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SubjectRe: [PATCH] ima: drop vla in ima_audit_measurement()
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On Thu, 2018-03-08 at 12:04 -0700, Tycho Andersen wrote:
> On Thu, Mar 08, 2018 at 01:50:30PM -0500, Mimi Zohar wrote:
> > On Thu, 2018-03-08 at 11:37 -0700, Tycho Andersen wrote:
> > > On Thu, Mar 08, 2018 at 07:47:37PM +0200, Andy Shevchenko wrote:
> > > > On Thu, Mar 8, 2018 at 7:14 PM, Tycho Andersen <tycho@tycho.ws> wrote:
> > > > > In keeping with the directive to get rid of VLAs [1], let's drop the VLA
> > > > > from ima_audit_measurement(). We need to adjust the return type of
> > > > > ima_audit_measurement, because now this function can fail if an allocation
> > > > > fails.
> > > >
> > > >
> > > >
> > > > > + algo_hash_len = hash_len + strlen(algo_name) + 2;
> > > > > + algo_hash = kzalloc(algo_hash_len, GFP_KERNEL);
> > > >
> > > > > - snprintf(algo_hash, sizeof(algo_hash), "%s:%s", algo_name, hash);
> > > > > + snprintf(algo_hash, algo_hash_len, "%s:%s", algo_name, hash);
> > > >
> > > > kasprintf() ?
> > >
> > > Sure, in fact I think we could just do:
> > >
> > > - snprintf(algo_hash, algo_hash_len, "%s:%s", algo_name, hash);
> > > - audit_log_untrustedstring(ab, algo_hash);
> > > + audit_log_untrustedstring(ab, algo_name);
> > > + audit_log_format(ab, ":");
> > > + audit_log_untrustedstring(ab, hash);
> > >
> > > and get rid of the allocation entirely. I'll test and make sure it
> > > works and then re-send.
> >
> > The hash algorithm name is an enumeration that comes from the kernel.
> >  It's defined in crypto/hash_info.c: hash_algo_name.  Why do we need
> > to use audit_log_untrustedstring()?
>
> Yes, I suppose we don't need it for the hash either, since we're
> generating that and we know it's just hex digits and not any audit
> control characters or "s or anything.
>
> It looks like we could get rid of the other allocation too by just
> using audit_log_n_hex, but that uses hex_byte_pack_upper, vs. the
> hex_byte_pack that's currently in use in this function. Is that too
> much of a breakage?

Based on the discussion with Richard Briggs, we need to differentiate
between the ima_audit_measurement() and the ima_parse_rule() usage of
AUDIT_INTEGRITY_RULE.  The ima_parse_rule() will continue to use
AUDIT_INTEGRITY_RULE.  ima_audit_measurement() will need to define and
use a new number.  Auidt name suggestions would be appreciated.

When we make that sort of change, any other changes are insignificant.
How different are the two formats?

Mimi

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