netfilter: xtables: make ip_tables reentrant

Currently, the table traverser stores return addresses in the ruleset
itself (struct ip6t_entry->comefrom). This has a well-known drawback:
the jumpstack is overwritten on reentry, making it necessary for
targets to return absolute verdicts. Also, the ruleset (which might
be heavy memory-wise) needs to be replicated for each CPU that can
possibly invoke ip6t_do_table.

This patch decouples the jumpstack from struct ip6t_entry and instead
puts it into xt_table_info. Not being restricted by 'comefrom'
anymore, we can set up a stack as needed. By default, there is room
allocated for two entries into the traverser.

arp_tables is not touched though, because there is just one/two
modules and further patches seek to collapse the table traverser
anyhow.

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
Signed-off-by: Patrick McHardy <kaber@trash.net>

1 files changed, 77 insertions, 0 deletions

diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
index 8e23d8f68459..edde5c602890 100644
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -62,6 +62,9 @@ static const char *const xt_prefix[NFPROTO_NUMPROTO] = {
         [NFPROTO_IPV6]   = "ip6",
 };
 
+/* Allow this many total (re)entries. */
+static const unsigned int xt_jumpstack_multiplier = 2;
+
 /* Registration hooks for targets. */
 int
 xt_register_target(struct xt_target *target)
@@ -680,6 +683,26 @@ void xt_free_table_info(struct xt_table_info *info)
                 else
                         vfree(info->entries[cpu]);
         }
+
+        if (info->jumpstack != NULL) {
+                if (sizeof(void *) * info->stacksize > PAGE_SIZE) {
+                        for_each_possible_cpu(cpu)
+                                vfree(info->jumpstack[cpu]);
+                } else {
+                        for_each_possible_cpu(cpu)
+                                kfree(info->jumpstack[cpu]);
+                }
+        }
+
+        if (sizeof(void **) * nr_cpu_ids > PAGE_SIZE)
+                vfree(info->jumpstack);
+        else
+                kfree(info->jumpstack);
+        if (sizeof(unsigned int) * nr_cpu_ids > PAGE_SIZE)
+                vfree(info->stackptr);
+        else
+                kfree(info->stackptr);
+
         kfree(info);
 }
 EXPORT_SYMBOL(xt_free_table_info);
@@ -724,6 +747,49 @@ EXPORT_SYMBOL_GPL(xt_compat_unlock);
 DEFINE_PER_CPU(struct xt_info_lock, xt_info_locks);
 EXPORT_PER_CPU_SYMBOL_GPL(xt_info_locks);
 
+static int xt_jumpstack_alloc(struct xt_table_info *i)
+{
+        unsigned int size;
+        int cpu;
+
+        size = sizeof(unsigned int) * nr_cpu_ids;
+        if (size > PAGE_SIZE)
+                i->stackptr = vmalloc(size);
+        else
+                i->stackptr = kmalloc(size, GFP_KERNEL);
+        if (i->stackptr == NULL)
+                return -ENOMEM;
+        memset(i->stackptr, 0, size);
+
+        size = sizeof(void **) * nr_cpu_ids;
+        if (size > PAGE_SIZE)
+                i->jumpstack = vmalloc(size);
+        else
+                i->jumpstack = kmalloc(size, GFP_KERNEL);
+        if (i->jumpstack == NULL)
+                return -ENOMEM;
+        memset(i->jumpstack, 0, size);
+
+        i->stacksize *= xt_jumpstack_multiplier;
+        size = sizeof(void *) * i->stacksize;
+        for_each_possible_cpu(cpu) {
+                if (size > PAGE_SIZE)
+                        i->jumpstack[cpu] = vmalloc_node(size,
+                                cpu_to_node(cpu));
+                else
+                        i->jumpstack[cpu] = kmalloc_node(size,
+                                GFP_KERNEL, cpu_to_node(cpu));
+                if (i->jumpstack[cpu] == NULL)
+                        /*
+                         * Freeing will be done later on by the callers. The
+                         * chain is: xt_replace_table -> __do_replace ->
+                         * do_replace -> xt_free_table_info.
+                         */
+                        return -ENOMEM;
+        }
+
+        return 0;
+}
 
 struct xt_table_info *
 xt_replace_table(struct xt_table *table,
@@ -732,6 +798,7 @@ xt_replace_table(struct xt_table *table,
               int *error)
 {
         struct xt_table_info *private;
+        int ret;
 
         /* Do the substitution. */
         local_bh_disable();
@@ -746,6 +813,12 @@ xt_replace_table(struct xt_table *table,
                 return NULL;
         }
 
+        ret = xt_jumpstack_alloc(newinfo);
+        if (ret < 0) {
+                *error = ret;
+                return NULL;
+        }
+
         table->private = newinfo;
         newinfo->initial_entries = private->initial_entries;
 
@@ -770,6 +843,10 @@ struct xt_table *xt_register_table(struct net *net,
         struct xt_table_info *private;
         struct xt_table *t, *table;
 
+        ret = xt_jumpstack_alloc(newinfo);
+        if (ret < 0)
+                return ERR_PTR(ret);
+
         /* Don't add one object to multiple lists. */
         table = kmemdup(input_table, sizeof(struct xt_table), GFP_KERNEL);
         if (!table) {