Re: [PATCH 05/10] scsi: aacraid: linit: Replace snprintf() with the safer scnprintf() variant

Kees Cook
2024-02-10T07:03:28Z

On Thu, Feb 08, 2024 at 08:44:17AM +0000, Lee Jones 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.
>
> Link: https://lwn.net/Articles/69419/
> Link: https://github.com/KSPP/linux/issues/105
> Signed-off-by: Lee Jones <lee@kernel.org>
> ---
> Cc: Adaptec OEM Raid Solutions <aacraid@microsemi.com>
> Cc: "James E.J. Bottomley" <jejb@linux.ibm.com>
> Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
> Cc: "PMC-Sierra, Inc" <aacraid@pmc-sierra.com>
> Cc: linux-scsi@vger.kernel.org
> ---
> drivers/scsi/aacraid/linit.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/scsi/aacraid/linit.c b/drivers/scsi/aacraid/linit.c
> index 69526e2bd2e78..0e47d9c4cff23 100644
> --- a/drivers/scsi/aacraid/linit.c
> +++ b/drivers/scsi/aacraid/linit.c
> @@ -583,7 +583,7 @@ static ssize_t aac_show_unique_id(struct device *dev,
> if (sdev_channel(sdev) == CONTAINER_CHANNEL)
> memcpy(sn, aac->fsa_dev[sdev_id(sdev)].identifier, sizeof(sn));
>
> - return snprintf(buf, 16 * 2 + 2,
> + return scnprintf(buf, 16 * 2 + 2,
> "%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X\n",
> sn[0], sn[1], sn[2], sn[3],
> sn[4], sn[5], sn[6], sn[7],

I'm confused about this conversion and the original size argument. Isn't
this also a sysfs entry? Size should be PAGE_SIZE, or it should be
replaced with sysfs_emit().

-Kees

> @@ -1302,13 +1302,13 @@ static ssize_t aac_show_serial_number(struct device *device,
> int len = 0;
>
> if (le32_to_cpu(dev->adapter_info.serial[0]) != 0xBAD0)
> - len = snprintf(buf, 16, "%06X\n",
> + len = scnprintf(buf, 16, "%06X\n",
> le32_to_cpu(dev->adapter_info.serial[0]));
> if (len &&
> !memcmp(&dev->supplement_adapter_info.mfg_pcba_serial_no[
> sizeof(dev->supplement_adapter_info.mfg_pcba_serial_no)-len],
> buf, len-1))
> - len = snprintf(buf, 16, "%.*s\n",
> + len = scnprintf(buf, 16, "%.*s\n",
> (int)sizeof(dev->supplement_adapter_info.mfg_pcba_serial_no),
> dev->supplement_adapter_info.mfg_pcba_serial_no);
>
> --
> 2.43.0.594.gd9cf4e227d-goog
>
>

--
Kees Cook