net: ipv4: add capability check for net administration

Root in init user namespace can modify /proc/sys/net/ipv4/ip_forward
without CAP_NET_ADMIN, this doesn't follow the principle of
capabilities. For example, let's take a look at netdev_store(),
root can't modify netdev attribute without CAP_NET_ADMIN.
So let's keep the consistency of permission check logic.

Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: Yang Yang <yang.yang29@zte.com.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index d38124b..94b648d 100644 (file)
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -2424,11 +2424,15 @@ static int devinet_sysctl_forward(struct ctl_table *ctl, int write,
        int *valp = ctl->data;
        int val = *valp;
        loff_t pos = *ppos;
-       int ret = proc_dointvec(ctl, write, buffer, lenp, ppos);
+       struct net *net = ctl->extra2;
+       int ret;
 
-       if (write && *valp != val) {
-               struct net *net = ctl->extra2;
+       if (write && !ns_capable(net->user_ns, CAP_NET_ADMIN))
+               return -EPERM;
+
+       ret = proc_dointvec(ctl, write, buffer, lenp, ppos);
 
+       if (write && *valp != val) {
                if (valp != &IPV4_DEVCONF_DFLT(net, FORWARDING)) {
                        if (!rtnl_trylock()) {
                                /* Restore the original values before restarting */