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Wed, 17 Jun 2026 23:37:53 -0700 (PDT) Received: from nugod-NUC15CRHU5.tail9f095a.ts.net ([218.237.104.87]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2c6e54e8257sm13505905ad.16.2026.06.17.23.37.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 17 Jun 2026 23:37:52 -0700 (PDT) From: HyeongJun An To: Benjamin Tissoires , Jiri Kosina Cc: =?UTF-8?q?Filipe=20La=C3=ADns?= , Lee Jones , linux-input@vger.kernel.org, linux-kernel@vger.kernel.org, HyeongJun An , stable@vger.kernel.org Subject: [PATCH] HID: logitech-dj: Fix maxfield check in DJ short report validation Date: Thu, 18 Jun 2026 15:37:37 +0900 Message-ID: <20260618063737.211468-1-sammiee5311@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-input@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Commit b6a57912854e ("HID: logitech-dj: Prevent REPORT_ID_DJ_SHORT related user initiated OOB write") added validation for the DJ short output report, but the error path dereferences rep->field[0] even when rep->maxfield is zero. Commit 8b9a097eb2fc ("HID: logitech-dj: fix wrong detection of bad DJ_SHORT output report") made the check conditional on rep being present, but a crafted descriptor can still create report ID 0x20 with only padding output items. hid-core registers the report, ignores the padding field, and leaves rep->maxfield as zero. In that case the validation enters the rep->maxfield < 1 branch and then dereferences rep->field[0]->report_count while printing the error message, causing a NULL pointer dereference during probe. This is reproducible with uhid by emulating a Logitech receiver with a padding-only DJ short output report: BUG: KASAN: null-ptr-deref in logi_dj_probe+0xb1/0x754 [hid_logitech_dj] Read of size 4 at addr 0000000000000028 by task kworker/4:1/129 ... Call Trace: logi_dj_probe+0xb1/0x754 [hid_logitech_dj] hid_device_probe+0x329/0x3f0 [hid] really_probe+0x162/0x570 __device_attach+0x137/0x2c0 bus_probe_device+0x38/0xc0 device_add+0xa56/0xce0 hid_add_device+0x19c/0x280 [hid] uhid_device_add_worker+0x2c/0xb0 [uhid] Reject the zero-field report before printing the field report_count. Fixes: b6a57912854e ("HID: logitech-dj: Prevent REPORT_ID_DJ_SHORT related user initiated OOB write") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-4-8 Signed-off-by: HyeongJun An --- drivers/hid/hid-logitech-dj.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/drivers/hid/hid-logitech-dj.c b/drivers/hid/hid-logitech-dj.c index 381e4dc5aba7..9c574ab8b60b 100644 --- a/drivers/hid/hid-logitech-dj.c +++ b/drivers/hid/hid-logitech-dj.c @@ -1907,8 +1907,13 @@ static int logi_dj_probe(struct hid_device *hdev, output_report_enum = &hdev->report_enum[HID_OUTPUT_REPORT]; rep = output_report_enum->report_id_hash[REPORT_ID_DJ_SHORT]; - if (rep && (rep->maxfield < 1 || - rep->field[0]->report_count != DJREPORT_SHORT_LENGTH - 1)) { + if (rep && rep->maxfield < 1) { + hid_err(hdev, "Expected size of DJ short report is %d, but got 0", + DJREPORT_SHORT_LENGTH - 1); + return -EINVAL; + } + + if (rep && rep->field[0]->report_count != DJREPORT_SHORT_LENGTH - 1) { hid_err(hdev, "Expected size of DJ short report is %d, but got %d", DJREPORT_SHORT_LENGTH - 1, rep->field[0]->report_count); return -EINVAL; -- 2.43.0