Re: var_vacm_access() question

Development documentation goes in the wiki -
http://net-snmp.sourceforge.net/wiki/

  Bill


On Fri, Mar 23, 2018 at 11:46 AM, Keith Mendoza <[email protected]> wrote:

> Bill,
> Thank you for taking the time to explain this to me. Seems to me like
> I should review ASN.1, and MIB-II specs--at the minimum--before
> proceeding any further. Where are dev-related documents usually
> stored? I'd like to contribute my notes once when I'm done.
>
> Thanks,
> Keith
> Thanks,
> Keith
>
>
> On Thu, Mar 22, 2018 at 3:14 PM, Bill Fenner <[email protected]> wrote:
> > The oid represents a request from the user, in which the character
> string is
> > encoded using the SNMP rules. It is converting this OID-encoded string
> into
> > a char* string so that it can look it up in its internal tables.
> >
> >   Bill
> >
> >
> > On Thu, Mar 22, 2018 at 6:13 PM, Keith Mendoza <[email protected]>
> wrote:
> >>
> >> My next question is then, why exactly is it basically copying parts of
> >> an oid into cp and basically truncating parts of it?
> >>
> >> Thanks,
> >> Keith
> >> Thanks,
> >> Keith
> >>
> >>
> >> On Thu, Mar 22, 2018 at 6:47 AM, Bill Fenner <[email protected]> wrote:
> >> > On Wed, Mar 21, 2018 at 5:50 PM, Keith Mendoza <[email protected]>
> >> > wrote:
> >> >>
> >> >> Hi,
> >> >> I'm one of the volunteer developers with ICEI (please see email with
> >> >> subject "ICEI asks what help you need" for details). I was attempting
> >> >> to compile net-snmp code with -std=c99 compiler option, and the
> >> >> compiler failed with "error: overflow in implicit constant conversion
> >> >> [-Werror=overflow] on the following lines in
> >> >> net-snmp-code/agent/mibII/vacm_vars.c: 382, 397, and 593. These 3
> >> >> locations have *cp++ = 255;
> >> >>
> >> >> So, my question is where can I get more information on
> >> >> var_vacm_access(). It appears to me it has something to do with
> >> >> determining group access control for a MIB group. Specifically, what
> >> >> is the rational for incrementing, then basically setting the location
> >> >> pointed by "cp" to 255 given the if logic above each of the 3
> >> >> locations where *cp++ = 255 is set.
> >> >
> >> > Keith,
> >> >
> >> > The blocks in question look like
> >> >
> >> >     oid            *op;
> >> >
> >> >     char           *cp;
> >> >
> >> > ...
> >> >             cp = contextPrefix;
> >> >             for (i = 0; i <= len && op < name + *length; i++) {
> >> >                 if (*op > 255) {
> >> >                     *cp++ = 255;
> >> >                     ++op;
> >> >                 } else
> >> >                     *cp++ = (char) *op++;
> >> >             }
> >> >
> >> > The underlying type of oid is int or long, so it becomes obvious that
> >> > this
> >> > code is copying values from op to cp while truncating values that
> won’t
> >> > fit
> >> > into a char.
> >> >
> >> > It’s probably not unreasonable to change the relevant types to u_char.
> >> >
> >> > Bill
> >
> >
>

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