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>

5 files changed, 145 insertions, 66 deletions

diff --git a/include/linux/netfilter/x_tables.h b/include/linux/netfilter/x_tables.h
index 26ced0c323a5..50c867256ca3 100644
--- a/include/linux/netfilter/x_tables.h
+++ b/include/linux/netfilter/x_tables.h
@@ -401,6 +401,13 @@ struct xt_table_info {
         unsigned int hook_entry[NF_INET_NUMHOOKS];
         unsigned int underflow[NF_INET_NUMHOOKS];
 
+        /*
+         * Number of user chains. Since tables cannot have loops, at most
+         * @stacksize jumps (number of user chains) can possibly be made.
+         */
+        unsigned int stacksize;
+        unsigned int *stackptr;
+        void ***jumpstack;
         /* ipt_entry tables: one per CPU */
         /* Note : this field MUST be the last one, see XT_TABLE_INFO_SZ */
         void *entries[1];
diff --git a/net/ipv4/netfilter/arp_tables.c b/net/ipv4/netfilter/arp_tables.c
index e8e363d90365..07a699059390 100644
--- a/net/ipv4/netfilter/arp_tables.c
+++ b/net/ipv4/netfilter/arp_tables.c
@@ -649,6 +649,9 @@ static int translate_table(struct xt_table_info *newinfo, void *entry0,
                 if (ret != 0)
                         break;
                 ++i;
+                if (strcmp(arpt_get_target(iter)->u.user.name,
+                    XT_ERROR_TARGET) == 0)
+                        ++newinfo->stacksize;
         }
         duprintf("translate_table: ARPT_ENTRY_ITERATE gives %d\n", ret);
         if (ret != 0)
@@ -1774,8 +1777,7 @@ struct xt_table *arpt_register_table(struct net *net,
 {
         int ret;
         struct xt_table_info *newinfo;
-        struct xt_table_info bootstrap
-                = { 0, 0, 0, { 0 }, { 0 }, { } };
+        struct xt_table_info bootstrap = {0};
         void *loc_cpu_entry;
         struct xt_table *new_table;
 
diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.c
index 18c5b1573f3e..70900ecf88e2 100644
--- a/net/ipv4/netfilter/ip_tables.c
+++ b/net/ipv4/netfilter/ip_tables.c
@@ -321,8 +321,6 @@ ipt_do_table(struct sk_buff *skb,
              const struct net_device *out,
              struct xt_table *table)
 {
-#define tb_comefrom ((struct ipt_entry *)table_base)->comefrom
-
         static const char nulldevname[IFNAMSIZ] __attribute__((aligned(sizeof(long))));
         const struct iphdr *ip;
         bool hotdrop = false;
@@ -330,7 +328,8 @@ ipt_do_table(struct sk_buff *skb,
         unsigned int verdict = NF_DROP;
         const char *indev, *outdev;
         const void *table_base;
-        struct ipt_entry *e, *back;
+        struct ipt_entry *e, **jumpstack;
+        unsigned int *stackptr, origptr, cpu;
         const struct xt_table_info *private;
         struct xt_match_param mtpar;
         struct xt_target_param tgpar;
@@ -356,19 +355,23 @@ ipt_do_table(struct sk_buff *skb,
         IP_NF_ASSERT(table->valid_hooks & (1 << hook));
         xt_info_rdlock_bh();
         private = table->private;
-        table_base = private->entries[smp_processor_id()];
+        cpu        = smp_processor_id();
+        table_base = private->entries[cpu];
+        jumpstack  = (struct ipt_entry **)private->jumpstack[cpu];
+        stackptr   = &private->stackptr[cpu];
+        origptr    = *stackptr;
 
         e = get_entry(table_base, private->hook_entry[hook]);
 
-        /* For return from builtin chain */
-        back = get_entry(table_base, private->underflow[hook]);
+        pr_devel("Entering %s(hook %u); sp at %u (UF %p)\n",
+                 table->name, hook, origptr,
+                 get_entry(table_base, private->underflow[hook]));
 
         do {
                 const struct ipt_entry_target *t;
                 const struct xt_entry_match *ematch;
 
