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Wed, 5 Aug 2020 14:16:58 +0000 (UTC) Date: Wed, 5 Aug 2020 16:16:57 +0200 From: Kevin Wolf To: Alberto Garcia Subject: Re: [PATCH] qcow2-cluster: Fix integer left shift error in qcow2_alloc_cluster_link_l2() Message-ID: <20200805141657.GA37318@linux.fritz.box> References: <81ba90fe0c014f269621c283269b42ad@h3c.com> MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=kwolf@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=205.139.110.61; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/05 04:10:11 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Chengchiwen , Tuguoyi , "qemu-block@nongnu.org" , "qemu-devel@nongnu.org" , "mreitz@redhat.com" , Gaoliang Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 05.08.2020 um 15:44 hat Alberto Garcia geschrieben: > On Wed 05 Aug 2020 11:22:58 AM CEST, Tuguoyi wrote: > > This patch fix it by casting @i to uint64_t before doing left shift > > operation > > The patch seems fine and I also think that it's perhaps worth a test > case (although it only seems to happen with preallocation=falloc or full > so the test would need to generate very large files). > > But I also wonder if there are other cases where this can happen. > > nb_clusters is an int and there are more cases of > > nb_clusters << s->cluster_bits > > I can see at least these: handle_alloc(), qcow2_free_any_clusters(), > qcow2_alloc_cluster_abort(). Actuallyx, handle_alloc() and everything that comes from it should be fine. It has a uint64_t nb_clusters locally and limits it: nb_clusters = MIN(nb_clusters, INT_MAX >> s->cluster_bits); The problematic request that causes the crash comes actually from qcow2_co_truncate(). It limits it only to s->l2_slice_size, which can be larger than that, but will be at most 256k (= 2 MB / sizeof(uint64_t)). cow_end.offset will get a wraparound then, too. This is harmless because cow_end.nb_bytes = 0, so the offset will be ignored anyway. I think the proper fix to be made in the 5.2 release cycle would revert this one and instead fix the limit in qcow2_co_truncate(). But this one is good enough as a band-aid for 5.1. Kevin