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firewire: cdev: fix information leak

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A userspace client got to see uninitialized stack-allocated memory if it
specified an _IOC_READ type of ioctl and an argument size larger than
expected by firewire-core's ioctl handlers (but not larger than the
core's union ioctl_arg).

Fix this by clearing the requested buffer size to zero, but only at _IOR
ioctls.  This way, there is almost no runtime penalty to legitimate
ioctls.  The only legitimate _IOR is FW_CDEV_IOC_GET_CYCLE_TIMER with 12
or 16 bytes to memset.

[Another way to fix this would be strict checking of argument size (and
possibly direction) vs. command number.  However, we then need a lookup
table, and we need to allow for slight size deviations in case of 32bit
userland on 64bit kernel.]

Reported-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
This commit is contained in:
Stefan Richter 2010-04-07 08:30:50 +02:00
parent 385ab5bcd4
commit 9cac00b8f0
1 changed files with 9 additions and 9 deletions
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18
drivers/firewire/core-cdev.c
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@ -1356,24 +1356,24 @@ static int dispatch_ioctl(struct client *client,
return -ENODEV;
if (_IOC_TYPE(cmd) != '#' ||
_IOC_NR(cmd) >= ARRAY_SIZE(ioctl_handlers))
_IOC_NR(cmd) >= ARRAY_SIZE(ioctl_handlers) ||
_IOC_SIZE(cmd) > sizeof(buffer))
return -EINVAL;
if (_IOC_DIR(cmd) & _IOC_WRITE) {
if (_IOC_SIZE(cmd) > sizeof(buffer) ||
copy_from_user(&buffer, arg, _IOC_SIZE(cmd)))
if (_IOC_DIR(cmd) == _IOC_READ)
memset(&buffer, 0, _IOC_SIZE(cmd));
if (_IOC_DIR(cmd) & _IOC_WRITE)
if (copy_from_user(&buffer, arg, _IOC_SIZE(cmd)))
return -EFAULT;
}
ret = ioctl_handlers[_IOC_NR(cmd)](client, &buffer);
if (ret < 0)
return ret;
if (_IOC_DIR(cmd) & _IOC_READ) {
if (_IOC_SIZE(cmd) > sizeof(buffer) ||
copy_to_user(arg, &buffer, _IOC_SIZE(cmd)))
if (_IOC_DIR(cmd) & _IOC_READ)
if (copy_to_user(arg, &buffer, _IOC_SIZE(cmd)))
return -EFAULT;
}
return ret;
}