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Tsirkin" To: qemu-devel@nongnu.org Subject: [PATCH] qom: assert integer does not overflow Message-ID: <20220225140955.63949-1-mst@redhat.com> MIME-Version: 1.0 X-Mailer: git-send-email 2.27.0.106.g8ac3dc51b1 X-Mutt-Fcc: =sent Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=170.10.133.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Eduardo Habkost , Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= , Jason Wang , Victor Tom , Paolo Bonzini , Stefano Garzarella Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" QOM reference counting is not designed with an infinite amount of references in mind, trying to take a reference in a loop will overflow the integer. We will then eventually assert when dereferencing, but the real problem is in object_ref so let's assert there to make such issues cleaner and easier to debug. Some micro-benchmarking shows using fetch and add this is essentially free on x86. Signed-off-by: Michael S. Tsirkin --- qom/object.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/qom/object.c b/qom/object.c index 4f0677cca9..5db3974f04 100644 --- a/qom/object.c +++ b/qom/object.c @@ -1167,10 +1167,14 @@ GSList *object_class_get_list_sorted(const char *implements_type, Object *object_ref(void *objptr) { Object *obj = OBJECT(objptr); + uint32_t ref; + if (!obj) { return NULL; } - qatomic_inc(&obj->ref); + ref = qatomic_fetch_inc(&obj->ref); + /* Assert waaay before the integer overflows */ + g_assert(ref < INT_MAX); return obj; } -- MST