From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailgw.kylinos.cn (mailgw.kylinos.cn [124.126.103.232]) (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 1A65F46AF31; Mon, 24 Aug 2026 17:04:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=124.126.103.232 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787591100; cv=none; b=o/uC7y9UCg8DPMt1AePLvYOmTMR6FUDmNqev82VZqdErGQWE23ERKqnm5XSVOb/xK+S4I0ecpwrMS9h1Ca/im2nAOM5FPOqAA4Ozx5uX6O+sE612ivq4GgTG1bR9WiJgNgfjux6YYVdf4G1tvFCcyn1rQ7km9sFB56Z8TLD8ngI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787591100; c=relaxed/simple; bh=G/me3LHfBUuzpn2DDkF7CZaGgU2p7vjA8yk8hft6mm0=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=H9SWccpks3eE06/96T1pLxMMZ1bZMIUZzzenkwUfye80y66WQwwqUbEl2107/4fJ5pXzVKR9MsU5dlXadm/Yx6hKSy53utTQNpqNA7rlm0emvLLoANp6CtHd3vXeILJYlTYddblvBx2J7NOFnZ1z4340TsASWmjJ2UQmPHDygxE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=kylinos.cn; spf=pass smtp.mailfrom=kylinos.cn; arc=none smtp.client-ip=124.126.103.232 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=kylinos.cn Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=kylinos.cn X-UUID: e92555309fdd11f19a56ed5b684f684d-20260825 X-CID-P-RULE: Release_Ham X-CID-O-INFO: VERSION:1.3.19,REQID:727308e7-413a-4a32-bcb2-60a8cca12529,IP:0,U RL:0,TC:0,Content:0,EDM:25,RT:0,SF:0,FILE:0,BULK:0,RULE:Release_Ham,ACTION :release,TS:25 X-CID-META: VersionHash:7db8b62,CLOUDID:ad2fbeabeed0f4ca0759e012c658d90c,BulkI D:nil,BulkQuantity:0,SF:81|82|102|850|865|898,TC:nil,Content:0|15|50,EDM:5 ,IP:nil,URL:0,File:nil,RT:nil,Bulk:nil,QS:nil,BEC:nil,COL:0,OSI:0,OSA:0,AV :0,LES:1,SPR:NO,DKR:0,DKP:0,BRR:0,BRE:0,ARC:0 X-CID-BVR: 2,SSN|SDN X-CID-BAS: 2,SSN|SDN,0,_ X-CID-FACTOR: TF_CID_SPAM_SNR X-CID-RHF: D41D8CD98F00B204E9800998ECF8427E X-UUID: e92555309fdd11f19a56ed5b684f684d-20260825 X-User: lihaofeng@kylinos.cn Received: from localhost.localdomain [(10.44.16.150)] by mailgw.kylinos.cn (envelope-from ) (Generic MTA with TLSv1.3 TLS_AES_256_GCM_SHA384 256/256) with ESMTP id 152646855; Tue, 25 Aug 2026 01:04:47 +0800 From: Haofeng Li To: gregkh@linuxfoundation.org, linux-usb@vger.kernel.org Cc: dan.scally@ideasonboard.com, andriy.shevchenko@intel.com, xu.yang_2@nxp.com, hhhuuu@google.com, kees@kernel.org, kai.aizen.dev@gmail.com, rdunlap@infradead.org, christophe.jaillet@wanadoo.fr, linux-kernel@vger.kernel.org, 13266079573@163.com, Haofeng Li Subject: [PATCH v4] usb: gadget: f_uvc: fix Extension Unit descriptor heap overflow Date: Tue, 25 Aug 2026 01:04:42 +0800 Message-Id: <20260824170442.1980191-1-lihaofeng@kylinos.cn> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20260824094456.1562456-1-lihaofeng@kylinos.cn> References: <20260824094456.1562456-1-lihaofeng@kylinos.cn> Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit An Extension Unit descriptor is 24 + bNrInPins + bControlSize bytes long (UVC_DT_EXTENSION_UNIT_SIZE(p, n)), where bNrInPins and bControlSize are configfs attributes each accepted over the full 0..255 range by kstrtou8(). uvc_configfs stores the computed size in the u8 bLength field of the descriptor, so once 24 + p + n exceeds 255 it silently wraps: p = n = 255 describes a 534-byte descriptor with bLength = 22. uvc_copy_descriptors() reserves xu->desc.bLength bytes per Extension Unit in the descriptor buffer it allocates at bind time, but UVC_COPY_XU_DESCRIPTOR() copies the real descriptor contents, i.e. 22 + bNrInPins + 1 + bControlSize + 1 bytes. With the wrapped length the copy overruns the allocation by up to 512 bytes. Attack chain (write access to a UVC gadget's configfs attributes; no race, no USB traffic, a single bind triggers it): echo 255 > .../functions/uvc.0/extensions/ext.0/b_nr_in_pins echo 255 > .../functions/uvc.0/extensions/ext.0/b_control_size -> uvcg_extension_b_nr_in_pins_store() / uvcg_extension_b_control_size_store() -> bLength = UVC_DT_EXTENSION_UNIT_SIZE(255, 255) wraps to 22 bind the gadget to a UDC -> uvc_function_bind() -> uvc_copy_descriptors() -> kmalloc() sized using the wrapped bLength: 22 bytes for the XU -> UVC_COPY_XU_DESCRIPTOR() writes the real 534 bytes into that slot (22-byte head, 