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Thu, 24 Sep 2026 07:14:25 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id oTP2LtHNtGoqCQAAD6G6ig (envelope-from ); Thu, 24 Sep 2026 07:14:25 +0000 Message-ID: <35bc19a3-27d7-4d3e-978e-0692de78f8a0@suse.de> Date: Thu, 24 Sep 2026 09:14:25 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/2] drm/udl: reject short USB control transfers in udl_read_edid_block() To: Hui Peng , jani.nikula@linux.intel.com, 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 References: <20260919223511.3889061-1-benquike@gmail.com> <20260924064434.2541959-1-benquike@gmail.com> <20260924064434.2541959-2-benquike@gmail.com> Content-Language: en-US From: Thomas Zimmermann Autocrypt: addr=tzimmermann@suse.de; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Score: -4.30 X-Spam-Level: X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-0.999]; MIME_GOOD(-0.10)[text/plain]; FREEMAIL_TO(0.00)[gmail.com,linux.intel.com,kernel.org,ffwll.ch]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; RCPT_COUNT_SEVEN(0.00)[9]; MIME_TRACE(0.00)[0:+]; MID_RHS_MATCH_FROM(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; RCVD_TLS_ALL(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,suse.de:mid,suse.com:url] X-Spam-Flag: NO Hi Am 24.09.26 um 08:44 schrieb Hui Peng: > 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 > Assisted-by: LLM > Signed-off-by: Hui Peng > --- > 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..b7c462436573 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) { Please test for (ret < 2) instead. It makes the test a little less dependent on the earlier calls. Best regards Thomas > ret = -EIO; > drm_err(dev, "Read EDID byte %zu failed\n", i); > goto err_drm_dev_exit; -- -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com GF: Stefan Gaiser, Jochen Jaser, Abhinav Puri, (HRB 36809, AG Nürnberg)