linux-hardening - Re: [PATCH 03/10] scsi: NCR5380: Replace snprintf() with the safer scnprintf() variant

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Message-ID: <CAMuHMdX72mpGgb3Wp0WRX3V78nn+bWUqiYz25CjeMNPpWaPmxg@mail.gmail.com>
Date: Thu, 8 Feb 2024 11:22:30 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Lee Jones <lee@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org, 
	Finn Thain <fthain@...ux-m68k.org>, Michael Schmitz <schmitzmic@...il.com>, 
	"James E.J. Bottomley" <jejb@...ux.ibm.com>, "Martin K. Petersen" <martin.petersen@...cle.com>, drew@...orado.edu, 
	Tnx to <Thomas_Roesch@...maus.de>, linux-scsi@...r.kernel.org
Subject: Re: [PATCH 03/10] scsi: NCR5380: Replace snprintf() with the safer
 scnprintf() variant

Hi Lee,

Thanks for your patch!

On Thu, Feb 8, 2024 at 9:48 AM Lee Jones <lee@...nel.org> wrote:
> 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.

Confused... The return value is not used at all?

> --- a/drivers/scsi/NCR5380.c
> +++ b/drivers/scsi/NCR5380.c
> @@ -421,14 +421,14 @@ static int NCR5380_init(struct Scsi_Host *instance, int flags)
>         if (!hostdata->work_q)
>                 return -ENOMEM;
>
> -       snprintf(hostdata->info, sizeof(hostdata->info),
> -               "%s, irq %d, io_port 0x%lx, base 0x%lx, can_queue %d, cmd_per_lun %d, sg_tablesize %d, this_id %d, flags { %s%s%s}",
> -               instance->hostt->name, instance->irq, hostdata->io_port,
> -               hostdata->base, instance->can_queue, instance->cmd_per_lun,
> -               instance->sg_tablesize, instance->this_id,
> -               hostdata->flags & FLAG_DMA_FIXUP     ? "DMA_FIXUP "     : "",
> -               hostdata->flags & FLAG_NO_PSEUDO_DMA ? "NO_PSEUDO_DMA " : "",
> -               hostdata->flags & FLAG_TOSHIBA_DELAY ? "TOSHIBA_DELAY " : "");
> +       scnprintf(hostdata->info, sizeof(hostdata->info),
> +                "%s, irq %d, io_port 0x%lx, base 0x%lx, can_queue %d, cmd_per_lun %d, sg_tablesize %d, this_id %d, flags { %s%s%s}",
> +                instance->hostt->name, instance->irq, hostdata->io_port,
> +                hostdata->base, instance->can_queue, instance->cmd_per_lun,
> +                instance->sg_tablesize, instance->this_id,
> +                hostdata->flags & FLAG_DMA_FIXUP     ? "DMA_FIXUP "     : "",
> +                hostdata->flags & FLAG_NO_PSEUDO_DMA ? "NO_PSEUDO_DMA " : "",
> +                hostdata->flags & FLAG_TOSHIBA_DELAY ? "TOSHIBA_DELAY " : "");
>
>         NCR5380_write(INITIATOR_COMMAND_REG, ICR_BASE);
>         NCR5380_write(MODE_REG, MR_BASE);

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds