On 07/28/2017 01:19 PM, Pavel Hrdina wrote:
On Fri, Jul 28, 2017 at 12:39:01PM -0400, John Ferlan wrote:
The virObject logic "assumes" that whatever is passed to its API's would be some sort of virObjectPtr; however, if it is not then some really bad things can happen.
So far there's been only virObject{Ref|Unref}, virObject{Lock|Unlock}, and virObjectIsClass and the virObject and virObjectLockable class consumers have been well behaved and code well tested. Soon there will be more consumers and one such consumer tripped over this during testing by passing a virHashTablePtr to virObjectIsClass which ends up calling virClassIsDerivedFrom using "obj->klass", which wasn't really a klass object causing one of those bad things to happen.
To avoid the future possibility that a non virObject class memory was passed to some virObject* API, this patch adds two new checks - one to validate that the object has the 0xCAFExxxx value in obj->->u.s.magic and the other to ensure obj->u.s.magic doesn't "wrap" some day to 0xCAFF0000 if we ever get that many object classes. The check is also moved before the name VIR_STRDUP to avoid the extra VIR_FREE that would be required on the failure path.
This doesn't add any safeguard and for most virObject(Ref|Unref) calls we don't check the return value. This is basically a programming error as well and we should consider start using abort().
And yes, this is the programming error - it was awfully stupid, but IIRC it also didn't "jump out" right away what the problem is/was. It was far worse for *Ref/Unref, but lock was interesting too insomuch as I wouldn't get the lock so perhaps two threads would make a change at the same time and we may never know unless we check lock status.
It is still left up to the caller to handle the failed API calls just as it would be if it passed a NULL opaque pointer anyobj.
And of course this was my escape clause because of void Lock's.
Signed-off-by: John Ferlan <jferlan@redhat.com> --- src/util/virobject.c | 26 +++++++++++++++++++------- 1 file changed, 19 insertions(+), 7 deletions(-)
diff --git a/src/util/virobject.c b/src/util/virobject.c index 2cf4743..dd4c39a 100644 --- a/src/util/virobject.c +++ b/src/util/virobject.c @@ -47,14 +47,21 @@ struct _virClass { virObjectDisposeCallback dispose; };
+#define VIR_OBJECT_NOTVALID(obj) (!obj || ((obj->u.s.magic & 0xCAFE0000) != 0xCAFE0000))
This is not correct, it should be:
((obj->u.s.magic & 0xFFFF0000) != 0xCAFE0000)
Oh right and I see it was a straight cut-n-paste from Dan's reply too: https://www.redhat.com/archives/libvir-list/2017-May/msg01211.html
+ #define VIR_OBJECT_USAGE_PRINT_WARNING(anyobj, objclass) \ do { \ virObjectPtr obj = anyobj; \ - if (!obj) \ - VIR_WARN("Object cannot be NULL"); \ - else \ + if (VIR_OBJECT_NOTVALID(obj)) { \ + if (!obj) \ + VIR_WARN("Object cannot be NULL"); \ + else \ + VIR_WARN("Object %p has a bad magic number %X", \ + obj, obj->u.s.magic); \ + } else { \ VIR_WARN("Object %p (%s) is not a %s instance", \ anyobj, obj->klass->name, #objclass); \ + } \ } while (0)
@@ -177,9 +184,14 @@ virClassNew(virClassPtr parent, goto error;
klass->parent = parent; + klass->magic = virAtomicIntInc(&magicCounter); + if (klass->magic > 0xCAFEFFFF) { + virReportError(VIR_ERR_INTERNAL_ERROR, "%s", + _("too many object classes defined")); + goto error; + }
This will probably never happen :).
Pavel
Agreed, but if it does happen then I'd be the last to touch right... So I'd get the blame. In any case, another one of those Dan suggestions: https://www.redhat.com/archives/libvir-list/2017-May/msg01221.html If this is not desired - that's fine I can drop it. Cannot say I didn't try though. Thanks for the quick review! With a freeze on at least this may give time for others to chime in with thoughts as well. John