linux-kernel - Re: [PATCH 2/2] dm verity: allow only one verify mode

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Date:   Thu, 11 Mar 2021 14:34:56 -0800
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     JeongHyeon Lee <jhs2.lee@...sung.com>
Cc:     Mike Snitzer <snitzer@...hat.com>,
        Alasdair Kergon <agk@...hat.com>,
        device-mapper development <dm-devel@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] dm verity: allow only one verify mode

On Thu, Mar 11, 2021 at 4:19 AM JeongHyeon Lee <jhs2.lee@...sung.com> wrote:
>
> If there are multiple verity mode when parsing the verity mode of dm
> verity table, it will be set as the last one.
> So set to 'allow only once' to prevent it.

I agree that we shouldn't allow this, at least not without a warning,
but out of curiosity, do you actually have a situation where this
could happen? One ideally shouldn't be passing untrusted parameters to
dm-verity.

>
> Signed-off-by: JeongHyeon Lee <jhs2.lee@...sung.com>
> ---
>  drivers/md/dm-verity-target.c | 38 ++++++++++++++++++++++++++---------
>  1 file changed, 28 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
> index 808a98ef624c..b76431dc7721 100644
> --- a/drivers/md/dm-verity-target.c
> +++ b/drivers/md/dm-verity-target.c
> @@ -893,6 +893,28 @@ static int verity_alloc_zero_digest(struct dm_verity *v)
>         return r;
>  }
>
> +static inline bool verity_is_verity_mode(const char *arg_name)
> +{
> +       return (!strcasecmp(arg_name, DM_VERITY_OPT_LOGGING) ||
> +               !strcasecmp(arg_name, DM_VERITY_OPT_RESTART) ||
> +               !strcasecmp(arg_name, DM_VERITY_OPT_PANIC));
> +}
> +
> +static int verity_parse_verity_mode(struct dm_verity *v, const char *arg_name)
> +{
> +       if (v->mode)
> +               return -EINVAL;
> +
> +       if (!strcasecmp(arg_name, DM_VERITY_OPT_LOGGING))
> +               v->mode = DM_VERITY_MODE_LOGGING;
> +       else if (!strcasecmp(arg_name, DM_VERITY_OPT_RESTART))
> +               v->mode = DM_VERITY_MODE_RESTART;
> +       else if (!strcasecmp(arg_name, DM_VERITY_OPT_PANIC))
> +               v->mode = DM_VERITY_MODE_PANIC;
> +
> +       return 0;
> +}
> +
>  static int verity_parse_opt_args(struct dm_arg_set *as, struct dm_verity *v,
>                                  struct dm_verity_sig_opts *verify_args)
>  {
> @@ -916,16 +938,12 @@ static int verity_parse_opt_args(struct dm_arg_set *as, struct dm_verity *v,
>                 arg_name = dm_shift_arg(as);
>                 argc--;
>
> -               if (!strcasecmp(arg_name, DM_VERITY_OPT_LOGGING)) {
> -                       v->mode = DM_VERITY_MODE_LOGGING;
> -                       continue;
> -
> -               } else if (!strcasecmp(arg_name, DM_VERITY_OPT_RESTART)) {
> -                       v->mode = DM_VERITY_MODE_RESTART;
> -                       continue;
> -
> -               } else if (!strcasecmp(arg_name, DM_VERITY_OPT_PANIC)) {
> -                       v->mode = DM_VERITY_MODE_PANIC;
> +               if (verity_is_verity_mode(arg_name)) {
> +                       r = verity_parse_verity_mode(v, arg_name);
> +                       if (r) {
> +                               ti->error = "Already verity mode set";

I don't have a strong opinion about this, but the documentation
doesn't talk about verity modes, so perhaps this could be reworded to
something like "Conflicting error handling parameters"?

> +                               return r;
> +                       }
>                         continue;
>
>                 } else if (!strcasecmp(arg_name, DM_VERITY_OPT_IGN_ZEROES)) {
> --
> 2.17.1
>

Sami