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Sat, 15 Sep 2018 01:32:30 +0000 Received: from CY4PR21MB0776.namprd21.prod.outlook.com ([fe80::151:b6fe:32c8:cccd]) by CY4PR21MB0776.namprd21.prod.outlook.com ([fe80::151:b6fe:32c8:cccd%9]) with mapi id 15.20.1164.008; Sat, 15 Sep 2018 01:32:30 +0000 From: Sasha Levin To: "stable@vger.kernel.org" , "linux-kernel@vger.kernel.org" CC: Jann Horn , Boris Brezillon , Sasha Levin Subject: [PATCH AUTOSEL 4.14 05/57] mtdchar: fix overflows in adjustment of `count` Thread-Topic: [PATCH AUTOSEL 4.14 05/57] mtdchar: fix overflows in adjustment of `count` Thread-Index: AQHUTJP4m3JxavioKUK8IFt0JFZ1Pg== Date: Sat, 15 Sep 2018 01:32:30 +0000 Message-ID: <20180915013223.179909-5-alexander.levin@microsoft.com> References: <20180915013223.179909-1-alexander.levin@microsoft.com> In-Reply-To: <20180915013223.179909-1-alexander.levin@microsoft.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [52.168.54.252] x-ms-publictraffictype: Email x-microsoft-exchange-diagnostics: 1;CY4PR21MB0117;6:J3am4i8PVR3/1306ogs2e99wI0bQDZarfX4edUEN53jp81MSJnuwYfo3dJSJYkQKBajiuJdmntCXMj/boVZ6/jn/rVrpsiXPfFwAH8m1z0aIQXq0w4kR8GhhlVbKAU6TAr8nLROuiWxJJJ189KLciEVonlM7voQoUN9Y9FzDMCopwxp/MOw7Xr/bAFObZOFd1jxzhbAWgMkCaHbUUEIjZldS/s3pf7kBVCfm1X6qauzU1PWlIQkevpDX9PKRPNCaVM/4TyQwXPi9BuY2ZG6wOt3EsxOpKHEj3XxZ/6QXNu3o/V5D5VUOY97VkLTQUFvN+U23r52qEVa3idKOwF47R0C6ZBCe+M9BORz6kWxL88SyitNR24uWBe19SPKKocn2+Xqq7mFB1o5TRoBppKbkQOZxgq8OclJzHncR5Yhm23bVwi3H7Anrt+jRy/rV+r3ZtZxMeSr47jpwTcx0sTv5fQ==;5:YslcQTxqXn+4LP6Yn9DQeLlXducDeLyvYSoBlvsYMjs+hJg4wY1oYdW5gQNMRJyEZFPEFRM1QViq/VCXvkmcJeXONQrJJlQaC489yopS/BgZuBf0XuEd6xtlxK9aHFeMPw6sFJ3JWgLVlEygbZp3Ie3d63hMgxzMzz+YcMnxGYA=;7:dG4h3CtOk9cJ8f630tb8E1dD8dWjxYUj+OfCI0R8ZsVlpZY585Ols3rW4DJwO8szpfJJh4JNy5QN2n7OyK9bPdkqupLyq/dt3FKH1DRoJ0z4DxgRjPXr28EYVNmlX2RZMhQ6I+PcXd0i5c7sN6eMvtIKqMZTNCk2+nN5x7lXT7Tmkt5BkQdIS+gNO+JiFiCoB38nv9xURbagSkNhPSZTGDJGd7B9E0VGm2lu3eCmvi1S7MKEiOjof8yKBR3PuLh4 x-ms-office365-filtering-correlation-id: 9f1f4c4f-d79e-4388-2bbb-08d61aab1a96 x-ms-office365-filtering-ht: Tenant x-microsoft-antispam: BCL:0;PCL:0;RULEID:(7020095)(4652040)(8989137)(4534165)(4627221)(201703031133081)(201702281549075)(8990107)(5600074)(711020)(4618075)(2017052603328)(7193020);SRVR:CY4PR21MB0117; 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received-spf: None (protection.outlook.com: microsoft.com does not designate permitted sender hosts) x-microsoft-antispam-message-info: aR1qqn5v3OrSCJEwJdFs/KJAujR+yQT2pz47qugtUxZauWGuY+Oacm0erpSDld240l53IBpL6lGFTOYGALRBlXvE1OGu8fmEUCuPp34MuvBgb5vwgDYuWdEClyDz6yqCmQ2GRqxtM9Vkhec1OlJlatpIs/0zh5RJtQXTwr5CjfoCz+n2Iw8KMizOETqArN/eEVuvO+bizwdRFmYWZtoUp/wmU1waOvVJu/sXYjIRFIjqUkyDHeA/8rNAYFy92vTXm0eJrMn7tbIzPYXNoadBCbmij12qZ7J82VVi5wcH052ZIxkhZ/eGf59RNGe723Bf71/0O3WAwbCAGy0EaVf/JqNRfPJyHL0vXLieC/hs83A= spamdiagnosticoutput: 1:99 spamdiagnosticmetadata: NSPM Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: microsoft.com X-MS-Exchange-CrossTenant-Network-Message-Id: 9f1f4c4f-d79e-4388-2bbb-08d61aab1a96 X-MS-Exchange-CrossTenant-originalarrivaltime: 15 Sep 2018 01:32:30.6345 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47 X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY4PR21MB0117 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Jann Horn [ Upstream commit 6c6bc9ea84d0008024606bf5ba10519e20d851bf ] The first checks in mtdchar_read() and mtdchar_write() attempt to limit `count` such that `*ppos + count <=3D mtd->size`. However, they ignore the possibility of `*ppos > mtd->size`, allowing the calculation of `count` to wrap around. `mtdchar_lseek()` prevents seeking beyond mtd->size, but the pread/pwrite syscalls bypass this. I haven't found any codepath on which this actually causes dangerous behavior, but it seems like a sensible change anyway. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Jann Horn Signed-off-by: Boris Brezillon Signed-off-by: Sasha Levin --- drivers/mtd/mtdchar.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c index b25f444c5914..fa4d12217652 100644 --- a/drivers/mtd/mtdchar.c +++ b/drivers/mtd/mtdchar.c @@ -160,8 +160,12 @@ static ssize_t mtdchar_read(struct file *file, char __= user *buf, size_t count, =20 pr_debug("MTD_read\n"); =20 - if (*ppos + count > mtd->size) - count =3D mtd->size - *ppos; + if (*ppos + count > mtd->size) { + if (*ppos < mtd->size) + count =3D mtd->size - *ppos; + else + count =3D 0; + } =20 if (!count) return 0; @@ -246,7 +250,7 @@ static ssize_t mtdchar_write(struct file *file, const c= har __user *buf, size_t c =20 pr_debug("MTD_write\n"); =20 - if (*ppos =3D=3D mtd->size) + if (*ppos >=3D mtd->size) return -ENOSPC; =20 if (*ppos + count > mtd->size) --=20 2.17.1