[arch-projects] [RFC 13/23] Check device with blkid before cryptsetup create

[Tom Gundersen]

On Fri, May 18, 2012 at 6:22 PM, Matthew Monaco <dgbaley27 at 0x01b.net> wrote:
> Currently in rc.sysinit we check that blkid returns 2 before running
> mkswap. This is a little bit stronger. Even without mkswap "cryptsetup
> create" can be dangerous, so do the blkid check for all plain (non-LUKS)
> mappings. Furthermore, just check for a non-zero return status, if this
> is too broad we can get more specific.

I think you reverted the check. It used to be "if blkid returns 2
overwrite the device" now you do "if blkid returns 0 we can overwrite
the device".

> Note: A user can still destroy her data if she enters the wrong password
> for a cryptsetup create. This we'll leave as the user's fault; she
> should be aware of the limitations of a plain mapping and the
> --verify-passphrase cryptsetup option.
> ---
>  cryptmount.sh |   15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/cryptmount.sh b/cryptmount.sh
> index d602043..03699d0 100755
> --- a/cryptmount.sh
> +++ b/cryptmount.sh
> @@ -1,6 +1,6 @@
>  #!/bin/sh
>
> -SHORTOPTS="LMUc:w:nqvho:O:"
> +SHORTOPTS="LMUc:fw:nqvho:O:"
>  DEPS="cryptsetup blkid findmnt mkswap mktemp"
>  UDEVRUNNING=0
>
> @@ -10,6 +10,7 @@ WAITTIME=10
>  CRYPTTAB=/etc/crypttab
>  OPTIONS=
>  FILTER="!noauto"
> +FORCE=0
>
>  ct_print_usage() {
>        cat <<__EOF__
> @@ -32,6 +33,8 @@ usage: $0 [OPTIONS] [-L]
>
>   options:
>     -c FILE  set the crypttab location (default: /etc/crypttab)
> +    -f       force destructive operations even when a block device appears to
> +             contain data

As this is a bit dangerous stuff, it might be best to not have an -f
option, but rather advice the user to use wipefs manually. Or are
there situations where we really must force cryptsetup, but cannot run
wipefs first?

>     -w NUM   wait time (seconds) for a device if it is not already available
>     -n       dry run
>     -q       decrease verbosity
> @@ -115,6 +118,7 @@ ct_main() {
>                        M) set_action map;;
>                        U) set_action unmap;;
>                        c) CRYPTTAB="$OPTARG";;
> +                       f) FORCE=1;;
>                        w) WAITTIME=${OPTARG//[!0-9]};;
>                        n) DRYRUN=1;;
>                        q) LOGLEVEL=$(( LOGLEVEL - 1 ));;
> @@ -381,7 +385,14 @@ ct_map() {
>
>                info "device '$dev' assumed to be plain"
>
> -               if run cryptsetup create $key $args "$name" "$dev"; then
> +               # cryptsetup 'create' can be destructive, don't do it if blkid can
> +               # identify the device type
> +               if [ $FORCE -ne 1 ] && blkid -p "$dev" &>/dev/null; then
> +                       error "Refusing to call 'cryptsetup create' on device that might"
> +                       error " have data. If you are sure this is what you want, use"
> +                       error " the -f option"
> +                       ret=1
> +               elif run cryptsetup create $key $args "$name" "$dev"; then
>                        info "sucessfully mapped '$dev' to '/dev/mapper/$name'"
>                        if [ $swap -eq 1 ]; then
>                                if run mkswap -f -L "$name" "/dev/mapper/$name"; then
> --
> 1.7.10.2
>