                 IP_NF_ASSERT(e);
-                IP_NF_ASSERT(back);
                 if (!ip_packet_match(ip, indev, outdev,
                     &e->ip, mtpar.fragoff)) {
  no_match:
@@ -403,17 +406,28 @@ ipt_do_table(struct sk_buff *skb,
                                         verdict = (unsigned)(-v) - 1;
                                         break;
                                 }
-                                e = back;
-                                back = get_entry(table_base, back->comefrom);
+                                if (*stackptr == 0) {
+                                        e = get_entry(table_base,
+                                            private->underflow[hook]);
+                                        pr_devel("Underflow (this is normal) "
+                                                 "to %p\n", e);
+                                } else {
+                                        e = jumpstack[--*stackptr];
+                                        pr_devel("Pulled %p out from pos %u\n",
+                                                 e, *stackptr);
+                                        e = ipt_next_entry(e);
+                                }
                                 continue;
                         }
                         if (table_base + v != ipt_next_entry(e) &&
                             !(e->ip.flags & IPT_F_GOTO)) {
-                                /* Save old back ptr in next entry */
-                                struct ipt_entry *next = ipt_next_entry(e);
-                                next->comefrom = (void *)back - table_base;
-                                /* set back pointer to next entry */
-                                back = next;
+                                if (*stackptr >= private->stacksize) {
+                                        verdict = NF_DROP;
+                                        break;
+                                }
+                                jumpstack[(*stackptr)++] = e;
+                                pr_devel("Pushed %p into pos %u\n",
+                                         e, *stackptr - 1);
                         }
 
                         e = get_entry(table_base, v);
@@ -426,18 +440,7 @@ ipt_do_table(struct sk_buff *skb,
                 tgpar.targinfo = t->data;
 
 
-#ifdef CONFIG_NETFILTER_DEBUG
-                tb_comefrom = 0xeeeeeeec;
-#endif
                 verdict = t->u.kernel.target->target(skb, &tgpar);
-#ifdef CONFIG_NETFILTER_DEBUG
-                if (tb_comefrom != 0xeeeeeeec && verdict == IPT_CONTINUE) {
-                        printk("Target %s reentered!\n",
-                               t->u.kernel.target->name);
-                        verdict = NF_DROP;
-                }
-                tb_comefrom = 0x57acc001;
-#endif
                 /* Target might have changed stuff. */
                 ip = ip_hdr(skb);
                 if (verdict == IPT_CONTINUE)
@@ -447,7 +450,9 @@ ipt_do_table(struct sk_buff *skb,
                         break;
         } while (!hotdrop);
         xt_info_rdunlock_bh();
-
+        pr_devel("Exiting %s; resetting sp from %u to %u\n",
+                 __func__, *stackptr, origptr);
+        *stackptr = origptr;
 #ifdef DEBUG_ALLOW_ALL
         return NF_ACCEPT;
 #else
@@ -455,8 +460,6 @@ ipt_do_table(struct sk_buff *skb,
                 return NF_DROP;
         else return verdict;
 #endif
-
-#undef tb_comefrom
 }
 
 /* Figures out from what hook each rule can be called: returns 0 if
@@ -838,6 +841,9 @@ translate_table(struct net *net, struct xt_table_info *newinfo, void *entry0,
                 if (ret != 0)
                         return ret;
                 ++i;
+                if (strcmp(ipt_get_target(iter)->u.user.name,
+                    XT_ERROR_TARGET) == 0)
+                        ++newinfo->stacksize;
         }
 
         if (i != repl->num_entries) {
@@ -2086,8 +2092,7 @@ struct xt_table *ipt_register_table(struct net *net,
 {
         int ret;
         struct xt_table_info *newinfo;
-        struct xt_table_info bootstrap
-                = { 0, 0, 0, { 0 }, { 0 }, { } };
+        struct xt_table_info bootstrap = {0};
         void *loc_cpu_entry;
         struct xt_table *new_table;
 
diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_tables.c
index f2b815e72329..2a2770bcd640 100644
--- a/net/ipv6/netfilter/ip6_tables.c
+++ b/net/ipv6/netfilter/ip6_tables.c
@@ -351,15 +351,14 @@ ip6t_do_table(struct sk_buff *skb,
               const struct net_device *out,
               struct xt_table *table)
 {
-#define tb_comefrom ((struct ip6t_entry *)table_base)->comefrom
-
         static const char nulldevname[IFNAMSIZ] __attribute__((aligned(sizeof(long))));
         bool hotdrop = false;
         /* Initializing verdict to NF_DROP keeps gcc happy. */
         unsigned int verdict = NF_DROP;
         const char *indev, *outdev;
         const void *table_base;
-        struct ip6t_entry *e, *back;
+        struct ip6t_entry *e, **jumpstack;
+        unsigned int *stackptr, origptr, cpu;
         const struct xt_table_info *private;
         struct xt_match_param mtpar;
         struct xt_target_param tgpar;
@@ -383,19 +382,19 @@ ip6t_do_table(struct sk_buff *skb,
 
         xt_info_rdlock_bh();
         private = table->private;
-        table_base = private->entries[smp_processor_id()];
+        cpu        = smp_processor_id();
+        table_base = private->entries[cpu];
+        jumpstack  = (struct ip6t_entry **)private->jumpstack[cpu];
+        stackptr   = &private->stackptr[cpu];
+        origptr    = *stackptr;
 
         e = get_entry(table_base, private->hook_entry[hook]);
 
