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

Lee Jones
2024-02-08T10:29:44Z

On Thu, 08 Feb 2024, Geert Uytterhoeven wrote:

> Hi Lee,
>
> Thanks for your patch!
>
> On Thu, Feb 8, 2024 at 9:48 AM Lee Jones <lee@kernel.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?

Future proofing. The idea of the effort is to rid the use entirely.

- Usage is inside a sysfs handler passing PAGE_SIZE as the size
- s/snprintf/sysfs_emit/
- Usage is inside a sysfs handler passing a bespoke value as the size
- s/snprintf/scnprintf/
- Return value used, but does *not* care about overflow
- s/snprintf/scnprintf/
- Return value used, caller *does* care about overflow
- s/snprintf/seq_buf/
- Return value not used
- s/snprintf/scnprintf/

This is the final case.

> > --- 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);

--
Lee Jones [李琼斯]