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![Jonathon Reinhart](/assets/img/avatar_default.png)
This adds an ensure_safe_net_sysctl() check during register_net_sysctl() to validate that sysctl table entries for a non-init_net netns are sufficiently isolated. To be netns-safe, an entry must adhere to at least (and usually exactly) one of these rules: 1. It is marked read-only inside the netns. 2. Its data pointer does not point to kernel/module global data. An entry which fails both of these checks is indicative of a bug, whereby a child netns can affect global net sysctl values. If such an entry is found, this code will issue a warning to the kernel log, and force the entry to be read-only to prevent a leak. To test, simply create a new netns: $ sudo ip netns add dummy As it sits now, this patch will WARN for two sysctls which will be addressed in a subsequent patch: - /proc/sys/net/netfilter/nf_conntrack_max - /proc/sys/net/netfilter/nf_conntrack_expect_max Signed-off-by: Jonathon Reinhart <Jonathon.Reinhart@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
177 lines
4.4 KiB
C
177 lines
4.4 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/* -*- linux-c -*-
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* sysctl_net.c: sysctl interface to net subsystem.
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*
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* Begun April 1, 1996, Mike Shaver.
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* Added /proc/sys/net directories for each protocol family. [MS]
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*
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* Revision 1.2 1996/05/08 20:24:40 shaver
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* Added bits for NET_BRIDGE and the NET_IPV4_ARP stuff and
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* NET_IPV4_IP_FORWARD.
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*
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*
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*/
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#include <linux/mm.h>
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#include <linux/export.h>
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#include <linux/sysctl.h>
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#include <linux/nsproxy.h>
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#include <net/sock.h>
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#ifdef CONFIG_INET
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#include <net/ip.h>
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#endif
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#ifdef CONFIG_NET
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#include <linux/if_ether.h>
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#endif
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static struct ctl_table_set *
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net_ctl_header_lookup(struct ctl_table_root *root)
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{
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return ¤t->nsproxy->net_ns->sysctls;
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}
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static int is_seen(struct ctl_table_set *set)
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{
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return ¤t->nsproxy->net_ns->sysctls == set;
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}
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/* Return standard mode bits for table entry. */
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static int net_ctl_permissions(struct ctl_table_header *head,
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struct ctl_table *table)
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{
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struct net *net = container_of(head->set, struct net, sysctls);
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/* Allow network administrator to have same access as root. */
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if (ns_capable_noaudit(net->user_ns, CAP_NET_ADMIN)) {
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int mode = (table->mode >> 6) & 7;
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return (mode << 6) | (mode << 3) | mode;
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}
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return table->mode;
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}
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static void net_ctl_set_ownership(struct ctl_table_header *head,
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struct ctl_table *table,
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kuid_t *uid, kgid_t *gid)
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{
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struct net *net = container_of(head->set, struct net, sysctls);
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kuid_t ns_root_uid;
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kgid_t ns_root_gid;
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ns_root_uid = make_kuid(net->user_ns, 0);
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if (uid_valid(ns_root_uid))
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*uid = ns_root_uid;
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ns_root_gid = make_kgid(net->user_ns, 0);
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if (gid_valid(ns_root_gid))
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*gid = ns_root_gid;
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}
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static struct ctl_table_root net_sysctl_root = {
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.lookup = net_ctl_header_lookup,
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.permissions = net_ctl_permissions,
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.set_ownership = net_ctl_set_ownership,
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};
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static int __net_init sysctl_net_init(struct net *net)
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{
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setup_sysctl_set(&net->sysctls, &net_sysctl_root, is_seen);
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return 0;
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}
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static void __net_exit sysctl_net_exit(struct net *net)
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{
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retire_sysctl_set(&net->sysctls);
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}
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static struct pernet_operations sysctl_pernet_ops = {
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.init = sysctl_net_init,
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.exit = sysctl_net_exit,
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};
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static struct ctl_table_header *net_header;
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__init int net_sysctl_init(void)
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{
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static struct ctl_table empty[1];
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int ret = -ENOMEM;
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/* Avoid limitations in the sysctl implementation by
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* registering "/proc/sys/net" as an empty directory not in a
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* network namespace.
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*/
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net_header = register_sysctl("net", empty);
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if (!net_header)
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goto out;
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ret = register_pernet_subsys(&sysctl_pernet_ops);
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if (ret)
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goto out1;
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out:
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return ret;
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out1:
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unregister_sysctl_table(net_header);
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net_header = NULL;
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goto out;
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}
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/* Verify that sysctls for non-init netns are safe by either:
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* 1) being read-only, or
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* 2) having a data pointer which points outside of the global kernel/module
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* data segment, and rather into the heap where a per-net object was
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* allocated.
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*/
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static void ensure_safe_net_sysctl(struct net *net, const char *path,
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struct ctl_table *table)
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{
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struct ctl_table *ent;
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pr_debug("Registering net sysctl (net %p): %s\n", net, path);
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for (ent = table; ent->procname; ent++) {
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unsigned long addr;
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const char *where;
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pr_debug(" procname=%s mode=%o proc_handler=%ps data=%p\n",
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ent->procname, ent->mode, ent->proc_handler, ent->data);
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/* If it's not writable inside the netns, then it can't hurt. */
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if ((ent->mode & 0222) == 0) {
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pr_debug(" Not writable by anyone\n");
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continue;
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}
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/* Where does data point? */
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addr = (unsigned long)ent->data;
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if (is_module_address(addr))
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where = "module";
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else if (core_kernel_data(addr))
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where = "kernel";
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else
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continue;
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/* If it is writable and points to kernel/module global
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* data, then it's probably a netns leak.
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*/
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WARN(1, "sysctl %s/%s: data points to %s global data: %ps\n",
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path, ent->procname, where, ent->data);
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/* Make it "safe" by dropping writable perms */
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ent->mode &= ~0222;
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}
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}
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struct ctl_table_header *register_net_sysctl(struct net *net,
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const char *path, struct ctl_table *table)
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{
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if (!net_eq(net, &init_net))
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ensure_safe_net_sysctl(net, path, table);
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return __register_sysctl_table(&net->sysctls, path, table);
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}
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EXPORT_SYMBOL_GPL(register_net_sysctl);
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void unregister_net_sysctl_table(struct ctl_table_header *header)
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{
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unregister_sysctl_table(header);
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}
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EXPORT_SYMBOL_GPL(unregister_net_sysctl_table);
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