Re: var_vacm_access() question

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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