Beste Grüße
   Marc Hartmayer

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