[PATCH 4.9 106/223] floppy: fix invalid pointer dereference in drive_name

Greg Kroah-Hartman
2019-08-02T09:50:54Z

[ 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
inserted.

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
indices.

The bug was found by syzkaller.

Signed-off-by: Denis Efremov <efremov@ispras.ru>
Tested-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/block/floppy.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)

--- a/drivers/block/floppy.c
+++ b/drivers/block/floppy.c
@@ -3384,7 +3384,8 @@ static int fd_getgeo(struct block_device
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;
@@ -3395,6 +3396,9 @@ static bool valid_floppy_drive_params(co
return false;
}

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

@@ -3524,7 +3528,8 @@ static int fd_locked_ioctl(struct block_
SUPBOUND(size, strlen((const char *)outparam) + 1);
break;
case FDSETDRVPRM:
- 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;
break;
@@ -3723,7 +3728,7 @@ 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;
mutex_lock(&floppy_mutex);
UDP->cmos = v.cmos;