Re: [PATCH v5] checkpatch: add check for snprintf to scnprintf

[Christophe JAILLET]

Le 22/04/2024 à 23:33, Justin Stitt a écrit :
> 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 <fthain@xxxxxxxxxxxxxx>
> Signed-off-by: Justin Stitt <justinstitt@xxxxxxxxxx>
> ---
> Changes in v5:
> - use capture groups to let the user know which variation they used
> - Link to v4: https://lore.kernel.org/r/20240408-snprintf-checkpatch-v4-1-8697c96ac94b@xxxxxxxxxx
>
> Changes in v4:
> - also check for vsnprintf variant (thanks Bill)
> - Link to v3: https://lore.kernel.org/r/20240315-snprintf-checkpatch-v3-1-a451e7664306@xxxxxxxxxx
>
> Changes in v3:
> - fix indentation
> - add reference link (https://github.com/KSPP/linux/issues/105) (thanks Joe)
> - Link to v2: https://lore.kernel.org/r/20240221-snprintf-checkpatch-v2-1-9baeb59dae30@xxxxxxxxxx
>
> 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-v1-1-3ac5025b5961@xxxxxxxxxx
> ---
>  From a discussion here [1].
>
> [1]: https://lore.kernel.org/all/0f9c95f9-2c14-eee6-7faf-635880edcea4@xxxxxxxxxxxxxx/
> ---
>   scripts/checkpatch.pl | 6 ++++++
>   1 file changed, 6 insertions(+)
>
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index 9c4c4a61bc83..b7404e53c554 100755
> --- 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"; . $herecurr);
>   		}
>   
> +# {v}snprintf uses that should likely be {v}scnprintf
> +		if ($line =~ /\b((v|)snprintf\s*\()/) {

Nit: I think that /\b((v|)snprintf)\s*\(/) would be nice.
Otherwise, <spaces>( would be added to the message.

CJ

> +			WARN("SNPRINTF",
> +			     "Prefer ${2}scnprintf over $1 - see: https://github.com/KSPP/linux/issues/105\n"; . $herecurr);
> +		}
> +
>   # ethtool_sprintf uses that should likely be ethtool_puts
>   		if ($line =~ /\bethtool_sprintf\s*\(\s*$FuncArg\s*,\s*$FuncArg\s*\)/) {
>   			if (WARN("PREFER_ETHTOOL_PUTS",
>
> ---
> base-commit: b401b621758e46812da61fa58a67c3fd8d91de0d
> change-id: 20240221-snprintf-checkpatch-a864ed67ebd0
>
> Best regards,
> --
> Justin Stitt <justinstitt@xxxxxxxxxx>