Re: [PATCH] scsi: 3w-9xxx: fix a missing-check bug

[adam radford]

On Sat, May 5, 2018 at 8:43 PM, Wenwen Wang <wang6495@xxxxxxx> wrote:
> In twa_chrdev_ioctl(), the ioctl driver command is firstly copied from the
> userspace pointer 'argp' and saved to the kernel object 'driver_command'.
> Then a security check is performed on the data buffer size indicated by
> 'driver_command', which is 'driver_command.buffer_length'. If the security
> check is passed, the entire ioctl command is copied again from the 'argp'
> pointer and saved to the kernel object 'tw_ioctl'. Then, various operations
> are performed on 'tw_ioctl' according to the 'cmd'. Given that the 'argp'
> pointer resides in userspace, a malicious userspace process can race to
> change the buffer size between the two copies. This way, the user can
> bypass the security check and inject invalid data buffer size. This can
> cause potential security issues in the following execution.
>
> This patch checks the buffer size obtained in the second copy. An error
> code -EINVAL will be returned if it is not same as the original one in the
> first copy.
>
> Signed-off-by: Wenwen Wang <wang6495@xxxxxxx>
> ---
>  drivers/scsi/3w-9xxx.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/drivers/scsi/3w-9xxx.c b/drivers/scsi/3w-9xxx.c
> index b42c9c4..8bc43db 100644
> --- a/drivers/scsi/3w-9xxx.c
> +++ b/drivers/scsi/3w-9xxx.c
> @@ -684,6 +684,12 @@ static long twa_chrdev_ioctl(struct file *file, unsigned int cmd, unsigned long
>         if (copy_from_user(tw_ioctl, argp, driver_command.buffer_length + sizeof(TW_Ioctl_Buf_Apache) - 1))
>                 goto out3;
>
> +       if (tw_ioctl->driver_command.buffer_length
> +                != driver_command.buffer_length) {
> +               retval = TW_IOCTL_ERROR_OS_EINVAL;
> +               goto out3;
> +       }
> +
>         /* See which ioctl we are doing */
>         switch (cmd) {
>         case TW_IOCTL_FIRMWARE_PASS_THROUGH:
> --
> 2.7.4
>

Drop this patch and create a new one that checks for:  if
!capable(CAP_SYS_ADMIN) in twa_chrdev_ioctl() (like 3w-sas.c does) and
I'll ack it.

-Adam