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floppy: fix out-of-bounds read in next_valid_format

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This fixes a global out-of-bounds read access in the next_valid_format
function of the floppy driver.

The values from autodetect field of the struct floppy_drive_params are
used as indices for the floppy_type array in the next_valid_format
function 'floppy_type[DP->autodetect[probed_format]].sect'.

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

CAP_SYS_ADMIN is required to call FDSETDRVPRM.

The patch adds the check for values of the autodetect 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 21:55:21 +03:00 committed by Linus Torvalds
parent f3554aeb99
commit 5635f897ed
1 changed files with 18 additions and 0 deletions
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18
drivers/block/floppy.c
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@ -3380,6 +3380,20 @@ static int fd_getgeo(struct block_device *bdev, struct hd_geometry *geo)
return 0;
}
static bool valid_floppy_drive_params(const short autodetect[8])
{
size_t floppy_type_size = ARRAY_SIZE(floppy_type);
size_t i = 0;
for (i = 0; i < 8; ++i) {
if (autodetect[i] < 0 ||
autodetect[i] >= floppy_type_size)
return false;
}
return true;
}
static int fd_locked_ioctl(struct block_device *bdev, fmode_t mode, unsigned int cmd,
unsigned long param)
{
@ -3506,6 +3520,8 @@ 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))
return -EINVAL;
*UDP = inparam.dp;
break;
case FDGETDRVPRM:
@ -3703,6 +3719,8 @@ 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))
return -EINVAL;
mutex_lock(&floppy_mutex);
UDP->cmos = v.cmos;
UDP->max_dtr = v.max_dtr;