From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753828AbeDSRBz (ORCPT ); Thu, 19 Apr 2018 13:01:55 -0400 Received: from mail-wr0-f193.google.com ([209.85.128.193]:43929 "EHLO mail-wr0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753649AbeDSRBv (ORCPT ); Thu, 19 Apr 2018 13:01:51 -0400 X-Google-Smtp-Source: AIpwx4+BPXigypatvbOHP7aHMdnF2dLIc+DTsA35qYgsEg0q7U+KwC+fI2kS0Gjjsi+i+fGSahz7KQ== Reply-To: alex.popov@linux.com Subject: Re: [v2 1/1] i2c: dev: prevent ZERO_SIZE_PTR deref in i2cdev_ioctl_rdwr() To: =?UTF-8?Q?Uwe_Kleine-K=c3=b6nig?= Cc: Wolfram Sang , linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org, sil2review@lists.osadl.org, Dmitry Vyukov , syzkaller@googlegroups.com References: <1524140962-25639-1-git-send-email-alex.popov@linux.com> <20180419134902.6l5jsf4wpqfiaskj@pengutronix.de> From: Alexander Popov Openpgp: preference=signencrypt Autocrypt: addr=alex.popov@linux.com; 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Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20180419134902.6l5jsf4wpqfiaskj@pengutronix.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19.04.2018 16:49, Uwe Kleine-König wrote: > On Thu, Apr 19, 2018 at 03:29:22PM +0300, Alexander Popov wrote: >> i2cdev_ioctl_rdwr() allocates i2c_msg.buf using memdup_user(), which >> returns ZERO_SIZE_PTR if i2c_msg.len is zero. >> >> Currently i2cdev_ioctl_rdwr() always dereferences the buf pointer in case >> of I2C_M_RD | I2C_M_RECV_LEN transfer. That causes a kernel oops in >> case of zero len. >> >> Let's check the len against zero before dereferencing buf pointer. >> >> This issue was triggered by syzkaller. >> >> Signed-off-by: Alexander Popov >> --- >> drivers/i2c/i2c-dev.c | 1 + >> 1 file changed, 1 insertion(+) >> >> diff --git a/drivers/i2c/i2c-dev.c b/drivers/i2c/i2c-dev.c >> index 036a03f..5790bc8 100644 >> --- a/drivers/i2c/i2c-dev.c >> +++ b/drivers/i2c/i2c-dev.c >> @@ -280,6 +280,7 @@ static noinline int i2cdev_ioctl_rdwr(struct i2c_client *client, >> */ >> if (msgs[i].flags & I2C_M_RECV_LEN) { >> if (!(msgs[i].flags & I2C_M_RD) || >> + !msgs[i].len || > > I'd prefer > > msgs[i].len > 0 Excuse me, it will be wrong. We stop if len is 0 to avoid the following ZERO_SIZE_PTR dereference. > here instead of > > !msgs[i].len I can change it to "msgs[i].len == 0". But is it really important? I've carefully tested the current version with the original repro. It works correct. > because I can parse that more easily. Semantically the patch is fine and > can have my > > Reviewed-by: Uwe Kleine-König > >> msgs[i].buf[0] < 1 || >> msgs[i].len < msgs[i].buf[0] + >> I2C_SMBUS_BLOCK_MAX) { Best regards, Alexander