[PATCH v2 19/29] hw/vfio/container: Fix missing ERRP_GUARD() for error_prepend()

[Zhao Liu]

From: Zhao Liu <zhao1.liu@intel.com>

As the comment in qapi/error, passing @errp to error_prepend() requires
ERRP_GUARD():

* = Why, when and how to use ERRP_GUARD() =
*
* Without ERRP_GUARD(), use of the @errp parameter is restricted:
...
* - It should not be passed to error_prepend(), error_vprepend() or
*   error_append_hint(), because that doesn't work with &error_fatal.
* ERRP_GUARD() lifts these restrictions.
*
* To use ERRP_GUARD(), add it right at the beginning of the function.
* @errp can then be used without worrying about the argument being
* NULL or &error_fatal.

ERRP_GUARD() could avoid the case when @errp is &error_fatal, the user
can't see this additional information, because exit() happens in
error_setg earlier than information is added [1].

The vfio_get_group() passes @errp to error_prepend(). Its @errp is
from vfio_attach_device(), and there are too many possible callers to
check the impact of this defect; it may or may not be harmless. Thus it
is necessary to protect @errp with ERRP_GUARD().

To avoid the issue like [1] said, add missing ERRP_GUARD() at the
beginning of this function.

[1]: Issue description in the commit message of commit ae7c80a7bd73
     ("error: New macro ERRP_GUARD()").

Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: "Cédric Le Goater" <clg@redhat.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
---
v2: Use Markus' sentence to polish commit message. (Markus)
---
 hw/vfio/container.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/hw/vfio/container.c b/hw/vfio/container.c
index bd25b9fbad2e..f66bb01f5b18 100644
--- a/hw/vfio/container.c
+++ b/hw/vfio/container.c
@@ -719,6 +719,7 @@ static void vfio_disconnect_container(VFIOGroup *group)
 
 static VFIOGroup *vfio_get_group(int groupid, AddressSpace *as, Error **errp)
 {
+    ERRP_GUARD();
     VFIOGroup *group;
     char path[32];
     struct vfio_group_status status = { .argsz = sizeof(status) };
-- 
2.34.1