Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH 5/8] scsi: lpfc: change snprintf to scnprintf for possible
 overflow
To:     Kees Cook <keescook@chromium.org>, Willy Tarreau <w@1wt.eu>
Cc:     Silvio Cesare <silvio.cesare@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Dick Kennedy <dick.kennedy@broadcom.com>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Will Deacon <will.deacon@arm.com>, Greg KH <greg@kroah.com>
References: <20190112152844.26550-1-w@1wt.eu>
 <20190112152844.26550-5-w@1wt.eu>
 <CAGXu5jKu5br-pB3U+3PDtgcgq_nmt0C7gHLYQXV4tz3pN=S11Q@mail.gmail.com>
From:   James Smart <james.smart@broadcom.com>
Message-ID: <de134f7c-7516-cfb4-7cd2-6d96b45bdb48@broadcom.com>
Date:   Tue, 15 Jan 2019 14:41:17 -0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101
 Thunderbird/60.4.0
MIME-Version: 1.0
In-Reply-To: <CAGXu5jKu5br-pB3U+3PDtgcgq_nmt0C7gHLYQXV4tz3pN=S11Q@mail.gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
Content-Language: en-US
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


On 1/14/2019 5:15 PM, Kees Cook wrote:
> On Sat, Jan 12, 2019 at 7:29 AM Willy Tarreau<w@1wt.eu>  wrote:
>> From: Silvio Cesare<silvio.cesare@gmail.com>
>>
>> Change snprintf to scnprintf. There are generally two cases where using
>> snprintf causes problems.
>>
>> 1) Uses of size += snprintf(buf, SIZE - size, fmt, ...)
>> In this case, if snprintf would have written more characters than what the
>> buffer size (SIZE) is, then size will end up larger than SIZE. In later
>> uses of snprintf, SIZE - size will result in a negative number, leading
>> to problems. Note that size might already be too large by using
>> size = snprintf before the code reaches a case of size += snprintf.
>>
>> 2) If size is ultimately used as a length parameter for a copy back to user
>> space, then it will potentially allow for a buffer overflow and information
>> disclosure when size is greater than SIZE. When the size is used to index
>> the buffer directly, we can have memory corruption. This also means when
>> size = snprintf... is used, it may also cause problems since size may become
>> large.  Copying to userspace is mitigated by the HARDENED_USERCOPY kernel
>> configuration.
>>
>> The solution to these issues is to use scnprintf which returns the number of
>> characters actually written to the buffer, so the size variable will never
>> exceed SIZE.
>>
>> Signed-off-by: Silvio Cesare<silvio.cesare@gmail.com>
>> Cc: James Smart<james.smart@broadcom.com>
>> Cc: Dick Kennedy<dick.kennedy@broadcom.com>
>> Cc: Dan Carpenter<dan.carpenter@oracle.com>
>> Cc: Kees Cook<keescook@chromium.org>
>> Cc: Will Deacon<will.deacon@arm.com>
>> Cc: Greg KH<greg@kroah.com>
>> Signed-off-by: Willy Tarreau<w@1wt.eu>
> I think this needs Cc: stable.
>
> Reviewed-by: Kees Cook<keescook@chromium.org>
>
> -Kees
>


Reviewed-by:  James Smart <james.smart@broadcom.com>

-- james