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Tue, 22 Jul 2025 04:19:04 -0700 (PDT) Received: from gmail.com ([2a02:c7c:f4f0:900:2e21:a766:f429:7a71]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b61ca2c013sm13179175f8f.33.2025.07.22.04.19.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 22 Jul 2025 04:19:03 -0700 (PDT) Date: Tue, 22 Jul 2025 12:19:01 +0100 From: Qasim Ijaz To: Jiri Slaby Cc: jikos@kernel.org, bentiss@kernel.org, linux-input@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Dmitry Savin Subject: Re: [PATCH RESEND] HID: multitouch: fix slab out-of-bounds access in mt_report_fixup() Message-ID: References: <20250722080003.3605-1-qasdev00@gmail.com> Precedence: bulk X-Mailing-List: linux-input@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, Jul 22, 2025 at 11:16:15AM +0200, Jiri Slaby wrote: > On 22. 07. 25, 10:00, Qasim Ijaz wrote: > > A malicious HID device can trigger a slab out-of-bounds during > > mt_report_fixup() by passing in report descriptor smaller than > > 607 bytes. mt_report_fixup() attempts to patch byte offset 607 > > of the descriptor with 0x25 by first checking if byte offset > > 607 is 0x15 however it lacks bounds checks to verify if the > > descriptor is big enough before conducting this check. Fix > > this vulnerability by ensuring the descriptor size is > > greater than or equal to 608 before accessing it. > > > > Below is the KASAN splat after the out of bounds access happens: > > > > [ 13.671954] ================================================================== > > [ 13.672667] BUG: KASAN: slab-out-of-bounds in mt_report_fixup+0x103/0x110 > > [ 13.673297] Read of size 1 at addr ffff888103df39df by task kworker/0:1/10 > > [ 13.673297] > > [ 13.673297] CPU: 0 UID: 0 PID: 10 Comm: kworker/0:1 Not tainted 6.15.0-00005-gec5d573d83f4-dirty #3 > > [ 13.673297] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/04 > > [ 13.673297] Call Trace: > > [ 13.673297] > > [ 13.673297] dump_stack_lvl+0x5f/0x80 > > [ 13.673297] print_report+0xd1/0x660 > > [ 13.673297] kasan_report+0xe5/0x120 > > [ 13.673297] __asan_report_load1_noabort+0x18/0x20 > > [ 13.673297] mt_report_fixup+0x103/0x110 > > [ 13.673297] hid_open_report+0x1ef/0x810 > > [ 13.673297] mt_probe+0x422/0x960 > > [ 13.673297] hid_device_probe+0x2e2/0x6f0 > > [ 13.673297] really_probe+0x1c6/0x6b0 > > [ 13.673297] __driver_probe_device+0x24f/0x310 > > [ 13.673297] driver_probe_device+0x4e/0x220 > > [ 13.673297] __device_attach_driver+0x169/0x320 > > [ 13.673297] bus_for_each_drv+0x11d/0x1b0 > > [ 13.673297] __device_attach+0x1b8/0x3e0 > > [ 13.673297] device_initial_probe+0x12/0x20 > > [ 13.673297] bus_probe_device+0x13d/0x180 > > [ 13.673297] device_add+0xe3a/0x1670 > > [ 13.673297] hid_add_device+0x31d/0xa40 > > [...] > > > > Fixes: c8000deb6836 ("HID: multitouch: Add support for GT7868Q") > > Cc: stable@vger.kernel.org > > Signed-off-by: Qasim Ijaz > > Reviewed-by: Dmitry Savin > > --- > > drivers/hid/hid-multitouch.c | 25 ++++++++++++++++--------- > > 1 file changed, 16 insertions(+), 9 deletions(-) > > > > diff --git a/drivers/hid/hid-multitouch.c b/drivers/hid/hid-multitouch.c > > index 7ac8e16e6158..af4abe3ba410 100644 > > --- a/drivers/hid/hid-multitouch.c > > +++ b/drivers/hid/hid-multitouch.c > > @@ -1461,18 +1461,25 @@ static const __u8 *mt_report_fixup(struct hid_device *hdev, __u8 *rdesc, > > if (hdev->vendor == I2C_VENDOR_ID_GOODIX && > > (hdev->product == I2C_DEVICE_ID_GOODIX_01E8 || > > hdev->product == I2C_DEVICE_ID_GOODIX_01E9)) { > > - if (rdesc[607] == 0x15) { > > - rdesc[607] = 0x25; > > - dev_info( > > - &hdev->dev, > > - "GT7868Q report descriptor fixup is applied.\n"); > > + if (*size >= 608) { > > + if (rdesc[607] == 0x15) { > > + rdesc[607] = 0x25; > > + dev_info( > > + &hdev->dev, > > + "GT7868Q report descriptor fixup is applied.\n"); > > + } else { > > + dev_info( > > + &hdev->dev, > > + "The byte is not expected for fixing the report descriptor. \ > > + It's possible that the touchpad firmware is not suitable for applying the fix. \ > > + got: %x\n", > > This is wrong. You have all the spaces/tabs in the string now. Drop all the > backslashes, and open and close the string on every line. > > > + rdesc[607]); > > + } > > As this is superlong and superindented, perhaps introduce a new function for > these devices? > > > } else { > > dev_info( > > &hdev->dev, > > - "The byte is not expected for fixing the report descriptor. \ > > -It's possible that the touchpad firmware is not suitable for applying the fix. \ > > -got: %x\n", > > This was horrid too, yeah. > > > - rdesc[607]); > > + "GT7868Q fixup: report descriptor only %u bytes, skipping\n", > > A predicate missing. Eg. "has only", or "is only". > Thanks for the feedback Jiri, I took the advice on board, is something like this better? static const __u8 *mt_report_fixup(struct hid_device *hdev, __u8 *rdesc, unsigned int *size) { if (hdev->vendor == I2C_VENDOR_ID_GOODIX && (hdev->product == I2C_DEVICE_ID_GOODIX_01E8 || hdev->product == I2C_DEVICE_ID_GOODIX_01E9)) { if (*size < 608) { dev_info( &hdev->dev, "GT7868Q fixup: report descriptor is only %u bytes, skipping\n", *size); return rdesc; } if (rdesc[607] == 0x15) { rdesc[607] = 0x25; dev_info( &hdev->dev, "GT7868Q fixup: report descriptor fixup is applied.\n"); } else { dev_info(&hdev->dev, "GT7868Q fixup: offset 607 is %x (expected 0x15), " "descriptor may be malformed, skipping\n", rdesc[607]); } } return rdesc; } the key changes I made are: - Move size check to the top, this way the indentation level is decent - get rid of message backslashes - shorten the fixup failure message when rdesc[607] is not 0x15 and make it a bit clearer since this message was the longest - just a minor cleanup - added "is only %u bytes" as you suggested if this is all good I can send v2. Thanks qasim > > + *size); > > } > > } > > thanks, > -- > js > suse labs >