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Introduce a sysctl that modifies the value of PROT_SOCK.

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Add net.ipv4.ip_unprivileged_port_start, which is a per namespace sysctl
that denotes the first unprivileged inet port in the namespace.  To
disable all privileged ports set this to zero.  It also checks for
overlap with the local port range.  The privileged and local range may
not overlap.

The use case for this change is to allow containerized processes to bind
to priviliged ports, but prevent them from ever being allowed to modify
their container's network configuration.  The latter is accomplished by
ensuring that the network namespace is not a child of the user
namespace.  This modification was needed to allow the container manager
to disable a namespace's priviliged port restrictions without exposing
control of the network namespace to processes in the user namespace.

Signed-off-by: Krister Johansen <kjlx@templeofstupid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Krister Johansen 2017-01-20 17:49:11 -08:00 • committed by David S. Miller
parent d140199af5
commit 4548b683b7
9 changed files with 86 additions and 12 deletions
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5
net/ipv4/af_inet.c
View file

@ -479,7 +479,7 @@ int inet_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
snum = ntohs(addr->sin_port);
err = -EACCES;
if (snum && snum < PROT_SOCK &&
if (snum && snum < inet_prot_sock(net) &&
!ns_capable(net->user_ns, CAP_NET_BIND_SERVICE))
goto out;
@ -1700,6 +1700,9 @@ static __net_init int inet_init_net(struct net *net)
net->ipv4.sysctl_ip_default_ttl = IPDEFTTL;
net->ipv4.sysctl_ip_dynaddr = 0;
net->ipv4.sysctl_ip_early_demux = 1;
#ifdef CONFIG_SYSCTL
net->ipv4.sysctl_ip_prot_sock = PROT_SOCK;
#endif
return 0;
}