On 3/21/17 11:53 AM, Toomas Soome wrote:
On 21. märts 2017, at 17:15, Ian Lepore <i...@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;)
All the world is not an VAX, nor is every network Ethernet.
HIPPI, not that you see much of it nowadays, had a MTU for
switched networks of 65280 (64K - 216 bytes of overhead).
Using USHRT_MAX is exactly the right thing here.
-Kurt
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