This is a note to let you know that I've just added the patch titled

net: ipv4: don't allow setting net.ipv4.route.min_pmtu below 68

to the 3.18-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: net-ipv4-don-t-allow-setting-net.ipv4.route.min_pmtu-below-68.patch and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From foo@baz Thu Mar 8 10:42:32 PST 2018

From: Sabrina Dubroca sd@queasysnail.net Date: Mon, 26 Feb 2018 16:13:43 +0100 Subject: net: ipv4: don't allow setting net.ipv4.route.min_pmtu below 68

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 | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -122,9 +122,11 @@ 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_min_valid_pmtu __read_mostly = IPV4_MIN_MTU; + /* * Interface to generic destination cache. */ @@ -2629,7 +2631,8 @@ 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",

Patches currently in stable-queue which might be from sd@queasysnail.net are

queue-3.18/net-ipv4-don-t-allow-setting-net.ipv4.route.min_pmtu-below-68.patch