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

[John Ferlan]

$subj:

util: Fix cgroup processing NULL pointer dereferencing


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:".

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...

> 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.

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.

>  
>  int virCgroupKillRecursive(virCgroupPtr group, int signum);
>  int virCgroupKillPainfully(virCgroupPtr group);
>