inet: frag: set limits and make init_net's high_thresh limit global

This patch makes init_net's high_thresh limit to be the maximum for all
namespaces, thus introducing a global memory limit threshold equal to the
sum of the individual high_thresh limits which are capped.
It also introduces some sane minimums for low_thresh as it shouldn't be
able to drop below 0 (or > high_thresh in the unsigned case), and
overall low_thresh should not ever be above high_thresh, so we make the
following relations for a namespace:
init_net:
 high_thresh - max(not capped), min(init_net low_thresh)
 low_thresh - max(init_net high_thresh), min (0)

all other namespaces:
 high_thresh = max(init_net high_thresh), min(namespace's low_thresh)
 low_thresh = max(namespace's high_thresh), min(0)

The major issue with having low_thresh > high_thresh is that we'll
schedule eviction but never evict anything and thus rely only on the
timers.

Signed-off-by: Nikolay Aleksandrov <nikolay@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 2 deletions

diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c
index ccee68dffd6e..634fc31aa243 100644
--- a/net/ipv4/ip_fragment.c
+++ b/net/ipv4/ip_fragment.c
@@ -700,14 +700,17 @@ static struct ctl_table ip4_frags_ns_ctl_table[] = {
                 .data           = &init_net.ipv4.frags.high_thresh,
                 .maxlen         = sizeof(int),
                 .mode           = 0644,
-                .proc_handler   = proc_dointvec
+                .proc_handler   = proc_dointvec_minmax,
+                .extra1         = &init_net.ipv4.frags.low_thresh
         },
         {
                 .procname       = "ipfrag_low_thresh",
                 .data           = &init_net.ipv4.frags.low_thresh,
                 .maxlen         = sizeof(int),
                 .mode           = 0644,
-                .proc_handler   = proc_dointvec
+                .proc_handler   = proc_dointvec_minmax,
+                .extra1         = &zero,
+                .extra2         = &init_net.ipv4.frags.high_thresh
         },
         {
                 .procname       = "ipfrag_time",
@@ -752,7 +755,10 @@ static int __net_init ip4_frags_ns_ctl_register(struct net *net)
                         goto err_alloc;
 
                 table[0].data = &net->ipv4.frags.high_thresh;
+                table[0].extra1 = &net->ipv4.frags.low_thresh;
+                table[0].extra2 = &init_net.ipv4.frags.high_thresh;
                 table[1].data = &net->ipv4.frags.low_thresh;
+                table[1].extra2 = &net->ipv4.frags.high_thresh;
                 table[2].data = &net->ipv4.frags.timeout;
 
                 /* Don't export sysctls to unprivileged users */