[PATCH] qemu_capabilities: Pass pointer to va_list in virQEMUCapsSetVAList

[Michal Privoznik <mprivozn@xxxxxxxxxx>]

There is one specific caller (testInfoSetArgs() in
qemuxml2argvtest.c) which expect the  va_list argument to change
after returning from the virQEMUCapsSetVAList() function.
However, since we are passing plain va_list this is not
guaranteed. The man page of stdarg(3) says:

  If ap is passed to a function that uses va_arg(ap,type), then
  the value of ap is undefined after the return of that function.

(ap is a variable of type va_list)

I've seen this in action in fact: on i686 the qemuxml2argvtest
fails on the second test case because testInfoSetArgs() sees
ARG_QEMU_CAPS and callse virQEMUCapsSetVAList to process the
capabilities (in this case there's just one
QEMU_CAPS_SECCOMP_BLACKLIST). But since the changes are not
reflected in the caller, in the next iteration testInfoSetArgs()
sees the qemu capability and not ARG_END.

Signed-off-by: Michal Privoznik <mprivozn@xxxxxxxxxx>
---

This passed successfully on x86_64 and i686 in my testing.

 src/qemu/qemu_capabilities.c | 6 +++---
 src/qemu/qemu_capabilities.h | 2 +-
 tests/qemuxml2argvtest.c     | 2 +-
 3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
index c5954edaf0..e182a2c2e5 100644
--- a/src/qemu/qemu_capabilities.c
+++ b/src/qemu/qemu_capabilities.c
@@ -1665,11 +1665,11 @@ virQEMUCapsSet(virQEMUCapsPtr qemuCaps,
 
 void
 virQEMUCapsSetVAList(virQEMUCapsPtr qemuCaps,
-                     va_list list)
+                     va_list *list)
 {
     int flag;
 
-    while ((flag = va_arg(list, int)) < QEMU_CAPS_LAST)
+    while ((flag = va_arg(*list, int)) < QEMU_CAPS_LAST)
         ignore_value(virBitmapSetBit(qemuCaps->flags, flag));
 }
 
@@ -1680,7 +1680,7 @@ virQEMUCapsSetList(virQEMUCapsPtr qemuCaps, ...)
     va_list list;
 
     va_start(list, qemuCaps);
-    virQEMUCapsSetVAList(qemuCaps, list);
+    virQEMUCapsSetVAList(qemuCaps, &list);
     va_end(list);
 }
 
diff --git a/src/qemu/qemu_capabilities.h b/src/qemu/qemu_capabilities.h
index 7625d754a3..ceab8c9154 100644
--- a/src/qemu/qemu_capabilities.h
+++ b/src/qemu/qemu_capabilities.h
@@ -519,7 +519,7 @@ void virQEMUCapsSet(virQEMUCapsPtr qemuCaps,
                     virQEMUCapsFlags flag) ATTRIBUTE_NONNULL(1);
 
 void virQEMUCapsSetVAList(virQEMUCapsPtr qemuCaps,
-                          va_list list) ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2);
+                          va_list *list) ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2);
 void virQEMUCapsSetList(virQEMUCapsPtr qemuCaps, ...) ATTRIBUTE_NONNULL(1);
 
 void virQEMUCapsClear(virQEMUCapsPtr qemuCaps,
diff --git a/tests/qemuxml2argvtest.c b/tests/qemuxml2argvtest.c
index 6e7d1b0b9a..a7a8d77e1d 100644
--- a/tests/qemuxml2argvtest.c
+++ b/tests/qemuxml2argvtest.c
@@ -650,7 +650,7 @@ testInfoSetArgs(struct testInfo *info,
         case ARG_QEMU_CAPS:
             if (qemuCaps || !(qemuCaps = virQEMUCapsNew()))
                 goto cleanup;
-            virQEMUCapsSetVAList(qemuCaps, argptr);
+            virQEMUCapsSetVAList(qemuCaps, &argptr);
             break;
 
         case ARG_GIC:
-- 
2.19.2

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