On Wed, 21 Feb 2024, Joe Perches wrote:
> On Wed, 2024-02-21 at 22:11 +0000, Justin Stitt wrote:
> > I am going to quote Lee Jones who has been doing some snprintf ->
> > scnprintf refactorings:
> >
> > "There is a general misunderstanding amongst engineers that
> > {v}snprintf() returns the length of the data *actually* encoded into the
> > destination array. However, as per the C99 standard {v}snprintf()
> > really returns the length of the data that *would have been* written if
> > there were enough space for it. This misunderstanding has led to
> > buffer-overruns in the past. It's generally considered safer to use the
> > {v}scnprintf() variants in their place (or even sprintf() in simple
> > cases). So let's do that."
> >
> > To help prevent new instances of snprintf() from popping up, let's add a
> > check to checkpatch.pl.
> >
> > Suggested-by: Finn Thain <[email protected]>
> > Signed-off-by: Justin Stitt <[email protected]>
> > ---
> > Changes in v2:
> > - Had a vim moment and deleted a character before sending the patch.
> > - Replaced the character :)
> > - Link to v1:
> > https://lore.kernel.org/r/[email protected]
> > ---
> > From a discussion here [1].
> >
> > [1]:
> > https://lore.kernel.org/all/[email protected]/
>
> > diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> []
> > @@ -7012,6 +7012,12 @@ sub process {
> > "Prefer strscpy, strscpy_pad, or __nonstring over
> > strncpy - see: https://github.com/KSPP/linux/issues/90\n"; . $herecurr);
> > }
> >
> > +# snprintf uses that should likely be {v}scnprintf
> > + if ($line =~ /\bsnprintf\s*\(\s*/) {
> > + WARN("SNPRINTF",
> > + "Prefer scnprintf over snprintf\n" .
> > $herecurr);
>
> There really should be some sort of reference link here
> similar to the one above this.
>
> Also, I rather doubt _all_ of these should be changed just
> for churn's sake.
This is for new implementations only.
Kees is planning on changing all of the current instances kernel-wide.
> Maybe add a test for some return value use like
>
> if (defined($stat) &&
> $stat =~ /$Lval\s*=\s*snprintf\s*\(/) {
> etc...
>
> Maybe offer to --fix it too.
>
--
Lee Jones [李琼斯]
