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Date:   Tue, 15 Jan 2019 14:41:17 -0800
From:   James Smart <>
To:     Kees Cook <>, Willy Tarreau <>
Cc:     Silvio Cesare <>,
        LKML <>,
        Dick Kennedy <>,
        Dan Carpenter <>,
        Will Deacon <>, Greg KH <>
Subject: Re: [PATCH 5/8] scsi: lpfc: change snprintf to scnprintf for possible

On 1/14/2019 5:15 PM, Kees Cook wrote:
> On Sat, Jan 12, 2019 at 7:29 AM Willy Tarreau<>  wrote:
>> From: Silvio Cesare<>
>> 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<>
>> Cc: James Smart<>
>> Cc: Dick Kennedy<>
>> Cc: Dan Carpenter<>
>> Cc: Kees Cook<>
>> Cc: Will Deacon<>
>> Cc: Greg KH<>
>> Signed-off-by: Willy Tarreau<>
> I think this needs Cc: stable.
> Reviewed-by: Kees Cook<>
> -Kees

Reviewed-by:  James Smart <>

-- james

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