From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 13DDFB67E; Wed, 8 Apr 2026 18:38:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775673483; cv=none; b=pn2BXn5LNL/KbdOCz5b5ml/C/fEvvE7+fyjQecinsHGEy9jAy8kWgoz8KBv1Ji+5N7HAFrLVqetHx3L6dFuOgu+qPVWUj7npRDA+H2E3XKnf875wTEsWzCuL3e3QH2nPEKUNt8m8J46mBhCg+tNfjlLOzwOE5ldxAnmDSF6+C+U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775673483; c=relaxed/simple; bh=TuybkVLMOFNtVutZZBMSYUQW4G/v1ix8XzupsR5KB2g=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=GzqomxYCO3q2ks1wvcjST+pKq/hDv0ip2jZ93Du8NGoBgTr4TLUIhpEkVmXKyOslOgMqz1U6kauCcGS+YGFd4gfVGzu6qMZQf7hQvBzJ38qxi/h2bHB8DARgiKITx7Y0vHeBTWDJsG0JIzzUYgngzqvO8fSCNifR5/KGBZpYFPQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=GTxlzg+L; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="GTxlzg+L" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9D657C19421; Wed, 8 Apr 2026 18:38:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1775673483; bh=TuybkVLMOFNtVutZZBMSYUQW4G/v1ix8XzupsR5KB2g=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=GTxlzg+L44jBuB/Z8QwcO5YqEpaKzeKqRZRT68A61GGke9KruYp36WpkUoeClfI3v /y+oa7trn5BDaK+aZKyPK9o8KfjguaL1+AFWZlwVkcQgs7vtApH5MNPaCaSrTUb77I TB4I1aUj/B57/0vZCoxevutIg/xKzpuCMpt/X/ss= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Sebastian Urban , stable , Alan Stern Subject: [PATCH 6.18 248/277] usb: gadget: dummy_hcd: fix premature URB completion when ZLP follows partial transfer Date: Wed, 8 Apr 2026 20:03:53 +0200 Message-ID: <20260408175943.119447317@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260408175933.836769063@linuxfoundation.org> References: <20260408175933.836769063@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Sebastian Urban commit f50200dd44125e445a6164e88c217472fa79cdbc upstream. When a gadget request is only partially transferred in transfer() because the per-frame bandwidth budget is exhausted, the loop advances to the next queued request. If that next request is a zero-length packet (ZLP), len evaluates to zero and the code takes the unlikely(len == 0) path, which sets is_short = 1. This bypasses the bandwidth guard ("limit < ep->ep.maxpacket && limit < len") that lives in the else branch and would otherwise break out of the loop for non-zero requests. The is_short path then completes the URB before all data from the first request has been transferred. Reproducer (bulk IN, high speed): Device side (FunctionFS with Linux AIO): 1. Queue a 65024-byte write via io_submit (127 * 512, i.e. a multiple of the HS bulk max packet size). 2. Immediately queue a zero-length write (ZLP) via io_submit. Host side: 3. Submit a 65536-byte bulk IN URB. Expected: URB completes with actual_length = 65024. Actual: URB completes with actual_length = 53248, losing 11776 bytes that leak into subsequent URBs. At high speed the per-frame budget is 53248 bytes (512 * 13 * 8). The 65024-byte request exhausts this budget after 53248 bytes, leaving the request incomplete (req->req.actual < req->req.length). Neither the request nor the URB is finished, and rescan is 0, so the loop advances to the ZLP. For the ZLP, dev_len = 0, so len = min(12288, 0) = 0, taking the unlikely(len == 0) path and setting is_short = 1. The is_short handler then sets *status = 0, completing the URB with only 53248 of the expected 65024 bytes. Fix this by breaking out of the loop when the current request has remaining data (req->req.actual < req->req.length). The request resumes on the next timer tick, preserving correct data ordering. Signed-off-by: Sebastian Urban Cc: stable Reviewed-by: Alan Stern Link: https://patch.msgid.link/20260315151045.1155850-1-surban@surban.net Signed-off-by: Greg Kroah-Hartman --- drivers/usb/gadget/udc/dummy_hcd.c | 6 ++++++ 1 file changed, 6 insertions(+) --- a/drivers/usb/gadget/udc/dummy_hcd.c +++ b/drivers/usb/gadget/udc/dummy_hcd.c @@ -1538,6 +1538,12 @@ top: /* rescan to continue with any other queued i/o */ if (rescan) goto top; + + /* request not fully transferred; stop iterating to + * preserve data ordering across queued requests. + */ + if (req->req.actual < req->req.length) + break; } return sent; }