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[34.127.51.67]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3a0972efa0bsm3184726a91.8.2026.09.24.00.30.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 24 Sep 2026 00:30:14 -0700 (PDT) From: Hui Peng To: jani.nikula@linux.intel.com, tzimmermann@suse.de, maarten.lankhorst@linux.intel.com, mripard@kernel.org, airlied@gmail.com, simona@ffwll.ch Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Hui Peng Subject: [PATCH v3 1/2] drm/udl: reject short USB control transfers in udl_read_edid_block() Date: Thu, 24 Sep 2026 07:30:10 +0000 Message-ID: <20260924073012.2742968-2-benquike@gmail.com> X-Mailer: git-send-email 2.56.0.rc1.310.g51773c2048-goog In-Reply-To: <20260924064434.2541959-2-benquike@gmail.com> References: <20260924064434.2541959-1-benquike@gmail.com> <20260924064434.2541959-2-benquike@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Mailman-Approved-At: Fri, 25 Sep 2026 07:30:44 +0000 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" In udl_read_edid_block(), usb_control_msg() requests 2 bytes into read_buff for each EDID byte, and read_buff[1] is stored into buf[i]. Currently the short-transfer check tests ret < 1 instead of ret < 2, so if a short USB control transfer returns 1 byte, read_buff[1] is not written by usb_control_msg() and retains the previous iteration's byte (or uninitialized kmalloc(2) memory on the first iteration), which is then copied into buf[i]. Change the check from ret < 1 to ret < 2 so any short USB control transfer fails with -EIO. Tested in QEMU against Linux 7.3.0-rc3 using dummy_hcd and raw-gadget emulating a DisplayLink UDL USB device: on the unfixed kernel, when usb_control_msg() returned 1 byte for an EDID read (short transfer), udl_read_edid_block() accepted ret = 1 and stored stale read_buff[1] data into the EDID buffer; whereas with this fix applied, ret < 2 correctly fails with -EIO and prevents EDID buffer corruption. Fixes: 5320918b9a87 ("drm/udl: initial UDL driver (v4)") Cc: stable@vger.kernel.org Reviewed-by: Thomas Zimmermann Assisted-by: LLM Signed-off-by: Hui Peng --- Changes in v3: - Change (ret != 2) to (ret < 2) in udl_read_edid_block(), as requested by Thomas Zimmermann. Changes in v2: - Split out as patch 1/2 as requested by Jani Nikula. - Added testing details in QEMU on short USB EDID control transfers. drivers/gpu/drm/udl/udl_edid.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/gpu/drm/udl/udl_edid.c b/drivers/gpu/drm/udl/udl_edid.c index af4cff2a7c51..2120e363b6eb 100644 --- a/drivers/gpu/drm/udl/udl_edid.c +++ b/drivers/gpu/drm/udl/udl_edid.c @@ -36,7 +36,7 @@ static int udl_read_edid_block(void *data, u8 *buf, unsigned int block, size_t l if (ret < 0) { drm_err(dev, "Read EDID byte %zu failed err %x\n", i, ret); goto err_drm_dev_exit; - } else if (ret < 1) { + } else if (ret < 2) { ret = -EIO; drm_err(dev, "Read EDID byte %zu failed\n", i); goto err_drm_dev_exit; -- 2.55.0.1082.g2b9226bbc0-goog