qom: suppress conscan warning of returning null point

Conscan complains about g_malloc0() and malloc() return null.

  Error: NULL_RETURNS (CWE-476):
  qemu-kvm/qom/object.c:239: returned_null: Function "g_malloc0(gsize)" returns null.
  qemu-kvm/qom/object.c:239: var_assigned: Assigning: "ti->class" = null return value from "g_malloc0(gsize)".
  qemu-kvm/qom/object.c:249: dereference: Dereferencing a null pointer "ti->class".

But if the passed size parameter is >= 1, then we can always get an
effective pointer, the warning disappears.

Signed-off-by: Amos Kong <akong@redhat.com>
---
 qom/object.c | 2 ++
 1 file changed, 2 insertions(+)

> Subject: [Qemu-devel] [PATCH] qom: suppress conscan warning of returning null
> point
> 
> Conscan complains about g_malloc0() and malloc() return null.
> 
>   Error: NULL_RETURNS (CWE-476):
>   qemu-kvm/qom/object.c:239: returned_null: Function "g_malloc0(gsize)"
> returns null.
>   qemu-kvm/qom/object.c:239: var_assigned: Assigning: "ti->class" = null
> return value from "g_malloc0(gsize)".
>   qemu-kvm/qom/object.c:249: dereference: Dereferencing a null pointer
> "ti->class".
> 
> But if the passed size parameter is >= 1, then we can always get an
> effective pointer, the warning disappears.
> 
> Signed-off-by: Amos Kong <akong@redhat.com>
> ---
>  qom/object.c | 2 ++
>  1 file changed, 2 insertions(+)
> 

Reviewed-by: Gonglei <arei.gonglei@huawei.com>

Best regards,
-Gonglei

Il 20/09/2014 02:11, Amos Kong ha scritto:
> Conscan complains about g_malloc0() and malloc() return null.
> 
>   Error: NULL_RETURNS (CWE-476):
>   qemu-kvm/qom/object.c:239: returned_null: Function "g_malloc0(gsize)" returns null.
>   qemu-kvm/qom/object.c:239: var_assigned: Assigning: "ti->class" = null return value from "g_malloc0(gsize)".
>   qemu-kvm/qom/object.c:249: dereference: Dereferencing a null pointer "ti->class".
> 
> But if the passed size parameter is >= 1, then we can always get an
> effective pointer, the warning disappears.

The model should handle it:

void *
g_malloc0(size_t n_bytes)
{
    void *mem;
    __coverity_negative_sink__(n_bytes);
    mem = calloc(1, n_bytes == 0 ? 1 : n_bytes);
    if (!mem) __coverity_panic__();
    return mem;
}

So this patch means your coverity runs are misconfigured.

Paolo

Paolo Bonzini <pbonzini@redhat.com> writes:

> Il 20/09/2014 02:11, Amos Kong ha scritto:
>> Conscan complains about g_malloc0() and malloc() return null.

s/Conscan/Coverity/, both here and in subject.

>> 
>>   Error: NULL_RETURNS (CWE-476):
>>   qemu-kvm/qom/object.c:239: returned_null: Function
>> "g_malloc0(gsize)" returns null.
>>   qemu-kvm/qom/object.c:239: var_assigned: Assigning: "ti->class" =
>> null return value from "g_malloc0(gsize)".
>>   qemu-kvm/qom/object.c:249: dereference: Dereferencing a null
>> pointer "ti->class".
>> 
>> But if the passed size parameter is >= 1, then we can always get an
>> effective pointer, the warning disappears.
>
> The model should handle it:
>
> void *
> g_malloc0(size_t n_bytes)
> {
>     void *mem;
>     __coverity_negative_sink__(n_bytes);
>     mem = calloc(1, n_bytes == 0 ? 1 : n_bytes);
>     if (!mem) __coverity_panic__();
>     return mem;
> }
>
> So this patch means your coverity runs are misconfigured.

Yes.  I'm not sure we want the assertions anyway.

I use the following options with cov-analyze:

    -co BAD_FREE:allow_first_field:true
    -co DEADCODE:no_dead_default:true
    --security
    --concurrency
    --user-model-file scripts/coverity-model.xmldb
    --derived-model-file ~/work/glib/glib-2.38.2.xmldb

where glib-2.38.2.xmldb is produced by "cov-collect-models --dir cov -of
glib-2.32.4.xmldb" after a full Coverity scan of glib.