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    Subject[PATCH 4.14 041/110] net: ipv4: dont allow setting net.ipv4.route.min_pmtu below 68
    Date
    4.14-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
    @@ -128,10 +128,13 @@ 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.
    */
    @@ -2934,7 +2937,8 @@ 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",

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