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Tue, 23 Mar 2021 13:29:17 +0000 Subject: Re: [PATCH] Input: analog - fix invalid snprintf() call To: Arnd Bergmann , Dmitry Torokhov Cc: Arnd Bergmann , Zhang Qilong , linux-input@vger.kernel.org, linux-kernel@vger.kernel.org References: <20210323131456.2600132-1-arnd@kernel.org> From: Rasmus Villemoes Message-ID: Date: Tue, 23 Mar 2021 14:29:15 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 In-Reply-To: <20210323131456.2600132-1-arnd@kernel.org> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [80.208.71.248] X-ClientProxiedBy: AM0PR02CA0194.eurprd02.prod.outlook.com (2603:10a6:20b:28e::31) To AM0PR10MB1874.EURPRD10.PROD.OUTLOOK.COM (2603:10a6:208:3f::10) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [192.168.1.149] (80.208.71.248) by AM0PR02CA0194.eurprd02.prod.outlook.com (2603:10a6:20b:28e::31) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3955.18 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: =?Windows-1252?Q?DZncI9Ij4EJZWsJcM1aWhnqDthDYFtpNluyiCyOfLEFjaneP4lXca9BZ?= =?Windows-1252?Q?upCBygz1Fis06YrFC8cxk7AKU2fJlvbVhTC+V1apCmJPhbbmVEtJxzuN?= =?Windows-1252?Q?oSWhn4/+7yP3SVF/m3v049FWsOv6BR8fKxcOz5Ws8sJx1bFdCvQbe0j7?= =?Windows-1252?Q?0bwPxcIOYB6xtK2XLlHYp//z1Xc2fHjyOvzS44AdJO1F49uc1pN3UTK0?= =?Windows-1252?Q?arxYRpZna+3/IpmiQenS3gSl7F+N5va9fRTRuGibDDbrt03o0t6/JqKY?= =?Windows-1252?Q?FYPNCkdfFRT6wgzTuoAPVrK2NCtHI4XuP3+2zHgO1u2H2KPnVCfZTTsv?= =?Windows-1252?Q?x+g+vg73cBHLJZaAp0FZ1zWrTf+jaEmZvL/2zqaAjzNTQpt56Ki2HYBo?= =?Windows-1252?Q?pvmaOKVf85LUF/GkhomIh3UMipommyUkcu2dcKNMH5iP5aOBfDZjR7C5?= =?Windows-1252?Q?olffVifwrdhlsseMHzzNblOW3LgiqxXVTKkFV5Eb8ts4lReWzpW+xkWv?= =?Windows-1252?Q?2LImYsLJnlTo/TiGHRDCu4hVMPdn9r2ltoBbrJSBBJa90AD8oLhVufCu?= =?Windows-1252?Q?UfoJS3cM3aD5k3FibEJ3F89sMfCgZil1NH5Xqwc6hIjcjkETtEkU0CJm?= =?Windows-1252?Q?wR3uDXrw8lm4THj6SHSSTaPFijCFL12d6KDTjO77vg6rS37VOIjVjrX3?= =?Windows-1252?Q?ul6vmImaKk/bbVHS8eeJqv8KWv+Y6DSwglEpSWhaKuyZmCR3O/66CXRN?= =?Windows-1252?Q?CxcWpvrZ5MPbc0nxsSi7qCzx3x/HZZXo0AQetxP8xlVAp96gmr+2sbEJ?= =?Windows-1252?Q?6E4gbhmYaxoIR5H2lCq7Qz05y12ee9syq1CP2OBQRKrn5QP6NZ+/jeYE?= =?Windows-1252?Q?Y5CwJLY1+SeYykt75GFwRa+BahQT7mxepRyd1Yd8cJ5FZfwxNGh1fBdu?= =?Windows-1252?Q?/FWm9OmehA7kMggLyGufkqM43mTbrer1thGNhpkVdAX7/hSRjdBpUwMP?= =?Windows-1252?Q?dCai1hTYb0iwkuxQdPQ6R49li+7xdpHfXKYpwlGEFTFR0fx6IsTPTtV7?= =?Windows-1252?Q?/c9VTCYdj3zMvt8jr/6rmcpFlLXl+ZqSslMuCcY4sv+PkRc+E8Ujs6tB?= =?Windows-1252?Q?/LXE8rtzNAf01gb8/ejZWH6Cn8nxFF1Q05VngYyiNVZFBv7VHOspeUPz?