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[79.177.145.168]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-46c1ee0189esm24669051f8f.9.2026.06.26.03.32.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 26 Jun 2026 03:32:27 -0700 (PDT) Date: Fri, 26 Jun 2026 06:32:24 -0400 From: "Michael S. Tsirkin" To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= Cc: Mauro Matteo Cascella , Laurent Vivier , qemu-devel@nongnu.org, Paolo Bonzini , Amit Shah , =?iso-8859-1?Q?Marc-Andr=E9?= Lureau , qemu-stable@nongnu.org Subject: Re: [PATCH] hw/char/virtio-serial-bus: fix guest-triggerable OOM in control_out() Message-ID: <20260626063111-mutt-send-email-mst@kernel.org> References: <20260622161144.2883799-1-lvivier@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: 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: 8 X-Spam_score: 0.8 X-Spam_bar: / X-Spam_report: (0.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.445, 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Fri, Jun 26, 2026 at 10:43:05AM +0100, Daniel P. Berrangé wrote: > On Thu, Jun 25, 2026 at 06:56:05PM +0200, Mauro Matteo Cascella wrote: > > On Mon, Jun 22, 2026 at 6:30 PM Daniel P. Berrangé wrote: > > > > > > On Mon, Jun 22, 2026 at 06:11:44PM +0200, Laurent Vivier wrote: > > > > A malicious guest can craft virtqueue descriptors with arbitrary lengths. > > > > control_out() calls iov_size() on the guest-supplied scatter-gather list > > > > and passes the result directly to g_malloc(), allowing a guest to force > > > > QEMU to attempt multi-gigabyte allocations and crash the host process. > > > > > > > > Fix this by copying at most sizeof(struct virtio_console_control) into a > > > > stack-local variable instead of allocating a buffer sized by the guest. > > > > handle_control_message() only accesses the fixed-size id, event, and > > > > value fields, so no data beyond the struct was ever needed. > > > > > > Does anyone have thoughts on whether we should treat guest initiated > > > unbounded allocs as a security issue ? > > > > > > IIUC, this flaw would require root in the guest OS in order to craft > > > the malicious virtqueue descriptors. > > > > > > A self-initiated crash triggered by root would not historically > > > be enough justification for CVE. We would require it to be triggered > > > by unprivileged user. > > > > > > Nested virt with device assignment could change that equation though > > > as the L2 guest could be considered an unpriv user from the L1 POV. > > > > > > Also in theory the large alloc might be large enough to consume all > > > host RAM but not large enough to trigger OOM kill of QEMU. This might > > > impact operation of other co-located VMs on the same host. > > > > > > Anyone think this is bad enough to justify a CVE ? Or should we treat > > > these OOM scenarios maerely as "hardening" bugs, where they require > > > 'root' in the L1 guest ? > > > > I'd lean toward classifying these as hardening bugs. I don't see the > > point in assigning Low CVEs to these kinds of issues nowadays. Under > > current vulnerability management standards, they would definitely be > > pushed down the priority list and likely skipped or deferred. > > Ok, so lets apply as a general rule that all OOM bugs which require > privileged access in the guest are not assigned CVEs. > > An unprivileged guest exploit would be more significant so still > potentially in scope. > > > With regards, > Daniel I'd love to have a document where all this is written up, though. > -- > |: https://berrange.com ~~ https://hachyderm.io/@berrange :| > |: https://libvirt.org ~~ https://entangle-photo.org :| > |: https://pixelfed.art/berrange ~~ https://fstop138.berrange.com :|