linux-kernel - Re: [PATCH v20 02/20] ipe: add policy parser

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Message-ID: <CAHC9VhQ6ndv4wU4CBBhABHuriPDg=CmBi+_TbjCg+DNsCRuRSA@mail.gmail.com>
Date: Thu, 15 Aug 2024 15:11:24 -0400
From: Paul Moore <paul@...l-moore.com>
To: Fan Wu <wufan@...ux.microsoft.com>, "Serge E. Hallyn" <serge@...lyn.com>
Cc: corbet@....net, zohar@...ux.ibm.com, jmorris@...ei.org, tytso@....edu, 
	ebiggers@...nel.org, axboe@...nel.dk, agk@...hat.com, snitzer@...nel.org, 
	mpatocka@...hat.com, eparis@...hat.com, linux-doc@...r.kernel.org, 
	linux-integrity@...r.kernel.org, linux-security-module@...r.kernel.org, 
	fsverity@...ts.linux.dev, linux-block@...r.kernel.org, 
	dm-devel@...ts.linux.dev, audit@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Deven Bowers <deven.desai@...ux.microsoft.com>
Subject: Re: [PATCH v20 02/20] ipe: add policy parser

On Wed, Aug 14, 2024 at 2:23 PM Fan Wu <wufan@...ux.microsoft.com> wrote:
> On 8/13/2024 6:53 PM, Paul Moore wrote:
> > On Tue, Aug 13, 2024 at 1:54 PM Fan Wu <wufan@...ux.microsoft.com> wrote:
> >> On 8/10/2024 8:50 AM, Serge E. Hallyn wrote:
> >>> On Fri, Aug 02, 2024 at 11:08:16PM -0700, Fan Wu wrote:
> >>>> From: Deven Bowers <deven.desai@...ux.microsoft.com>
> >>>>
> >>>> IPE's interpretation of the what the user trusts is accomplished through
> >>>
> >>> nit: "of what the user trusts" (drop the extra 'the')
> >>>
> >>>> its policy. IPE's design is to not provide support for a single trust
> >>>> provider, but to support multiple providers to enable the end-user to
> >>>> choose the best one to seek their needs.
> >>>>
> >>>> This requires the policy to be rather flexible and modular so that
> >>>> integrity providers, like fs-verity, dm-verity, or some other system,
> >>>> can plug into the policy with minimal code changes.
> >>>>
> >>>> Signed-off-by: Deven Bowers <deven.desai@...ux.microsoft.com>
> >>>> Signed-off-by: Fan Wu <wufan@...ux.microsoft.com>
> >>>
> >>> This all looks fine.  Just one comment below.
> >>>
> >> Thank you for reviewing this!
> >>
> >>>
> >>>> +/**
> >>>> + * parse_rule() - parse a policy rule line.
> >>>> + * @line: Supplies rule line to be parsed.
> >>>> + * @p: Supplies the partial parsed policy.
> >>>> + *
> >>>> + * Return:
> >>>> + * * 0              - Success
> >>>> + * * %-ENOMEM       - Out of memory (OOM)
> >>>> + * * %-EBADMSG      - Policy syntax error
> >>>> + */
> >>>> +static int parse_rule(char *line, struct ipe_parsed_policy *p)
> >>>> +{
> >>>> +    enum ipe_action_type action = IPE_ACTION_INVALID;
> >>>> +    enum ipe_op_type op = IPE_OP_INVALID;
> >>>> +    bool is_default_rule = false;
> >>>> +    struct ipe_rule *r = NULL;
> >>>> +    bool first_token = true;
> >>>> +    bool op_parsed = false;
> >>>> +    int rc = 0;
> >>>> +    char *t;
> >>>> +
> >>>> +    r = kzalloc(sizeof(*r), GFP_KERNEL);
> >>>> +    if (!r)
> >>>> +            return -ENOMEM;
> >>>> +
> >>>> +    INIT_LIST_HEAD(&r->next);
> >>>> +    INIT_LIST_HEAD(&r->props);
> >>>> +
> >>>> +    while (t = strsep(&line, IPE_POLICY_DELIM), line) {
> >>>
> >>> If line is passed in as NULL, t will be NULL on the first test.  Then
> >>> you'll break out and call parse_action(NULL), which calls
> >>> match_token(NULL, ...), which I do not think is safe.
> >>>
> >>> I realize the current caller won't pass in NULL, but it seems worth
> >>> checking for here in case some future caller is added by someone
> >>> who's unaware.
> >>>
> >>> Or, maybe add 'line must not be null' to the function description.
> >>
> >> Yes, I agree that adding a NULL check would be better. I will include it
> >> in the next version.
> >
> > We're still waiting to hear back from the device-mapper devs, but if
> > this is the only change required to the patchset I can add a NULL
> > check when I merge the patchset as it seems silly to resend the entire
> > patchset for this.  Fan, do you want to share the code snippet with
> > the NULL check so Serge can take a look?
>
> Sure, here is the diff.
>
> diff --git a/security/ipe/policy_parser.c b/security/ipe/policy_parser.c
> index 32064262348a..0926b442e32a 100644
> --- a/security/ipe/policy_parser.c
> +++ b/security/ipe/policy_parser.c
> @@ -309,6 +309,9 @@ static int parse_rule(char *line, struct
> ipe_parsed_policy *p)
>          int rc = 0;
>          char *t;
>
> +       if (IS_ERR_OR_NULL(line))
> +               return -EBADMSG;
> +
>          r = kzalloc(sizeof(*r), GFP_KERNEL);
>          if (!r)
>                  return -ENOMEM;
>

Thanks.

Serge, it looks like this should resolve your concern?

-- 
paul-moore.com