[PATCH] vl: fix leak of qdict_crumple return value

[PATCH] vl: fix leak of qdict_crumple return value

[Paolo Bonzini]

Coverity reports that qemu_parse_config_group is returning without
unrefing the "crumpled" dictionary in case its top level item is a
list.  But actually the contract with qemu_record_config_group is
the same as for qemu_parse_config_group itself: if those function
need to stash the dictionary they get, they have to take a reference
themselves (currently this is never the case for either function).
Therefore, just add an unconditional qobject_unref(crumpled) to
qemu_parse_config_group.

Reported-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 softmmu/vl.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/softmmu/vl.c b/softmmu/vl.c
index 2004d57108..7b54ddf6f4 100644
--- a/softmmu/vl.c
+++ b/softmmu/vl.c
@@ -2196,9 +2196,10 @@ static void qemu_parse_config_group(const char *group, QDict *qdict,
     if (qobject_type(crumpled) != QTYPE_QDICT) {
         assert(qobject_type(crumpled) == QTYPE_QLIST);
         error_setg(errp, "Lists cannot be at top level of a configuration section");
-        return;
+    } else {
+        qemu_record_config_group(group, qobject_to(QDict, crumpled), false, errp);
     }
-    qemu_record_config_group(group, qobject_to(QDict, crumpled), false, errp);
+    qobject_unref(crumpled);
 }
 
 static void qemu_read_default_config_file(Error **errp)
-- 
2.31.1

Re: [PATCH] vl: fix leak of qdict_crumple return value

[Markus Armbruster]

Paolo Bonzini <pbonzini@redhat.com> writes:

> Coverity reports that qemu_parse_config_group is returning without
> unrefing the "crumpled" dictionary in case its top level item is a
> list.  But actually the contract with qemu_record_config_group is
> the same as for qemu_parse_config_group itself: if those function
> need to stash the dictionary they get, they have to take a reference
> themselves (currently this is never the case for either function).
> Therefore, just add an unconditional qobject_unref(crumpled) to
> qemu_parse_config_group.
>
> Reported-by: Peter Maydell <peter.maydell@linaro.org>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Do we want

  Fixes: c0d4aa82f895af67cbf7772324e05605e22b4162

here?

> ---
>  softmmu/vl.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/softmmu/vl.c b/softmmu/vl.c
> index 2004d57108..7b54ddf6f4 100644
> --- a/softmmu/vl.c
> +++ b/softmmu/vl.c
> @@ -2196,9 +2196,10 @@ static void qemu_parse_config_group(const char *group, QDict *qdict,
>      if (qobject_type(crumpled) != QTYPE_QDICT) {
>          assert(qobject_type(crumpled) == QTYPE_QLIST);
>          error_setg(errp, "Lists cannot be at top level of a configuration section");
> -        return;
> +    } else {
> +        qemu_record_config_group(group, qobject_to(QDict, crumpled), false, errp);
>      }
> -    qemu_record_config_group(group, qobject_to(QDict, crumpled), false, errp);
> +    qobject_unref(crumpled);
>  }
>  
>  static void qemu_read_default_config_file(Error **errp)

Minimally invasive fix, but the result is a bit awkward.  Possibly
neater:

       if (qobject_type(crumpled) == QTYPE_QLIST) {
           error_setg(errp,
                      "Lists cannot be at top level of a configuration section");
       } else {
           assert(qobject_type(crumpled) == QTYPE_QDICT);
           qemu_record_config_group(group, qobject_to(QDict, crumpled),
                                    false, errp);
       }
       qobject_unref(crumpled);

Regardless:
Reviewed-by: Markus Armbruster <armbru@redhat.com>

Re: [PATCH] vl: fix leak of qdict_crumple return value

[Paolo Bonzini]

On 08/07/21 11:05, Markus Armbruster wrote:
> Fixes: c0d4aa82f895af67cbf7772324e05605e22b4162

Good point, will add.

Paolo

Re: [PATCH] vl: fix leak of qdict_crumple return value

[Paolo Bonzini]

On 08/07/21 11:05, Markus Armbruster wrote:
> Minimally invasive fix, but the result is a bit awkward.  Possibly
> neater:
> 
>         if (qobject_type(crumpled) == QTYPE_QLIST) {
>             error_setg(errp,
>                        "Lists cannot be at top level of a configuration section");
>         } else {
>             assert(qobject_type(crumpled) == QTYPE_QDICT);
>             qemu_record_config_group(group, qobject_to(QDict, crumpled),
>                                      false, errp);
>         }
>         qobject_unref(crumpled);

Even better:

     switch (qobject_type(crumpled)) {
     case QTYPE_QDICT:
         qemu_record_config_group(group, qobject_to(QDict, crumpled), false, errp);
         break;
     case QTYPE_QLIST:
         error_setg(errp, "Lists cannot be at top level of a configuration section");
         break;
     default:
         g_assert_unreachable();
     }

Paolo