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Tsirkin" To: qemu-devel@nongnu.org Cc: Peter Maydell , Hawkins Jiawei , Eugenio =?utf-8?b?UMOpcmV6?= , Jason Wang Subject: [PULL 49/66] vdpa: Fix possible use-after-free for VirtQueueElement Message-ID: <031b1abacbdb3f4e016b6b926f7e7876c05339bb.1689030052.git.mst@redhat.com> References: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-Mailer: git-send-email 2.27.0.106.g8ac3dc51b1 X-Mutt-Fcc: =sent 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_H4=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: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org From: Hawkins Jiawei QEMU uses vhost_handle_guest_kick() to forward guest's available buffers to the vdpa device in SVQ avail ring. In vhost_handle_guest_kick(), a `g_autofree` `elem` is used to iterate through the available VirtQueueElements. This `elem` is then passed to `svq->ops->avail_handler`, specifically to the vhost_vdpa_net_handle_ctrl_avail(). If this handler fails to process the CVQ command, vhost_handle_guest_kick() regains ownership of the `elem`, and either frees it or requeues it. Yet the problem is that, vhost_vdpa_net_handle_ctrl_avail() mistakenly frees the `elem`, even if it fails to forward the CVQ command to vdpa device. This can result in a use-after-free for the `elem` in vhost_handle_guest_kick(). This patch solves this problem by refactoring vhost_vdpa_net_handle_ctrl_avail() to only freeing the `elem` if it owns it. Fixes: bd907ae4b0 ("vdpa: manual forward CVQ buffers") Signed-off-by: Hawkins Jiawei Message-Id: Reviewed-by: Eugenio Pérez Reviewed-by: Michael S. Tsirkin Signed-off-by: Michael S. Tsirkin --- net/vhost-vdpa.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c index 679ef4bed0..5542b47a8f 100644 --- a/net/vhost-vdpa.c +++ b/net/vhost-vdpa.c @@ -831,7 +831,16 @@ out: error_report("Bad device CVQ written length"); } vhost_svq_push_elem(svq, elem, MIN(in_len, sizeof(status))); - g_free(elem); + /* + * `elem` belongs to vhost_vdpa_net_handle_ctrl_avail() only when + * the function successfully forwards the CVQ command, indicated + * by a non-negative value of `dev_written`. Otherwise, it still + * belongs to SVQ. + * This function should only free the `elem` when it owns. + */ + if (dev_written >= 0) { + g_free(elem); + } return dev_written < 0 ? dev_written : 0; }