[PATCH 4.19 162/271] floppy: fix invalid pointer dereference in drive_name

From: Greg Kroah-Hartman
Date: Thu Jul 25 2019 - 11:02:14 EST

[ Upstream commit 9b04609b784027968348796a18f601aed9db3789 ]

This fixes the invalid pointer dereference in the drive_name function of
the floppy driver.

The native_format field of the struct floppy_drive_params is used as
floppy_type array index in the drive_name function. Thus, the field
should be checked the same way as the autodetect field.

To trigger the bug, one could use a value out of range and set the drive
parameters with the FDSETDRVPRM ioctl. Next, FDGETDRVTYP ioctl should
be used to call the drive_name. A floppy disk is not required to be

CAP_SYS_ADMIN is required to call FDSETDRVPRM.

The patch adds the check for a value of the native_format field to be in
the '0 <= x < ARRAY_SIZE(floppy_type)' range of the floppy_type array

The bug was found by syzkaller.

Signed-off-by: Denis Efremov <efremov@xxxxxxxxx>
Tested-by: Willy Tarreau <w@xxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
drivers/block/floppy.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
index dd49737effbf..8d69a8af8b78 100644
--- a/drivers/block/floppy.c
+++ b/drivers/block/floppy.c
@@ -3391,7 +3391,8 @@ static int fd_getgeo(struct block_device *bdev, struct hd_geometry *geo)
return 0;

-static bool valid_floppy_drive_params(const short autodetect[8])
+static bool valid_floppy_drive_params(const short autodetect[8],
+ int native_format)
size_t floppy_type_size = ARRAY_SIZE(floppy_type);
size_t i = 0;
@@ -3402,6 +3403,9 @@ static bool valid_floppy_drive_params(const short autodetect[8])
return false;

+ if (native_format < 0 || native_format >= floppy_type_size)
+ return false;
return true;

@@ -3531,7 +3535,8 @@ static int fd_locked_ioctl(struct block_device *bdev, fmode_t mode, unsigned int
SUPBOUND(size, strlen((const char *)outparam) + 1);
- if (!valid_floppy_drive_params(inparam.dp.autodetect))
+ if (!valid_floppy_drive_params(inparam.dp.autodetect,
+ inparam.dp.native_format))
return -EINVAL;
*UDP = inparam.dp;
@@ -3730,7 +3735,7 @@ static int compat_setdrvprm(int drive,
return -EPERM;
if (copy_from_user(&v, arg, sizeof(struct compat_floppy_drive_params)))
return -EFAULT;
- if (!valid_floppy_drive_params(v.autodetect))
+ if (!valid_floppy_drive_params(v.autodetect, v.native_format))
return -EINVAL;
UDP->cmos = v.cmos;