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Fri, 13 Jun 2025 04:22:24 -0700 (PDT) From: Cosmin Tanislav To: Cc: Sean Young , Mauro Carvalho Chehab , linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, Cosmin Tanislav Subject: [PATCH v5 3/3] media: rc: ir-spi: avoid overflow in multiplication Date: Fri, 13 Jun 2025 14:21:53 +0300 Message-ID: <20250613112210.22731-4-demonsingur@gmail.com> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250613112210.22731-1-demonsingur@gmail.com> References: <20250613112210.22731-1-demonsingur@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Switch to u64 arithmetic and use DIV_ROUND_CLOSEST_ULL() to avoid the overflow. buffer[i] is unsigned int and is limited by the lirc core to IR_MAX_DURATION, which is 500000. idata->freq is u32, which has a max value of 0xFFFFFFFF. In the case where buffer[i] is 500000, idata->freq overflows the u32 multiplication for any values >=3D 8590. 0xFFFFFFFF / 500000 ~=3D 8589 By casting buffer[i] to u64, idata->freq can be any u32 value without overflowing the multiplication. 0xFFFFFFFFFFFFFFFF / 500000 ~=3D 36893488147419 (> 4294967295) The result of the final operation will fit back into the unsigned int limits without any issues. 500000 * 0xFFFFFFFF / 1000000 =3D 0x80000000 (< 0xFFFFFFFF) Signed-off-by: Cosmin Tanislav --- drivers/media/rc/ir-spi.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/media/rc/ir-spi.c b/drivers/media/rc/ir-spi.c index 0b54ad74cec0..392441e0c116 100644 --- a/drivers/media/rc/ir-spi.c +++ b/drivers/media/rc/ir-spi.c @@ -46,7 +46,8 @@ static int ir_spi_tx(struct rc_dev *dev, unsigned int *bu= ffer, unsigned int coun =20 /* convert the pulse/space signal to raw binary signal */ for (i =3D 0; i < count; i++) { - buffer[i] =3D DIV_ROUND_CLOSEST(buffer[i] * idata->freq, 1000000); + buffer[i] =3D DIV_ROUND_CLOSEST_ULL((u64)buffer[i] * idata->freq, + 1000000); len +=3D buffer[i]; } =20 --=20 2.49.0