svn commit: r315653 - in head: lib/libstand sys/boot/common sys/boot/i386/libi386

[Slawa Olhovchenkov]

On Tue, Mar 21, 2017 at 05:53:12PM +0200, Toomas Soome wrote:

> 
> > On 21. märts 2017, at 17:15, Ian Lepore <ian at freebsd.org> wrote:
> > 
> > On Tue, 2017-03-21 at 15:35 +0300, Slawa Olhovchenkov wrote:
> >> On Mon, Mar 20, 2017 at 10:20:17PM +0000, Toomas Soome wrote:
> >> 
> >>> 
> >>> Author: tsoome
> >>> Date: Mon Mar 20 22:20:17 2017
> >>> New Revision: 315653
> >>> URL: https://svnweb.freebsd.org/changeset/base/315653
> >>> 
> >>> Log:
> >>>   loader: verify the value from dhcp.interface-mtu and use snprintf
> >>> to set mtu
> >>>   
> >>>   Since the uset can set dhcp.interface-mtu, we need to try to
> >>> validate the
> >>>   value. So we verify if the conversion to int is successful and we
> >>> will not
> >>>   allow to set value greater than max IPv4 packet size.
> >>>   
> >>> +				    tmp > USHRT_MAX) {
> >>> +					printf("%s: bad value:
> >>> \"%s\", "
> >>> +					    "ignoring\n",
> >>> +					    "dhcp.interface-mtu",
> >>> val);
> >> ===
> >> USHRT_MAX	Maximum value for an object of type unsigned short
> >> int
> >> 65535 (216-1) or greater*
> >> 
> >> * the actual value depends on the particular system and library
> >> implementation, but shall reflect the limits of these types in the
> >> target platform.
> >> ===
> >> 
> >> I mean IF_MAXMTU more correct.
> >> 
> > 
> > The context here is libstand; because it is standalone by design, the
> > code doesn't have access to IF_MAXMTU or other kernel/userland
> > constants.  There is also no question that a short is 16 bits or that
> > USHRT_MAX will be anything other than 65535 in that environment.  If
> > some platform did appear that had a different-sized short by default,
> > we would add whatever flags are necessary to force it back to 16 bits
> > in src/share/mk/bsd.stand.mk.
> > 
> 
> 
> Also note the “upper” value is entirely fictional - we felt we need to pick some “sane” default, with current (common 1Gb/s) ethernet hardware you will be in trouble long before reaching that value;)

18000?
IMHO, max found in different spec is about 16K.
Mostly jumbo is 9000-9198.