-        /* For return from builtin chain */
-        back = get_entry(table_base, private->underflow[hook]);
-
         do {
                 const struct ip6t_entry_target *t;
                 const struct xt_entry_match *ematch;
 
                 IP_NF_ASSERT(e);
-                IP_NF_ASSERT(back);
                 if (!ip6_packet_match(skb, indev, outdev, &e->ipv6,
                     &mtpar.thoff, &mtpar.fragoff, &hotdrop)) {
  no_match:
@@ -432,17 +431,20 @@ ip6t_do_table(struct sk_buff *skb,
                                         verdict = (unsigned)(-v) - 1;
                                         break;
                                 }
-                                e = back;
-                                back = get_entry(table_base, back->comefrom);
+                                if (*stackptr == 0)
+                                        e = get_entry(table_base,
+                                            private->underflow[hook]);
+                                else
+                                        e = ip6t_next_entry(jumpstack[--*stackptr]);
                                 continue;
                         }
                         if (table_base + v != ip6t_next_entry(e) &&
                             !(e->ipv6.flags & IP6T_F_GOTO)) {
-                                /* Save old back ptr in next entry */
-                                struct ip6t_entry *next = ip6t_next_entry(e);
-                                next->comefrom = (void *)back - table_base;
-                                /* set back pointer to next entry */
-                                back = next;
+                                if (*stackptr >= private->stacksize) {
+                                        verdict = NF_DROP;
+                                        break;
+                                }
+                                jumpstack[(*stackptr)++] = e;
                         }
 
                         e = get_entry(table_base, v);
@@ -454,19 +456,7 @@ ip6t_do_table(struct sk_buff *skb,
                 tgpar.target   = t->u.kernel.target;
                 tgpar.targinfo = t->data;
 
-#ifdef CONFIG_NETFILTER_DEBUG
-                tb_comefrom = 0xeeeeeeec;
-#endif
                 verdict = t->u.kernel.target->target(skb, &tgpar);
-
-#ifdef CONFIG_NETFILTER_DEBUG
-                if (tb_comefrom != 0xeeeeeeec && verdict == IP6T_CONTINUE) {
-                        printk("Target %s reentered!\n",
-                               t->u.kernel.target->name);
-                        verdict = NF_DROP;
-                }
-                tb_comefrom = 0x57acc001;
-#endif
                 if (verdict == IP6T_CONTINUE)
                         e = ip6t_next_entry(e);
                 else
@@ -474,10 +464,8 @@ ip6t_do_table(struct sk_buff *skb,
                         break;
         } while (!hotdrop);
 
-#ifdef CONFIG_NETFILTER_DEBUG
-        tb_comefrom = NETFILTER_LINK_POISON;
-#endif
         xt_info_rdunlock_bh();
+        *stackptr = origptr;
 
 #ifdef DEBUG_ALLOW_ALL
         return NF_ACCEPT;
@@ -486,8 +474,6 @@ ip6t_do_table(struct sk_buff *skb,
                 return NF_DROP;
         else return verdict;
 #endif
-
-#undef tb_comefrom
 }
 
 /* Figures out from what hook each rule can be called: returns 0 if
@@ -869,6 +855,9 @@ translate_table(struct net *net, struct xt_table_info *newinfo, void *entry0,
                 if (ret != 0)
                         return ret;
                 ++i;
+                if (strcmp(ip6t_get_target(iter)->u.user.name,
+                    XT_ERROR_TARGET) == 0)
+                        ++newinfo->stacksize;
         }
 
         if (i != repl->num_entries) {
@@ -2120,8 +2109,7 @@ struct xt_table *ip6t_register_table(struct net *net,
 {
         int ret;
         struct xt_table_info *newinfo;
-        struct xt_table_info bootstrap
-                = { 0, 0, 0, { 0 }, { 0 }, { } };
+        struct xt_table_info bootstrap = {0};
         void *loc_cpu_entry;
         struct xt_table *new_table;
 
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) {