@@ -115,9 +115,57 @@ __init int net_sysctl_init(void)
goto out;
}
+/* Verify that sysctls for non-init netns are safe by either:
+ * 1) being read-only, or
+ * 2) having a data pointer which points outside of the global kernel/module
+ * data segment, and rather into the heap where a per-net object was
+ * allocated.
+ */
+static void ensure_safe_net_sysctl(struct net *net, const char *path,
+ struct ctl_table *table)
+{
+ struct ctl_table *ent;
+
+ pr_debug("Registering net sysctl (net %p): %s\n", net, path);
+ for (ent = table; ent->procname; ent++) {
+ unsigned long addr;
+ const char *where;
+
+ pr_debug(" procname=%s mode=%o proc_handler=%ps data=%p\n",
+ ent->procname, ent->mode, ent->proc_handler, ent->data);
+
+ /* If it's not writable inside the netns, then it can't hurt. */
+ if ((ent->mode & 0222) == 0) {
+ pr_debug(" Not writable by anyone\n");
+ continue;
+ }
+
+ /* Where does data point? */
+ addr = (unsigned long)ent->data;
+ if (is_module_address(addr))
+ where = "module";
+ else if (core_kernel_data(addr))
+ where = "kernel";
+ else
+ continue;
+
+ /* If it is writable and points to kernel/module global
+ * data, then it's probably a netns leak.
+ */
+ WARN(1, "sysctl %s/%s: data points to %s global data: %ps\n",
+ path, ent->procname, where, ent->data);
+
+ /* Make it "safe" by dropping writable perms */
+ ent->mode &= ~0222;
+ }
+}
+
struct ctl_table_header *register_net_sysctl(struct net *net,
const char *path, struct ctl_table *table)
{
+ if (!net_eq(net, &init_net))
+ ensure_safe_net_sysctl(net, path, table);
+
return __register_sysctl_table(&net->sysctls, path, table);
}
EXPORT_SYMBOL_GPL(register_net_sysctl);
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> --- net/sysctl_net.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 48 insertions(+)