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 <fth...@linux-m68k.org>
> Signed-off-by: Justin Stitt <justinst...@google.com>
> ---
> 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/20240221-snprintf-checkpatch-v1-1-3ac5025b5...@google.com
> ---
> From a discussion here [1].
>
> [1]:
> https://lore.kernel.org/all/0f9c95f9-2c14-eee6-7faf-635880edc...@linux-m68k.org/
> 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" .
> $herecurr);
There really should be some sort of reference link here
similar to the one above this.
Also, I rather doubt _all_ of these should be changed just
for churn's sake.
Maybe add a test for some return value use like
if (defined($stat) &&
$stat =~ /$Lval\s*=\s*snprintf\s*\(/) {
etc...
Maybe offer to --fix it too.
