[PATCH 5.15 01/33] floppy: disable FDRAWCMD by default

Greg Kroah-Hartman
2022-04-29T10:46:42Z

From: Willy Tarreau <w@1wt.eu>

commit 233087ca063686964a53c829d547c7571e3f67bf upstream.

Minh Yuan reported a concurrency use-after-free issue in the floppy code
between raw_cmd_ioctl and seek_interrupt.

[ It turns out this has been around, and that others have reported the
KASAN splats over the years, but Minh Yuan had a reproducer for it and
so gets primary credit for reporting it for this fix - Linus ]

The problem is, this driver tends to break very easily and nowadays,
nobody is expected to use FDRAWCMD anyway since it was used to
manipulate non-standard formats. The risk of breaking the driver is
higher than the risk presented by this race, and accessing the device
requires privileges anyway.

Let's just add a config option to completely disable this ioctl and
leave it disabled by default. Distros shouldn't use it, and only those
running on antique hardware might need to enable it.

Link: https://lore.kernel.org/all/000000000000b71cdd05d703f6bf@google.com/
Link: https://lore.kernel.org/lkml/CAKcFiNC=MfYVW-Jt9A3=FPJpTwCD2PL_ULNCpsCVE5s8ZeBQgQ@mail.gmail.com
Link: https://lore.kernel.org/all/CAEAjamu1FRhz6StCe_55XY5s389ZP_xmCF69k987En+1z53=eg@mail.gmail.com
Reported-by: Minh Yuan <yuanmingbuaa@gmail.com>
Reported-by: syzbot+8e8958586909d62b6840@syzkaller.appspotmail.com
Reported-by: cruise k <cruise4k@gmail.com>
Reported-by: Kyungtae Kim <kt0755@gmail.com>
Suggested-by: Linus Torvalds <torvalds@linuxfoundation.org>
Tested-by: Denis Efremov <efremov@linux.com>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/block/Kconfig | 16 ++++++++++++++++
drivers/block/floppy.c | 43 ++++++++++++++++++++++++++++++++-----------
2 files changed, 48 insertions(+), 11 deletions(-)

--- a/drivers/block/Kconfig
+++ b/drivers/block/Kconfig
@@ -33,6 +33,22 @@ config BLK_DEV_FD
To compile this driver as a module, choose M here: the
module will be called floppy.

+config BLK_DEV_FD_RAWCMD
+ bool "Support for raw floppy disk commands (DEPRECATED)"
+ depends on BLK_DEV_FD
+ help
+ If you want to use actual physical floppies and expect to do
+ special low-level hardware accesses to them (access and use
+ non-standard formats, for example), then enable this.
+
+ Note that the code enabled by this option is rarely used and
+ might be unstable or insecure, and distros should not enable it.
+
+ Note: FDRAWCMD is deprecated and will be removed from the kernel
+ in the near future.
+
+ If unsure, say N.
+
config AMIGA_FLOPPY
tristate "Amiga floppy support"
depends on AMIGA
--- a/drivers/block/floppy.c
+++ b/drivers/block/floppy.c
@@ -2984,6 +2984,8 @@ static const char *drive_name(int type,
return "(null)";
}

+#ifdef CONFIG_BLK_DEV_FD_RAWCMD
+
/* raw commands */
static void raw_cmd_done(int flag)
{
@@ -3183,6 +3185,35 @@ static int raw_cmd_ioctl(int cmd, void _
return ret;
}

+static int floppy_raw_cmd_ioctl(int type, int drive, int cmd,
+ void __user *param)
+{
+ int ret;
+
+ pr_warn_once("Note: FDRAWCMD is deprecated and will be removed from the kernel in the near future.\n");
+
+ if (type)
+ return -EINVAL;
+ if (lock_fdc(drive))
+ return -EINTR;
+ set_floppy(drive);
+ ret = raw_cmd_ioctl(cmd, param);
+ if (ret == -EINTR)
+ return -EINTR;
+ process_fd_request();
+ return ret;
+}
+
+#else /* CONFIG_BLK_DEV_FD_RAWCMD */
+
+static int floppy_raw_cmd_ioctl(int type, int drive, int cmd,
+ void __user *param)
+{
+ return -EOPNOTSUPP;
+}
+
+#endif
+
static int invalidate_drive(struct block_device *bdev)
{
/* invalidate the buffer track to force a reread */
@@ -3371,7 +3402,6 @@ static int fd_locked_ioctl(struct block_
{
int drive = (long)bdev->bd_disk->private_data;
int type = ITYPE(drive_state[drive].fd_device);
- int i;
int ret;
int size;
union inparam {
@@ -3522,16 +3552,7 @@ static int fd_locked_ioctl(struct block_
outparam = &write_errors[drive];
break;
case FDRAWCMD:
- if (type)
- return -EINVAL;
- if (lock_fdc(drive))
- return -EINTR;
- set_floppy(drive);
- i = raw_cmd_ioctl(cmd, (void __user *)param);
- if (i == -EINTR)
- return -EINTR;
- process_fd_request();
- return i;
+ return floppy_raw_cmd_ioctl(type, drive, cmd, (void __user *)param);
case FDTWADDLE:
if (lock_fdc(drive))
return -EINTR;