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Tsirkin" To: Junjie Cao Cc: qemu-devel@nongnu.org, jasowang@redhat.com, yuri.benditovich@daynix.com, akihiko.odaki@daynix.com, qemu-stable@nongnu.org Subject: Re: [PATCH] virtio-net: validate RSS indirections_len in post_load Message-ID: <20260323094940-mutt-send-email-mst@kernel.org> References: <20260323131531.1976-1-junjie.cao@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260323131531.1976-1-junjie.cao@intel.com> Received-SPF: pass client-ip=170.10.129.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 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: 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 Mon, Mar 23, 2026 at 09:15:31PM +0800, Junjie Cao wrote: > virtio_net_handle_rss() enforces that indirections_len is a non-zero > power of two no larger than VIRTIO_NET_RSS_MAX_TABLE_LEN, but > virtio_net_rss_post_load() applies none of these checks to values > restored from the migration stream. > > A crafted migration stream can set indirections_len to 0. Even if it > also clears redirect, virtio_load() calls set_features_nocheck() after > the device vmstate (including the RSS subsection and its post_load) has > already been loaded, re-deriving redirect from the negotiated guest > features. When VIRTIO_NET_F_RSS was negotiated, redirect is set back > to true regardless of the migration stream value. The receive path > then computes > > hash & (indirections_len - 1) /* wraps to 0xFFFFFFFF via int promotion */ > > and uses the result to index into indirections_table, which was not > allocated by the VMState loader when the element count is zero (see > vmstate_handle_alloc()), resulting in a NULL pointer dereference that > crashes QEMU: > > #0 virtio_net_process_rss ../hw/net/virtio-net.c:1901 > #1 virtio_net_receive_rcu ../hw/net/virtio-net.c:1921 > #2 virtio_net_do_receive ../hw/net/virtio-net.c:2061 > #3 nc_sendv_compat ../net/net.c:823 > #4 qemu_deliver_packet_iov ../net/net.c:870 > > The RSS subsection is only loaded when rss_data.enabled is true (via > virtio_net_rss_needed()), and the command path always produces > indirections_len in {1, 2, 4, …, 128}, so an unconditional check > cannot reject a legitimate migration stream. > > Fixes: e41b711485e5 ("virtio-net: add migration support for RSS and hash report") > Cc: qemu-stable@nongnu.org > Signed-off-by: Junjie Cao Thanks for the patch! Yet something to improve: > --- > hw/net/virtio-net.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c > index 2a5d642a64..3038836098 100644 > --- a/hw/net/virtio-net.c > +++ b/hw/net/virtio-net.c > @@ -3427,6 +3427,15 @@ static int virtio_net_rss_post_load(void *opaque, int version_id) > n->rss_data.supported_hash_types = VIRTIO_NET_RSS_SUPPORTED_HASHES; > } > > + if (n->rss_data.indirections_len == 0 || not needed since it's included in is_power_of_2 check below? > + n->rss_data.indirections_len > VIRTIO_NET_RSS_MAX_TABLE_LEN || > + !is_power_of_2(n->rss_data.indirections_len)) { with == 0 removed, the logic is duplicated from virtio_net_device_realize. How about factoring it out to a helper? > + error_report("virtio-net: saved image has invalid RSS " > + "indirections_len: %u", > + n->rss_data.indirections_len); > + return -EINVAL; > + } > + > return 0; > } > > -- > 2.43.0