net: ipv4: don't allow setting net.ipv4.route.min_pmtu below 68
authorSabrina Dubroca <sd@queasysnail.net>
Mon, 26 Feb 2018 15:13:43 +0000 (16:13 +0100)
committerDavid S. Miller <davem@davemloft.net>
Tue, 27 Feb 2018 16:13:36 +0000 (11:13 -0500)
commitc7272c2f1229125f74f22dcdd59de9bbd804f1c8
tree4f70a439a495a90316a1ba294b9ddadcbf7cf292
parent68b116a28f359c6d60b86af33a3f7c1f319542e4
net: ipv4: don't allow setting net.ipv4.route.min_pmtu below 68

According to RFC 1191 sections 3 and 4, ICMP frag-needed messages
indicating an MTU below 68 should be rejected:

    A host MUST never reduce its estimate of the Path MTU below 68
    octets.

and (talking about ICMP frag-needed's Next-Hop MTU field):

    This field will never contain a value less than 68, since every
    router "must be able to forward a datagram of 68 octets without
    fragmentation".

Furthermore, by letting net.ipv4.route.min_pmtu be set to negative
values, we can end up with a very large PMTU when (-1) is cast into u32.

Let's also make ip_rt_min_pmtu a u32, since it's only ever compared to
unsigned ints.

Reported-by: Jianlin Shi <jishi@redhat.com>
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Reviewed-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
net/ipv4/route.c