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Re: [PATCH v2 10/15] qapi: Clean up visitor's recovery from input with i


From: Eric Blake
Subject: Re: [PATCH v2 10/15] qapi: Clean up visitor's recovery from input with invalid type
Date: Fri, 24 Apr 2020 08:57:51 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0

On 4/24/20 3:43 AM, Markus Armbruster wrote:
An alternate type's visit_type_FOO() fails when it runs into an
invalid ->type.  If it's an input visit, we then need to free the the
object we got from visit_start_alternate().  We do that with
qapi_free_FOO(), which uses the dealloc visitor.

Trouble is that object is in a bad state: its ->type is invalid.  So
the dealloc visitor will run into the same error again, and the error
recovery skips deallocating the alternate's (invalid) alternative.
Works, because qapi_free_FOO() ignores the error.

Avoid it instead: free the messed up object with by g_free().

Signed-off-by: Markus Armbruster <address@hidden>
---
  scripts/qapi/visit.py | 3 +++
  1 file changed, 3 insertions(+)

diff --git a/scripts/qapi/visit.py b/scripts/qapi/visit.py
index e3467b770b..678109dfb5 100644
--- a/scripts/qapi/visit.py
+++ b/scripts/qapi/visit.py
@@ -234,6 +234,9 @@ void visit_type_%(c_name)s(Visitor *v, const char *name, 
%(c_name)s **obj, Error
      default:
          error_setg(&err, QERR_INVALID_PARAMETER_TYPE, name ? name : "null",
                     "%(name)s");
+        /* Avoid passing invalid *obj to qapi_free_%(c_name)s() */
+        g_free(*obj);
+        *obj = NULL;

Yep, fixes the problem I spotted in v1, and much easier to review with the reduced scope of change.

Reviewed-by: Eric Blake <address@hidden>

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org




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