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

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Message-ID: <009001d7170d$e584d360$b08e7a20$@samsung.com>
Date:   Fri, 12 Mar 2021 16:04:08 +0900
From:   이정현 <jhs2.lee@...sung.com>
To:     "'Sami Tolvanen'" <samitolvanen@...gle.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

Hello, Dear Sami Tolvanen.
Thank you for reply.

> 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.

Of course, I don't think this will happen because they are dm-verity experts.
But since we are humans, I think this case could happen accidentally.
So it would be a good at preventing these cases.

> 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"?

Yes of course. That looks better.

I also had some ambiguous about how to express it. 
This is because I couldn't find it in document. 
The code says verity mode, so I wrote it down. never mind it :) 

like this)
    case DM_VERITY_MODE_LOGGING:
    case DM_VERITY_MODE_RESTART:
    case DM_VERITY_MODE_PANIC:


> 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