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

[Jürgen Groß <jgross@xxxxxxxx>]

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.


Juergen