Re: [PATCH 1/2] tools: use memcpy instead of strncpy in getBridge

[Bertrand Marquis <Bertrand.Marquis@xxxxxxx>]

Hi Jurgen,

> On 6 Oct 2020, at 09:19, Jürgen Groß <jgross@xxxxxxxx> wrote:
> 
> On 06.10.20 09:51, Bertrand Marquis wrote:
>>> On 6 Oct 2020, at 05:34, Jürgen Groß <jgross@xxxxxxxx> wrote:
>>> 
>>> On 05.10.20 18:02, Bertrand Marquis wrote:
>>>> Use memcpy in getBridge to prevent gcc warnings about truncated
>>>> strings. We know that we might truncate it, so the gcc warning
>>>> here is wrong.
>>>> Revert previous change changing buffer sizes as bigger buffers
>>>> are not needed.
>>>> Signed-off-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
>>>> ---
>>>>  tools/libs/stat/xenstat_linux.c | 9 +++++++--
>>>>  1 file changed, 7 insertions(+), 2 deletions(-)
>>>> diff --git a/tools/libs/stat/xenstat_linux.c 
>>>> b/tools/libs/stat/xenstat_linux.c
>>>> index d2ee6fda64..1db35c604c 100644
>>>> --- a/tools/libs/stat/xenstat_linux.c
>>>> +++ b/tools/libs/stat/xenstat_linux.c
>>>> @@ -78,7 +78,12 @@ static void getBridge(char *excludeName, char *result, 
>>>> size_t resultLen)
>>>>                            sprintf(tmp, "/sys/class/net/%s/bridge", 
>>>> de->d_name);
>>>>                                    if (access(tmp, F_OK) == 0) {
>>>> -                                  strncpy(result, de->d_name, resultLen);
>>>> +                                  /*
>>>> +                                   * Do not use strncpy to prevent 
>>>> compiler warning with
>>>> +                                   * gcc >= 10.0
>>>> +                                   * If de->d_name is longer then 
>>>> resultLen we truncate it
>>>> +                                   */
>>>> +                                  memcpy(result, de->d_name, resultLen - 
>>>> 1);
>>> 
>>> I think you want min(NAME_MAX, resultLen - 1) for the length.
>> true, I will fix that and send a v2.
> 
> Hmm, maybe you should use
> 
> min(strnlen(de->d_name, NAME_MAX), resultLen - 1)
> 
> for the case that de->d_name is near the end of a page, as otherwise
> you could try to copy unallocated space.
> 

Agree, I will do that.

Cheers
Bertrand