linux-kernel - Re: [PATCH 5/8] scsi: lpfc: change snprintf to scnprintf for possible overflow

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Message-ID: <d23fb974-2486-a138-4aae-3575f730c4fd@broadcom.com>
Date:   Wed, 20 Mar 2019 13:27:02 -0700
From:   James Smart <james.smart@...adcom.com>
To:     Greg KH <greg@...ah.com>
Cc:     Kees Cook <keescook@...omium.org>, Willy Tarreau <w@....eu>,
        Silvio Cesare <silvio.cesare@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Dick Kennedy <dick.kennedy@...adcom.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCH 5/8] scsi: lpfc: change snprintf to scnprintf for possible
 overflow

On 3/20/2019 10:39 AM, Greg KH wrote:
> On Tue, Jan 15, 2019 at 02:41:17PM -0800, James Smart wrote:
>> On 1/14/2019 5:15 PM, Kees Cook wrote:
>>> On Sat, Jan 12, 2019 at 7:29 AM Willy Tarreau<w@....eu>  wrote:
>>>> From: Silvio Cesare<silvio.cesare@...il.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@...il.com>
>>>> Cc: James Smart<james.smart@...adcom.com>
>>>> Cc: Dick Kennedy<dick.kennedy@...adcom.com>
>>>> Cc: Dan Carpenter<dan.carpenter@...cle.com>
>>>> Cc: Kees Cook<keescook@...omium.org>
>>>> Cc: Will Deacon<will.deacon@....com>
>>>> Cc: Greg KH<greg@...ah.com>
>>>> Signed-off-by: Willy Tarreau<w@....eu>
>>> I think this needs Cc: stable.
>>>
>>> Reviewed-by: Kees Cook<keescook@...omium.org>
>>>
>>> -Kees
>>>
>>
>> Reviewed-by:  James Smart <james.smart@...adcom.com>
> What ever happened to this patch?  Did it get dropped somehow?
>
> thanks,
>
> greg k-h

I assume it wasn't pulled in by the scsi maintainers. I'll go ping them.

-- james