A buffer overflow vulnerability exists in the USB 9pfs transport layer where inconsistent size validation between packet header parsing and actual data copying allows a malicious USB host to overflow heap buffers.

The issue occurs because: - usb9pfs_rx_header() validates only the declared size in packet header - usb9pfs_rx_complete() uses req->actual (actual received bytes) for memcpy

This allows an attacker to craft packets with small declared size (bypassing validation) but large actual payload (triggering overflow in memcpy).

Add validation in usb9pfs_rx_complete() to ensure req->actual does not exceed the buffer capacity before copying data.

Reported-by: Yuhao Jiang danisjiang@gmail.com Fixes: a3be076dc174 ("net/9p/usbg: Add new usb gadget function transport") Cc: stable@vger.kernel.org Signed-off-by: Yuhao Jiang danisjiang@gmail.com --- net/9p/trans_usbg.c | 9 +++++++++ 1 file changed, 9 insertions(+)

diff --git a/net/9p/trans_usbg.c b/net/9p/trans_usbg.c index 6b694f117aef..047a2862fc84 100644 --- a/net/9p/trans_usbg.c +++ b/net/9p/trans_usbg.c @@ -242,6 +242,15 @@ static void usb9pfs_rx_complete(struct usb_ep *ep, struct usb_request *req) if (!p9_rx_req) return;

+ /* Validate actual received size against buffer capacity */ + if (req->actual > p9_rx_req->rc.capacity) { + dev_err(&cdev->gadget->dev, + "received data size %u exceeds buffer capacity %zu\n", + req->actual, p9_rx_req->rc.capacity); + p9_req_put(usb9pfs->client, p9_rx_req); + return; + } + memcpy(p9_rx_req->rc.sdata, req->buf, req->actual);

p9_rx_req->rc.size = req->actual;