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Mon, 12 Oct 2026 07:08:41 -0700 (PDT) X-Received: by 2002:a05:600c:3b2a:b0:4a0:2540:b46 with SMTP id 5b1f17b1804b1-4a18e4aca94mr175141615e9.12.1791814120520; Mon, 12 Oct 2026 07:08:40 -0700 (PDT) From: Tommaso Califano To: qemu-devel@nongnu.org Cc: qemu-stable@nongnu.org, Junjie Cao , =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= , Abizer Lokhandwala , Thomas Huth , Tommaso Califano Subject: [PATCH] hw/usb/dev-mtp: Fix assert crash on undersized BULK IN Date: Mon, 12 Oct 2026 16:08:38 +0200 Message-ID: <20261012140839.93559-1-tcalifano@redhat.com> X-Mailer: git-send-email 2.56.0 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists1p.gnu.org; Received-SPF: pass client-ip=170.10.133.124; envelope-from=tcalifano@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -22 X-Spam_score: -2.3 X-Spam_bar: -- X-Spam_report: (-2.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.24, 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, 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+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1791814154087158500 Content-Type: text/plain; charset="utf-8" The EP_DATA_IN result path serializes the queued response as a 12 byte MTP container header followed by one 4 byte word per result argument (12 + 4 * argc bytes). The entry check at the top of the function only verifies that the guest-provided transfer buffer holds at least the 12 byte header. If the queued result carries arguments, e.g. RES_SESSION_ALREADY_OPEN which returns the existing session ID, the second usb_packet_copy() writes past the end of the guest-declared buffer and trips the p->actual_length + bytes <=3D iov->size assertion, aborting QEMU. A guest can control the transfer size freely, e.g. TBYTES in the qTD of an EHCI BULK IN. A device must not send more data than the initiator signaled it would accept. Stall the transfer instead, and keep the result queued so that a subsequent BULK IN with a sufficient buffer size delivers the full response. Fixes: 840a178c94db ("usb: mtp filesharing") Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3386 Signed-off-by: Tommaso Califano Reviewed-by: Junjie Cao Reviewed-by: Luigi Leonardi --- hw/usb/dev-mtp.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/hw/usb/dev-mtp.c b/hw/usb/dev-mtp.c index c2d36a73cf..cbc2be3317 100644 --- a/hw/usb/dev-mtp.c +++ b/hw/usb/dev-mtp.c @@ -1905,6 +1905,13 @@ static void usb_mtp_handle_data(USBDevice *dev, USBP= acket *p) } else if (s->result !=3D NULL) { MTPControl *r =3D s->result; int length =3D sizeof(container) + r->argc * sizeof(uint32_t); + + if (p->iov.size < length) { + trace_usb_mtp_stall(s->dev.addr, + "packet too small to send response"); + p->status =3D USB_RET_STALL; + return; + } if (r->code =3D=3D RES_OK) { trace_usb_mtp_success(s->dev.addr, r->trans, (r->argc > 0) ? r->argv[0] : 0, --=20 2.56.0