[libvirt] [PATCH] virnwfilterbindingobj: Introduce and use virNWFilterBindingObjStealDef

[Michal Privoznik]

https://bugzilla.redhat.com/show_bug.cgi?id=1686927

When trying to create a nwfilter binding via
nwfilterBindingCreateXML() we may encounter a crash. The sequence
of functions called is as follows:

1) nwfilterBindingCreateXML() parses the XML and calls
virNWFilterBindingObjListAdd() which calls
virNWFilterBindingObjListAddLocked()

2) Here, @binding is not found because binding->remove is set.

3) Therefore, controls continue with creating new @binding,
setting its def to the one from 1) and adding it to the hash
table.

4) This fails, because the binding is still in the hash table
(duplicate key is detected).

5) The control jumps to 'error' label where
virNWFilterBindingObjEndAPI() is called which frees the binding
definition passed.

6) Error is propagated to the caller, which calls
virNWFilterBindingDefFree() over the definition again.

The solution is to unset binding->def in case of failure so it's
not freed in step 5).

Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
---

Technically, this is a v2 of:

https://www.redhat.com/archives/libvir-list/2019-March/msg01209.html

But since this one implements different approach than v1 I'm not marking
it as such.

 src/conf/virnwfilterbindingobj.c     | 10 ++++++++++
 src/conf/virnwfilterbindingobj.h     |  3 +++
 src/conf/virnwfilterbindingobjlist.c |  4 ++++
 src/libvirt_private.syms             |  1 +
 4 files changed, 18 insertions(+)

diff --git a/src/conf/virnwfilterbindingobj.c b/src/conf/virnwfilterbindingobj.c
index 23978d4207..68afb9c434 100644
--- a/src/conf/virnwfilterbindingobj.c
+++ b/src/conf/virnwfilterbindingobj.c
@@ -88,6 +88,16 @@ virNWFilterBindingObjSetDef(virNWFilterBindingObjPtr obj,
 }
 
 
+virNWFilterBindingDefPtr
+virNWFilterBindingObjStealDef(virNWFilterBindingObjPtr obj)
+{
+    virNWFilterBindingDefPtr def;
+
+    VIR_STEAL_PTR(def, obj->def);
+    return def;
+}
+
+
 bool
 virNWFilterBindingObjGetRemoving(virNWFilterBindingObjPtr obj)
 {
diff --git a/src/conf/virnwfilterbindingobj.h b/src/conf/virnwfilterbindingobj.h
index 8e5fbee35f..b26bb3c8ec 100644
--- a/src/conf/virnwfilterbindingobj.h
+++ b/src/conf/virnwfilterbindingobj.h
@@ -39,6 +39,9 @@ void
 virNWFilterBindingObjSetDef(virNWFilterBindingObjPtr obj,
                             virNWFilterBindingDefPtr def);
 
+virNWFilterBindingDefPtr
+virNWFilterBindingObjStealDef(virNWFilterBindingObjPtr obj);
+
 bool
 virNWFilterBindingObjGetRemoving(virNWFilterBindingObjPtr obj);
 
diff --git a/src/conf/virnwfilterbindingobjlist.c b/src/conf/virnwfilterbindingobjlist.c
index 06ccbf53af..4ee2c1b194 100644
--- a/src/conf/virnwfilterbindingobjlist.c
+++ b/src/conf/virnwfilterbindingobjlist.c
@@ -167,6 +167,7 @@ virNWFilterBindingObjListAddLocked(virNWFilterBindingObjListPtr bindings,
                                    virNWFilterBindingDefPtr def)
 {
     virNWFilterBindingObjPtr binding;
+    bool stealDef = false;
 
     /* See if a binding with matching portdev already exists */
     if ((binding = virNWFilterBindingObjListFindByPortDevLocked(
@@ -181,6 +182,7 @@ virNWFilterBindingObjListAddLocked(virNWFilterBindingObjListPtr bindings,
         goto error;
 
     virNWFilterBindingObjSetDef(binding, def);
+    stealDef = true;
 
     if (virNWFilterBindingObjListAddObjLocked(bindings, binding) < 0)
         goto error;
@@ -188,6 +190,8 @@ virNWFilterBindingObjListAddLocked(virNWFilterBindingObjListPtr bindings,
     return binding;
 
  error:
+    if (stealDef)
+        virNWFilterBindingObjStealDef(binding);
     virNWFilterBindingObjEndAPI(&binding);
     return NULL;
 }
diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index 26f10bd47f..a33f9e61b1 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -1101,6 +1101,7 @@ virNWFilterBindingObjParseFile;
 virNWFilterBindingObjSave;
 virNWFilterBindingObjSetDef;
 virNWFilterBindingObjSetRemoving;
+virNWFilterBindingObjStealDef;
 
 
 # conf/virnwfilterbindingobjlist.h
-- 
2.19.2