255 baSourceID, bControlSize, 255 bmControls, iExtension) -> heap out-of-bounds write during bind Reproduced on 7.2.0+: a stock build (FORTIFY on) can derive the remaining allocation size at the bmControls memcpy and BUGs in __fortify_panic() during bind - a deterministic kernel crash; with FORTIFY disabled for the file, KASAN reports "slab-out-of-bounds Write of size 255" in uvc_copy_descriptors() against the kmalloc-192 descriptor buffer. Reject combinations whose descriptor does not fit into bLength at all four configfs entry points that can grow an Extension Unit (b_nr_in_pins, b_control_size, ba_source_id, bm_controls), and make uvc_copy_descriptors() refuse an Extension Unit whose bLength does not match its contents instead of overflowing the buffer. Fixes: 0525210c9840 ("usb: gadget: uvc: Allow definition of XUs in configfs") Signed-off-by: Haofeng Li Assisted-by: opencode:deepseek-v4-flash-free Reviewed-by: Daniel Scally --- Changes in v2: - reword a comment per Randy Dunlap: "The descriptor length must fit into the one-byte bLength field". Changes in v3: - Add a warning message when the descriptor size is rejected, as suggested by Dan Scally. Changes in v4: - Remove the blank line inside the sign-off block. drivers/usb/gadget/function/f_uvc.c | 6 +++++ drivers/usb/gadget/function/uvc_configfs.c | 28 ++++++++++++++++++++++ 2 files changed, 34 insertions(+) diff --git a/drivers/usb/gadget/function/f_uvc.c b/drivers/usb/gadget/function/f_uvc.c index 73dc7e42875f..0d3432f80cae 100644 --- a/drivers/usb/gadget/function/f_uvc.c +++ b/drivers/usb/gadget/function/f_uvc.c @@ -598,6 +598,12 @@ uvc_copy_descriptors(struct uvc_device *uvc, enum usb_device_speed speed) } list_for_each_entry(xu, uvc->desc.extension_units, list) { + /* Mismatched bLength would overflow the buffer sized after it */ + if (xu->desc.bLength != + UVC_DT_EXTENSION_UNIT_SIZE(xu->desc.bNrInPins, + xu->desc.bControlSize)) + return ERR_PTR(-EINVAL); + control_size += xu->desc.bLength; bytes += xu->desc.bLength; n_desc++; diff --git a/drivers/usb/gadget/function/uvc_configfs.c b/drivers/usb/gadget/function/uvc_configfs.c index 70a1415ea401..b52c9cf2b715 100644 --- a/drivers/usb/gadget/function/uvc_configfs.c +++ b/drivers/usb/gadget/function/uvc_configfs.c @@ -845,6 +845,18 @@ static ssize_t uvcg_extension_b_num_controls_store(struct config_item *item, } UVCG_EXTENSION_ATTR(b_num_controls, bNumControls); +/* The descriptor length must fit into the one-byte bLength field */ +static int uvcg_extension_check_size(u8 nr_in_pins, u8 control_size) +{ + if (UVC_DT_EXTENSION_UNIT_SIZE(nr_in_pins, control_size) > 255) { + pr_warn("uvc: Extension Unit descriptor size (%u + %u) does not fit into bLength\n", + nr_in_pins, control_size); + return -EINVAL; + } + + return 0; +} + /* * In addition to storing bNrInPins, this function needs to realloc the * memory for the baSourceID array and additionally expand bLength. @@ -877,6 +889,10 @@ static ssize_t uvcg_extension_b_nr_in_pins_store(struct config_item *item, goto unlock; } + ret = uvcg_extension_check_size(num, xu->desc.bControlSize); + if (ret) + goto unlock; + tmp_buf = krealloc_array(xu->desc.baSourceID, num, sizeof(u8), GFP_KERNEL | __GFP_ZERO); if (!tmp_buf) { @@ -930,6 +946,10 @@ static ssize_t uvcg_extension_b_control_size_store(struct config_item *item, goto unlock; } + ret = uvcg_extension_check_size(xu->desc.bNrInPins, num); + if (ret) + goto unlock; + tmp_buf = krealloc_array(xu->desc.bmControls, num, sizeof(u8), GFP_KERNEL | __GFP_ZERO); if (!tmp_buf) { @@ -1055,6 +1075,10 @@ static ssize_t uvcg_extension_ba_source_id_store(struct config_item *item, if (ret) goto unlock; + ret = uvcg_extension_check_size(n, xu->desc.bControlSize); + if (ret) + goto unlock; + iter = source_ids = kcalloc(n, sizeof(u8), GFP_KERNEL); if (!source_ids) { ret = -ENOMEM; @@ -1134,6 +1158,10 @@ static ssize_t uvcg_extension_bm_controls_store(struct config_item *item, if (ret) goto unlock; + ret = uvcg_extension_check_size(xu->desc.bNrInPins, n); + if (ret) + goto unlock; + iter = bm_controls = kcalloc(n, sizeof(u8), GFP_KERNEL); if (!bm_controls) { ret = -ENOMEM; -- 2.25.1