Re: [Linux-kernel-mentees] [PATCH v3] media/v4l2-core: Fix kernel-infoleak in video_put_user()

[Dan Carpenter <dan.carpenter@oracle.com>]

On Mon, Jul 27, 2020 at 06:33:57PM -0400, Peilin Ye wrote:
> On Mon, Jul 27, 2020 at 04:16:08PM +0300, Dan Carpenter wrote:
> > drivers/block/floppy.c:3132 raw_cmd_copyout() warn: check that 'cmd' doesn't leak information (struct has a hole after 'flags')
> 
> (Removed some Cc: recipients from the list.)
> 
> I'm not very sure, but I think this one is also a false positive.

No, it's a potential bug.  You're over thinking what Smatch is
complaining about.  Arnd is right.

  3123  static int raw_cmd_copyout(int cmd, void __user *param,
  3124                                    struct floppy_raw_cmd *ptr)
  3125  {
  3126          int ret;
  3127  
  3128          while (ptr) {
  3129                  struct floppy_raw_cmd cmd = *ptr;
                                              ^^^^^^^^^^
The compiler can either do this assignment as an memcpy() or as a
series of struct member assignments.  So the assignment can leave the
struct hole uninitialized.

  3130                  cmd.next = NULL;
  3131                  cmd.kernel_data = NULL;
  3132                  ret = copy_to_user(param, &cmd, sizeof(cmd));
                                                  ^^^^
potential info leak.

  3133                  if (ret)
  3134                          return -EFAULT;
  3135                  param += sizeof(struct floppy_raw_cmd);
  3136                  if ((ptr->flags & FD_RAW_READ) && ptr->buffer_length) {
  3137                          if (ptr->length >= 0 &&
  3138                              ptr->length <= ptr->buffer_length) {
  3139                                  long length = ptr->buffer_length - ptr->length;
  3140                                  ret = fd_copyout(ptr->data, ptr->kernel_data,
  3141                                                   length);
  3142                                  if (ret)
  3143                                          return ret;
  3144                          }
  3145                  }
  3146                  ptr = ptr->next;
  3147          }
  3148  
  3149          return 0;
  3150  }

regards,
dan carpenter