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Wed, 04 Nov 2026 15:45:32 -0800 (PST) Received: from google.com ([2a00:79e0:2ebe:8:c8f4:b7d9:252f:4483]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-36ca39972d4sm18076499eec.26.2026.11.04.15.45.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Nov 2026 15:45:31 -0800 (PST) Date: Wed, 4 Nov 2026 15:45:28 -0800 From: Dmitry Torokhov To: Guanglei Zhu Cc: linux-input@vger.kernel.org, linux-kernel@vger.kernel.org, liuc63@xiaopeng.com Subject: Re: [PATCH v3] Input: joydev - avoid signed overflow in the broken-axis correction Message-ID: References: <8063a24bb9f75bb9096c947d8ffa7123@gmail.com> <20261104055058.854710-1-zhugl3@xiaopeng.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261104055058.854710-1-zhugl3@xiaopeng.com> On Wed, Nov 04, 2026 at 01:50:58PM +0800, Guanglei Zhu wrote: > The JS_CORR_BROKEN correction multiplies two 32-bit values taken > from user space via JSIOCSCORR before shifting and clamping: > > value = value > corr->coef[0] ? (value < corr->coef[1] ? 0 : > ((corr->coef[3] * (value - corr->coef[1])) >> 14)) : > ((corr->coef[2] * (value - corr->coef[0])) >> 14); > > Nothing bounds the coefficients, so with large enough values the > products wrap around and the correction returns bogus axis values > for the rest of the session. > > Compute the correction in 64 bits and clamp once, and flatten the > nested ternary so the dead zone returns 0 directly. > > Signed-off-by: Guanglei Zhu Applied, thank you. -- Dmitry