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Date: Fri, 20 Dec 2013 12:12:55 +0300
From: Dan Carpenter <dan.carpenter@oracle.com>
To: Wenliang Fan <fanwlexca@gmail.com>
Cc: gregkh <gregkh@linuxfoundation.org>, klmckinney1 <klmckinney1@gmail.com>,
        tulinizer <tulinizer@gmail.com>, devel <devel@driverdev.osuosl.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] drivers/staging/bcm: Integer overflow
Message-ID: <20131220091255.GR5443@mwanda>
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On Fri, Dec 20, 2013 at 04:51:45PM +0800, Wenliang Fan wrote:
> Thanks for your advice.
> But the variable 'psFlash2xReadWrite->offset' in '
> *drivers/staging/bcm/nvm.c*:validateFlash2xReadWrite()' is also comes from
> user space, which would cause an integer overflow in the following line:
> 
> if ((uiSectStartOffset + psFlash2xReadWrite->offset + uiNumOfBytes) <=
> uiSectEndOffset)
> 
> in '*drivers/staging/bcm/**nvm.c*: validateFlash2xReadWrite()',
> and another integer overflow in the following line:
> 
> 
> ReadOffset = ReadOffset + ReadBytes; (or WriteOffset = WriteOffset +
> WriteBytes;)
> 
> in '*drivers/staging/bcm/**Bcmchar.c*: bcm_char_ioctl()'.
> 

Alright, fine.  But the new check is messy.  Do it like this:

	/* these are user controlled and can lead to integer overflows */
	if (psFlash2xReadWrite->offset > uiSectEndOffset)
		return false;
	if (uiNumOfBytes > uiSectEndOffset)
		return false;
	if (uiSectStartOffset + psFlash2xReadWrite->offset + uiNumOfBytes > uiSectEndOffset)
		return false;

	return true;

That way each step is simpler to understand.  People are too fond of
compound conditions... *grumble*.

regards,
dan carpenter