linux-kernel - Re: [PATCH v2] tile: avoid errors from truncating long strings in mpipe gxio

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Date:	Mon, 11 Aug 2014 22:43:36 +0200
From:	Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>
To:	Randy Dunlap <rdunlap@...radead.org>
Cc:	Chris Metcalf <cmetcalf@...era.com>,
	"David S. Miller" <davem@...emloft.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] tile: avoid errors from truncating long strings in
 mpipe gxio

2014-08-07 8:43 GMT+02:00 Randy Dunlap <rdunlap@...radead.org>:
> On 08/06/14 11:16, Chris Metcalf wrote:
>> Using strncpy() will just silently truncate long strings; we should
>> instead return an appropriate error.  Using strlcpy() would suffer from
>> the same problem.  Instead, use strnlen()+memcpy(), and add an
>> error-checking step to make sure the lengths are reasonable.
>>
>> I called the convenience wrapper strscpy(), and a case could be made for
>> making it more generic (possibly with a better name), but that seems
>> outside the scope of this initial commit.
>
> Well, having looked at the function before I read this comment, my first
> thought was that it should be added to lib/string.c for general
> availability.
>
>>
>> Signed-off-by: Chris Metcalf <cmetcalf@...era.com>
>> ---
>> v2: use strnlen instead of strlen
>>
>>  arch/tile/gxio/mpipe.c | 30 +++++++++++++++++++++++++-----
>>  1 file changed, 25 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/tile/gxio/mpipe.c b/arch/tile/gxio/mpipe.c
>> index 5301a9ffbae1..27a56be8d583 100644
>> --- a/arch/tile/gxio/mpipe.c
>> +++ b/arch/tile/gxio/mpipe.c
>> @@ -29,6 +29,25 @@
>>  /* HACK: Avoid pointless "shadow" warnings. */
>>  #define link link_shadow
>>
>> +/*
>> + * Use this routine to avoid copying too-long strings.  Unlike strncpy
>> + * or strlcpy, we don't enable programmers who don't check return codes;
>> + * partially-copied strings can be problematic.  The routine returns
>> + * the total number of bytes copied (including the trailing NUL) or
>> + * zero if the buffer wasn't big enough.
>> + */
>> +static size_t strscpy(char *dest, const char *src, size_t size)
>> +{
>> +     size_t ret = strnlen(src, size) + 1;
>> +     if (ret > size) {
>> +             if (size)
>> +                     dest[0] = '\0';
>> +             return 0;
>> +     }
>> +     memcpy(dest, src, ret);
>> +     return ret;
>> +}
>
> --
> ~Randy


Hi

Sounds like a great idea!

Do it Chris!  Randy?


Kind regards
Rickard Strandqvist
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