From 7f87763f47a3c22fb50265a00619ef10f2394b18 Mon Sep 17 00:00:00 2001 From: Berkant Koc Date: Sat, 23 May 2026 15:27:47 +0200 Subject: [PATCH] drm/hyperv: validate VMBus packet size in receive callback hyperv_receive_sub() reads msg->vid_hdr.type and dispatches into one of four message-type branches without knowing how many bytes the host wrote into hv->recv_buf. The completion path then runs memcpy(hv->init_buf, msg, VMBUS_MAX_PACKET_SIZE), so the consumer that wakes on wait_for_completion_timeout() can read up to 16 KiB of residue from a prior message as if it were the response payload. Pass bytes_recvd into hyperv_receive_sub() and reject any packet that does not cover the pipe + synthvid header. A single switch on msg->vid_hdr.type then computes the type-specific payload size: the three completion-driving types (SYNTHVID_VERSION_RESPONSE, SYNTHVID_RESOLUTION_RESPONSE, SYNTHVID_VRAM_LOCATION_ACK) fall through to a shared exit that requires that size before memcpy/complete, while SYNTHVID_FEATURE_CHANGE validates its own payload and returns before reading is_dirt_needed. Unknown types are dropped. SYNTHVID_RESOLUTION_RESPONSE is variable length: the host fills resolution_count entries, not the full SYNTHVID_MAX_RESOLUTION_COUNT array. Validate the fixed prefix first so resolution_count can be read, bound it against the array, then require only the count-sized array, so the shorter responses the host actually sends are accepted. Only run the sub-handler when vmbus_recvpacket() returned success. The memcpy length is bytes_recvd, which is bounded by VMBUS_MAX_PACKET_SIZE only on a successful receive; on -ENOBUFS vmbus_recvpacket() instead reports the required length, which can exceed hv->recv_buf, so copying bytes_recvd would read and write past the 16 KiB buffers. Gating on the success return keeps the copy bounded. The nonzero-return path is itself a malformed-message case and is now logged rather than silently skipped; channel recovery is not attempted. Rejected packets are reported via drm_err_ratelimited() rather than silently dropped, matching the CoCo-hardened pattern in hv_kvp_onchannelcallback(). Fixes: 76c56a5affeb ("drm/hyperv: Add DRM driver for hyperv synthetic video device") Cc: stable@vger.kernel.org # 5.14+ Signed-off-by: Berkant Koc Assisted-by: Claude:claude-opus-4-7 berkoc-pipeline Reviewed-by: Michael Kelley Tested-by: Michael Kelley Signed-off-by: Hamza Mahfooz Link: https://patch.msgid.link/8200dbc199c7a9b75ac7e8af6c748d2189b5ebd5.1779542874.git.me@berkoc.com --- drivers/gpu/drm/hyperv/hyperv_drm_proto.c | 100 +++++++++++++++++++--- 1 file changed, 87 insertions(+), 13 deletions(-) diff --git a/drivers/gpu/drm/hyperv/hyperv_drm_proto.c b/drivers/gpu/drm/hyperv/hyperv_drm_proto.c index c3d0ff229e3d..4e6f703a1b33 100644 --- a/drivers/gpu/drm/hyperv/hyperv_drm_proto.c +++ b/drivers/gpu/drm/hyperv/hyperv_drm_proto.c @@ -420,30 +420,92 @@ static int hyperv_get_supported_resolution(struct hv_device *hdev) return 0; } -static void hyperv_receive_sub(struct hv_device *hdev) +static void hyperv_receive_sub(struct hv_device *hdev, u32 bytes_recvd) { struct hyperv_drm_device *hv = hv_get_drvdata(hdev); struct synthvid_msg *msg; + size_t hdr_size; + size_t need; if (!hv) return; - msg = (struct synthvid_msg *)hv->recv_buf; - - /* Complete the wait event */ - if (msg->vid_hdr.type == SYNTHVID_VERSION_RESPONSE || - msg->vid_hdr.type == SYNTHVID_RESOLUTION_RESPONSE || - msg->vid_hdr.type == SYNTHVID_VRAM_LOCATION_ACK) { - memcpy(hv->init_buf, msg, VMBUS_MAX_PACKET_SIZE); - complete(&hv->wait); + hdr_size = sizeof(struct pipe_msg_hdr) + + sizeof(struct synthvid_msg_hdr); + if (bytes_recvd < hdr_size) { + drm_err_ratelimited(&hv->dev, + "synthvid packet too small for header: %u\n", + bytes_recvd); return; } - if (msg->vid_hdr.type == SYNTHVID_FEATURE_CHANGE) { + msg = (struct synthvid_msg *)hv->recv_buf; + need = hdr_size; + + switch (msg->vid_hdr.type) { + case SYNTHVID_VERSION_RESPONSE: + need += sizeof(struct synthvid_version_resp); + break; + case SYNTHVID_RESOLUTION_RESPONSE: + /* + * The resolution response is variable length: the host + * fills resolution_count entries, not the full + * SYNTHVID_MAX_RESOLUTION_COUNT array. Require the fixed + * prefix first so resolution_count can be read, then + * demand exactly the count-sized array. + */ + need += offsetof(struct synthvid_supported_resolution_resp, + supported_resolution); + if (bytes_recvd < need) + break; + if (msg->resolution_resp.resolution_count > + SYNTHVID_MAX_RESOLUTION_COUNT) { + drm_err_ratelimited(&hv->dev, + "synthvid resolution count too large: %u\n", + msg->resolution_resp.resolution_count); + return; + } + need += msg->resolution_resp.resolution_count * + sizeof(struct hvd_screen_info); + break; + case SYNTHVID_VRAM_LOCATION_ACK: + need += sizeof(struct synthvid_vram_location_ack); + break; + case SYNTHVID_FEATURE_CHANGE: + /* + * Not a completion-driving message: validate its own payload + * and consume it here rather than falling through to the + * memcpy/complete shared by the wait-event responses. + */ + if (bytes_recvd < need + + sizeof(struct synthvid_feature_change)) { + drm_err_ratelimited(&hv->dev, + "synthvid feature change packet too small: %u\n", + bytes_recvd); + return; + } hv->dirt_needed = msg->feature_chg.is_dirt_needed; if (hv->dirt_needed) hyperv_hide_hw_ptr(hv->hdev); + return; + default: + return; } + + /* + * Shared completion path for the wait-event responses + * (VERSION_RESPONSE, RESOLUTION_RESPONSE, VRAM_LOCATION_ACK): + * require the type-specific payload before handing the buffer to + * the waiter. + */ + if (bytes_recvd < need) { + drm_err_ratelimited(&hv->dev, + "synthvid packet too small for type %u: %u < %zu\n", + msg->vid_hdr.type, bytes_recvd, need); + return; + } + memcpy(hv->init_buf, msg, bytes_recvd); + complete(&hv->wait); } static void hyperv_receive(void *ctx) @@ -464,9 +526,21 @@ static void hyperv_receive(void *ctx) ret = vmbus_recvpacket(hdev->channel, recv_buf, VMBUS_MAX_PACKET_SIZE, &bytes_recvd, &req_id); - if (bytes_recvd > 0 && - recv_buf->pipe_hdr.type == PIPE_MSG_DATA) - hyperv_receive_sub(hdev); + if (ret) { + /* + * A nonzero return (e.g. -ENOBUFS for an oversized + * packet) is itself a malformed message: bytes_recvd + * then reports the required length rather than a copied + * payload, so it must not be forwarded to the + * sub-handler. Channel recovery is not attempted. + */ + drm_err_ratelimited(&hv->dev, + "vmbus_recvpacket failed: %d (need %u)\n", + ret, bytes_recvd); + } else if (bytes_recvd > 0 && + recv_buf->pipe_hdr.type == PIPE_MSG_DATA) { + hyperv_receive_sub(hdev, bytes_recvd); + } } while (bytes_recvd > 0 && ret == 0); }