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Tue, 03 Nov 2026 10:45:23 -0800 (PST) Received: from google.com ([2a00:79e0:2ebe:8:88b4:22ec:d621:c1b]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-36ca3788bffsm102648eec.1.2026.11.03.10.45.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 03 Nov 2026 10:45:22 -0800 (PST) Date: Tue, 3 Nov 2026 10:45:18 -0800 From: Dmitry Torokhov To: Guanglei Zhu Cc: linux-input@vger.kernel.org, linux-kernel@vger.kernel.org, liuc63@xiaopeng.com, stable@vger.kernel.org Subject: Re: [PATCH] Input: joydev - avoid an undefined shift in the legacy 0x read Message-ID: References: <20261103084135.426629-1-zhugl3@xiaopeng.com> X-Mailing-List: linux-input@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: <20261103084135.426629-1-zhugl3@xiaopeng.com> Hi Guanglei, On Tue, Nov 03, 2026 at 04:41:28PM +0800, Guanglei Zhu wrote: > The legacy 0.x read path shifts the axis values by the calibration > constants that JS_SET_CAL installs: > > data.x = (joydev->abs[0] / 256 + 128) >> joydev->glue.JS_CORR.x; > data.y = (joydev->abs[1] / 256 + 128) >> joydev->glue.JS_CORR.y; > > JS_CORR is copied straight from userspace as three s32 values and > never validated, so the shift count can be negative or wider than > the type, which is undefined behavior: the shift compiles to > whatever the architecture does with an out-of-range count, and the > compiler is free to assume it cannot happen. > > Clamp the shift count to the width of the shifted value. > > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") > Cc: stable@vger.kernel.org Why do all these need to be in stable? > Signed-off-by: Guanglei Zhu > --- > drivers/input/joydev.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/input/joydev.c b/drivers/input/joydev.c > index 32459fd8a7c1..4740099599bf 100644 > --- a/drivers/input/joydev.c > +++ b/drivers/input/joydev.c > @@ -353,8 +353,8 @@ static ssize_t joydev_0x_read(struct joydev_client *client, > for (data.buttons = i = 0; i < 32 && i < joydev->nkey; i++) > data.buttons |= > test_bit(joydev->keypam[i], input->key) ? (1 << i) : 0; > - data.x = (joydev->abs[0] / 256 + 128) >> joydev->glue.JS_CORR.x; > - data.y = (joydev->abs[1] / 256 + 128) >> joydev->glue.JS_CORR.y; > + data.x = (joydev->abs[0] / 256 + 128) >> clamp(joydev->glue.JS_CORR.x, 0, 31); > + data.y = (joydev->abs[1] / 256 + 128) >> clamp(joydev->glue.JS_CORR.y, 0, 31); > > /* > * Reset reader's event queue Thanks. -- Dmitry