ipv6 addrconf: remove addrconf_sysctl_hop_limit()

This is an effective no-op in terms of user observable behaviour.

By preventing the overwrite of non-null extra1/extra2 fields
in addrconf_sysctl() we can enable the use of proc_dointvec_minmax().

This allows us to eliminate the constant min/max (1..255) trampoline
function that is addrconf_sysctl_hop_limit().

This is nice because it simplifies the code, and allows future
sysctls with constant min/max limits to also not require trampolines.

We still can't eliminate the trampoline for mtu because it isn't
actually a constant (it depends on other tunables of the device)
and thus requires at-write-time logic to enforce range.

Signed-off-by: Maciej Żenczykowski <maze@google.com>
Acked-by: Erik Kline <ek@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 8718398..cbd9343 100644 (file)
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -5496,20 +5496,6 @@ int addrconf_sysctl_forward(struct ctl_table *ctl, int write,
        return ret;
 }
 
-static
-int addrconf_sysctl_hop_limit(struct ctl_table *ctl, int write,
-                              void __user *buffer, size_t *lenp, loff_t *ppos)
-{
-       struct ctl_table lctl;
-       int min_hl = 1, max_hl = 255;
-
-       lctl = *ctl;
-       lctl.extra1 = &min_hl;
-       lctl.extra2 = &max_hl;
-
-       return proc_dointvec_minmax(&lctl, write, buffer, lenp, ppos);
-}
-
 static
 int addrconf_sysctl_mtu(struct ctl_table *ctl, int write,
                        void __user *buffer, size_t *lenp, loff_t *ppos)
@@ -5743,6 +5729,9 @@ int addrconf_sysctl_ignore_routes_with_linkdown(struct ctl_table *ctl,
        return ret;
 }
 
+static const int one = 1;
+static const int two_five_five = 255;
+
 static const struct ctl_table addrconf_sysctl[] = {
        {
                .procname       = "forwarding",
@@ -5756,7 +5745,9 @@ static const struct ctl_table addrconf_sysctl[] = {
                .data           = &ipv6_devconf.hop_limit,
                .maxlen         = sizeof(int),
                .mode           = 0644,
-               .proc_handler   = addrconf_sysctl_hop_limit,
+               .proc_handler   = proc_dointvec_minmax,
+               .extra1         = (void *)&one,
+               .extra2         = (void *)&two_five_five,
        },
        {
                .procname       = "mtu",
@@ -6081,8 +6072,14 @@ static int __addrconf_sysctl_register(struct net *net, char *dev_name,
 
        for (i = 0; table[i].data; i++) {
                table[i].data += (char *)p - (char *)&ipv6_devconf;
-               table[i].extra1 = idev; /* embedded; no ref */
-               table[i].extra2 = net;
+               /* If one of these is already set, then it is not safe to
+                * overwrite either of them: this makes proc_dointvec_minmax
+                * usable.
+                */
+               if (!table[i].extra1 && !table[i].extra2) {
+                       table[i].extra1 = idev; /* embedded; no ref */
+                       table[i].extra2 = net;
+               }
        }
 
        snprintf(path, sizeof(path), "net/ipv6/conf/%s", dev_name);