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SubjectRe: [PATCH v3] floppy: hide invalid floppy disk types
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Hi,

On 12/9/19 12:32 PM, Moritz Müller wrote:
> In some cases floppy disks are being indexed, even though no actual
> device exists. In our case this was caused by the CMOS-RAM having a few
> peculiar bits. This caused a non-existent floppy disk of the type 13 (in
> our case) to be registered as an possibly mountable device, even though
> it could not be mounted by any user.
>
> We believe this to be an instance of this bug:
>
> https://bugzilla.kernel.org/show_bug.cgi?id=13486
> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/384579
>
> This patch adds the option FLOPPY_ALLOW_UNKNOWN_TYPES to prevent the
> additional check that fixed the issue on our reference system, and
> increases the startup time of affected systems by over a minute.
>
> Co-developed-by: Philip K. <philip@warpmail.net>
> Signed-off-by: Philip K. <philip@warpmail.net>
> Signed-off-by: Moritz Müller <moritzm.mueller@posteo.de>

Thank you for the patch!

Have you tested your patch with FLOPPY_ALLOW_UNKNOWN_TYPES and without
FLOPPY_ALLOW_UNKNOWN_TYPES?

I will answer about motivation for this change in V2 branch of the patch.

> ---
> drivers/block/Kconfig | 10 ++++++++++
> drivers/block/floppy.c | 6 ++++++
> 2 files changed, 16 insertions(+)
>
> diff --git a/drivers/block/Kconfig b/drivers/block/Kconfig
> index 1bb8ec575352..9e6b32c50b67 100644
> --- a/drivers/block/Kconfig
> +++ b/drivers/block/Kconfig
> @@ -72,6 +72,16 @@ config AMIGA_Z2RAM
> To compile this driver as a module, choose M here: the
> module will be called z2ram.
>
> +config FLOPPY_ALLOW_UNKNOWN_TYPES
> + bool "Allow floppy disks of unknown type to be registered."
> + default n
> + help
> + Select this option if you want the Kernel to register floppy
> + disks of an unknown type.
> +
> + This should usually not be enabled, because of cases where the
> + system falsely recognizes a non-existent floppy disk as mountable.
> +
> config CDROM
> tristate
> select BLK_SCSI_REQUEST
> diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
> index 485865fd0412..9439444d46d0 100644
> --- a/drivers/block/floppy.c
> +++ b/drivers/block/floppy.c
> @@ -3949,7 +3949,11 @@ static void __init config_types(void)
> } else
> allowed_drive_mask &= ~(1 << drive);
> } else {
> +#ifdef CONFIG_FLOPPY_ALLOW_UNKNOWN_TYPES
> params = &default_drive_params[0].params;
> +#else
> + params = UDP;
> +#endif
> snprintf(temparea, sizeof(temparea),
> "unknown type %d (usb?)", type);
> name = temparea;

Maybe just skip the else branch completely here? This will omit
snprintf, following if (name) block and UDP update.

+#ifdef CONFIG_FLOPPY_ALLOW_UNKNOWN_TYPES
params = &default_drive_params[0].params;
snprintf(temparea, sizeof(temparea),
"unknown type %d (usb?)", type);
name = temparea;
+#else
+ continue;
+#endif


> @@ -4518,7 +4520,10 @@ static bool floppy_available(int drive)
> return false;
> if (fdc_state[FDC(drive)].version == FDC_NONE)
> return false;
> +#ifndef CONFIG_FLOPPY_ALLOW_UNKNOWN_TYPES
> + if (UDP->cmos >= ARRAY_SIZE(default_drive_params))
> + return false;
> +#endif
> return true;
> }
>
>

Thanks,
Denis

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