Re: [PATCH RFC] btrfs: harden agaist duplicate fsid

[Anand Jain <anand.jain@oracle.com>]

On 11/13/2018 11:31 PM, David Sterba wrote:
> On Mon, Oct 01, 2018 at 09:31:04PM +0800, Anand Jain wrote:
>>>> +        /*
>>>> +         * we are going to replace the device path, make sure its the
>>>> +         * same device if the device mounted
>>>> +         */
>>>> +        if (device->bdev) {
>>>> +            struct block_device *path_bdev;
>>>> +
>>>> +            path_bdev = lookup_bdev(path);
>>>> +            if (IS_ERR(path_bdev)) {
>>>> +                mutex_unlock(&fs_devices->device_list_mutex);
>>>> +                return ERR_CAST(path_bdev);
>>>> +            }
>>>> +
>>>> +            if (device->bdev != path_bdev) {
>>>> +                bdput(path_bdev);
>>>> +                mutex_unlock(&fs_devices->device_list_mutex);
>>>> +                return ERR_PTR(-EEXIST);
>>> It would be _really_ nice to have an informative error message printed
>>> here.  Aside from the possibility of an admin accidentally making a
>>> block-level copy of the volume,
>>
>>> this code triggering could represent an
>>> attempted attack against the system, so it's arguably something that
>>> should be reported as happening.
>>
>>>    Personally, I think a WARN_ON_ONCE for
>>> this would make sense, ideally per-volume if possible.
>>
>>    Ah. Will add an warn. Thanks, Anand
> 
> The requested error message is not in the patch you posted or I have
> missed that (https://patchwork.kernel.org/patch/10641041/) .

  No you didn't miss. I missed it. When you integrated this into
  for-next, I should have sent out v2. Sorry. Thanks for taking
  care of it.

> Austin, is the following ok for you?
> 
>    "BTRFS: duplicate device fsid:devid for %pU:%llu old:%s new:%s\n"
> 
>    BTRFS: duplicate device fsid:devid 7c667b96-59eb-43ad-9ae9-c878f6ad51d8:2 old:/dev/sda6 new:/dev/sdb6
> 
> As the UUID and paths are long I tried to squeeeze the rest so it's
> still comprehensible but this would be better confirmed. Thanks.

Thanks, Anand