4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Sabrina Dubroca sd@queasysnail.net
[ Upstream commit c7272c2f1229125f74f22dcdd59de9bbd804f1c8 ]
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/ipv4/route.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
--- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -126,10 +126,13 @@ static int ip_rt_redirect_silence __read static int ip_rt_error_cost __read_mostly = HZ; static int ip_rt_error_burst __read_mostly = 5 * HZ; static int ip_rt_mtu_expires __read_mostly = 10 * 60 * HZ; -static int ip_rt_min_pmtu __read_mostly = 512 + 20 + 20; +static u32 ip_rt_min_pmtu __read_mostly = 512 + 20 + 20; static int ip_rt_min_advmss __read_mostly = 256;
static int ip_rt_gc_timeout __read_mostly = RT_GC_TIMEOUT; + +static int ip_min_valid_pmtu __read_mostly = IPV4_MIN_MTU; + /* * Interface to generic destination cache. */ @@ -2772,7 +2775,8 @@ static struct ctl_table ipv4_route_table .data = &ip_rt_min_pmtu, .maxlen = sizeof(int), .mode = 0644, - .proc_handler = proc_dointvec, + .proc_handler = proc_dointvec_minmax, + .extra1 = &ip_min_valid_pmtu, }, { .procname = "min_adv_mss",