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 legit ioctls.
The only legit _IOR is FW_CDEV_IOC_GET_CYCLE_TIMER with 12...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>
---
drivers/firewire/core-cdev.c | 18 ++++++++++--------
1 file changed, 10 insertions(+), 8 deletions(-)
Index: b/drivers/firewire/core-cdev.c
===================================================================
--- a/drivers/firewire/core-cdev.c
+++ b/drivers/firewire/core-cdev.c
@@ -1346,41 +1346,43 @@ static int (* const ioctl_handlers[])(st
static int dispatch_ioctl(struct client *client,
unsigned int cmd, void __user *arg)
{
union ioctl_arg buffer;
int ret;
if (fw_device_is_shutdown(client->device))
return -ENODEV;
if (_IOC_TYPE(cmd) != '#' ||
_IOC_NR(cmd) >= ARRAY_SIZE(ioctl_handlers))
return -EINVAL;
- if (_IOC_DIR(cmd) & _IOC_WRITE) {
- if (_IOC_SIZE(cmd) > sizeof(buffer) ||
- copy_from_user(&buffer, arg, _IOC_SIZE(cmd)))
+ if (_IOC_SIZE(cmd) > sizeof(buffer))
+ return -EFAULT;
+
+ 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 ...
