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floppy: fix invalid pointer dereference in drive_name 

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>
This commit is contained in:
Denis Efremov 2019-07-12 21:55:22 +03:00 committed by Linus Torvalds
parent 5635f897ed
commit 9b04609b78
1 changed files with 8 additions and 3 deletions
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11
drivers/block/floppy.c
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@ -3380,7 +3380,8 @@ 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;
@ -3391,6 +3392,9 @@ 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;
}
@ -3520,7 +3524,8 @@ static int fd_locked_ioctl(struct block_device *bdev, fmode_t mode, unsigned int
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;
@ -3719,7 +3724,7 @@ 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;