= =?Windows-1252?Q?zDSzfj7OqyvasPzPGghltNFIGlmQdOAc9f39YZ/SLLzkIzhXA2aOuRCN?= =?Windows-1252?Q?sVWvC1FuA5Wf+qdFNwTN6CzMMo11lZhgcHakY8UxA8KJ3vQvKXBw9A4I?= =?Windows-1252?Q?9GkIdFGT3gg9xI9LgfX4kIKL4UwdXOmE9j2TxnEhUr39NrQ8Ojin7bcx?= =?Windows-1252?Q?q+poSKUaFJw/0sFhS9H/6qRj1RhDMFQwhoyfbb7geIO8KKetjanbC8Tq?= X-OriginatorOrg: prevas.dk X-MS-Exchange-CrossTenant-Network-Message-Id: d3cfbbbc-458a-4a54-6bbd-08d8edffa846 X-MS-Exchange-CrossTenant-AuthSource: AM0PR10MB1874.EURPRD10.PROD.OUTLOOK.COM X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 23 Mar 2021 13:29:17.1194 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: d350cf71-778d-4780-88f5-071a4cb1ed61 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: fvTsPu1j6HKBytqcWHKMs7De/WIfQXFnabHGI4rvoewWFw6fOpLHRYltCfX76IE1kuMHLWiFf6AlpCoTRr8J9qpDqk9Tyu8q5ulk5ZcaJjs= X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM8PR10MB4644 Precedence: bulk List-ID: X-Mailing-List: linux-input@vger.kernel.org On 23/03/2021 14.14, Arnd Bergmann wrote: > From: Arnd Bergmann > > overlapping input and output arguments to snprintf() are > undefined behavior in C99: > Good luck: https://lore.kernel.org/lkml/1457469654-17059-1-git-send-email-linux@rasmusvillemoes.dk/ At least 5 years ago the consensus from old-timers was that "the kernel's snprintf supports this use case, just keep it working that way". > diff --git a/drivers/input/joystick/analog.c b/drivers/input/joystick/analog.c > index f798922a4598..8c9fed3f13e2 100644 > --- a/drivers/input/joystick/analog.c > +++ b/drivers/input/joystick/analog.c > @@ -419,14 +419,16 @@ static void analog_calibrate_timer(struct analog_port *port) > > static void analog_name(struct analog *analog) > { > - snprintf(analog->name, sizeof(analog->name), "Analog %d-axis %d-button", > + int len; > + > + len = snprintf(analog->name, sizeof(analog->name), "Analog %d-axis %d-button", > hweight8(analog->mask & ANALOG_AXES_STD), > hweight8(analog->mask & ANALOG_BTNS_STD) + !!(analog->mask & ANALOG_BTNS_CHF) * 2 + > hweight16(analog->mask & ANALOG_BTNS_GAMEPAD) + !!(analog->mask & ANALOG_HBTN_CHF) * 4); > > if (analog->mask & ANALOG_HATS_ALL) > - snprintf(analog->name, sizeof(analog->name), "%s %d-hat", > - analog->name, hweight16(analog->mask & ANALOG_HATS_ALL)); > + len += snprintf(analog->name + len, sizeof(analog->name) - len, "%d-hat", > + hweight16(analog->mask & ANALOG_HATS_ALL)); Use scnprintf, this is too fragile and hard to verify. If the first snprintf overflows, the second passes a huge size_t to snprintf which will WARN. Rasmus