Re: [dpdk-dev] [PATCH] rte_ether: force format string for unformat_addr

[Stephen Hemminger <stephen@networkplumber.org>]

On Wed, 10 Jul 2019 16:31:59 -0400
Aaron Conole <aconole@redhat.com> wrote:

> Stephen Hemminger <stephen@networkplumber.org> writes:
> 
> > On Wed, 10 Jul 2019 15:13:02 -0400
> > Aaron Conole <aconole@redhat.com> wrote:
> >  
> >> Stephen Hemminger <stephen@networkplumber.org> writes:
> >>   
> >> > On Wed, 10 Jul 2019 14:33:42 -0400
> >> > Aaron Conole <aconole@redhat.com> wrote:
> >> >    
> >> >> rte_ether_unformation_addr is very lax in what it accepts now, including
> >> >> ethernet addresses formatted ambiguously as "x:xx:x:xx:x:xx".  However,
> >> >> previously this behavior was enforced via the my_ether_aton which would
> >> >> fail ambiguously formatted values.
> >> >> 
> >> >> Reported-by: Michael Santana <msantana@redhat.com>
> >> >> Fixes: 596d31092d32 ("net: add function to convert string to ethernet address")
> >> >> Signed-off-by: Aaron Conole <aconole@redhat.com>
> >> >> ---
> >> >>  lib/librte_net/rte_ether.c | 6 ++++--
> >> >>  1 file changed, 4 insertions(+), 2 deletions(-)
> >> >> 
> >> >> diff --git a/lib/librte_net/rte_ether.c b/lib/librte_net/rte_ether.c
> >> >> index 8d040173c..4f252b813 100644
> >> >> --- a/lib/librte_net/rte_ether.c
> >> >> +++ b/lib/librte_net/rte_ether.c
> >> >> @@ -45,7 +45,8 @@ rte_ether_unformat_addr(const char *s, struct rte_ether_addr *ea)
> >> >>  	if (n == 6) {
> >> >>  		/* Standard format XX:XX:XX:XX:XX:XX */
> >> >>  		if (o0 > UINT8_MAX || o1 > UINT8_MAX || o2 > UINT8_MAX ||
> >> >> -		    o3 > UINT8_MAX || o4 > UINT8_MAX || o5 > UINT8_MAX) {
> >> >> +		    o3 > UINT8_MAX || o4 > UINT8_MAX || o5 > UINT8_MAX ||
> >> >> +		    strlen(s) != RTE_ETHER_ADDR_FMT_SIZE - 1) {
> >> >>  			rte_errno = ERANGE;
> >> >>  			return -1;
> >> >>  		}
> >> >> @@ -58,7 +59,8 @@ rte_ether_unformat_addr(const char *s, struct rte_ether_addr *ea)
> >> >>  		ea->addr_bytes[5] = o5;
> >> >>  	} else if (n == 3) {
> >> >>  		/* Support the format XXXX:XXXX:XXXX */
> >> >> -		if (o0 > UINT16_MAX || o1 > UINT16_MAX || o2 > UINT16_MAX) {
> >> >> +		if (o0 > UINT16_MAX || o1 > UINT16_MAX || o2 > UINT16_MAX ||
> >> >> +		    strlen(s) != RTE_ETHER_ADDR_FMT_SIZE - 4) {
> >> >>  			rte_errno = ERANGE;
> >> >>  			return -1;
> >> >>  		}    
> >> >
> >> > NAK
> >> > Skipping leading zero should be ok. There is no need for this patch.    
> >> 
> >> Is it intended to skip the leading 0?  Why not the trailing 0?  I'm not
> >> familiar with the format that is used here  (example - X:XX:X:XX:X)
> >> 
> >> It isn't described in any RFC I could find (but I only did a small
> >> search).  Even in IEEE, the format is always a full octet.
> >>   
> >> > The current behavior is superset of what standard ether_aton accepts.    
> >> 
> >> Okay, but it introduces a test failure for the cmdline tests and then
> >> that test will need a few lines removed for 'unsuccessful' formats.
> >> 
> >> ether_aton is much more rigid in the formats it accepts, so the test
> >> case is enforcing that.  I guess either the current behavior of this
> >> function changes (and since it is a new behavior of the cmdline parser,
> >> I would think it should be changed) or the test case should be changed
> >> to adopt it.  
> >
> > BSD ether_aton is:
> > /*
> >  * Convert an ASCII representation of an ethernet address to binary form.
> >  */
> > struct ether_addr *
> > ether_aton_r(const char *a, struct ether_addr *e)
> > {
> > 	int i;
> > 	unsigned int o0, o1, o2, o3, o4, o5;
> >
> > 	i = sscanf(a, "%x:%x:%x:%x:%x:%x", &o0, &o1, &o2, &o3, &o4, &o5);
> > 	if (i != 6)
> > 		return (NULL);
> > 	e->octet[0]=o0;
> > 	e->octet[1]=o1;
> > 	e->octet[2]=o2;
> > 	e->octet[3]=o3;
> > 	e->octet[4]=o4;
> > 	e->octet[5]=o5;
> > 	return (e);
> > }  
> 
> Your implementation fixes the above by bounds checking each octet
> to enforce that in the 6-octet form, each octet is bound to the region
> 00-ff.
> 
> The BSD example only accepts a 6-octet form.  Your version is intended
> to accept both colon forms so x:x:x will successfully parse as well
> (interpreted on the XXXX:XXXX:XXXX side) (ie: mac 02:03:04 or 2:3:4
> would be accepted).  Further, accidentally passing an ipv6 address to
> this routine (something a user of a cmdline interface might do) could be
> parsed as valid (example: 2001:db8:2::1) - which would be the wrong
> thing.  I think it would be strange for length limits to be enforced in
> cmdline parser *after* calling this, but that might be an option for
> fixing (so patch cmdline_parse_etheraddr to do a length check after the
> unformat_addr call).

Being liberal in what you accept as input is a good core principle.
BSD goes too far, but what you propose is too restrictive.

> I guess I'm not sure what the *best* fix would be.  I think the most
> sane fix is what I've put in since it will only allow the commonly
> accepted notation, and not allow ad-hoc accidents.  Higher layers (like
> cmdline parsers) are free to implement routines that reformat the lax
> forms (like you might want to allow a user to pass) into more
> restrictive forms required by a lower layer (like librte_net).  I
> concede that there could be a more friendly thing to do in some specific
> cases - but then we must more strictly validate the *form* (ie: we
> have a scanf where one form is a subset of another and will be okay with
> some kinds of invalid characters being inserted - allowing for things
> like IPV6 addresses looking like ethernet hardware addresses).

Fix the cmdline test.