netfilter: x_table: speedup compat operations

One iptables invocation with 135000 rules takes 35 seconds of cpu time
on a recent server, using a 32bit distro and a 64bit kernel.

We eventually trigger NMI/RCU watchdog.

INFO: rcu_sched_state detected stall on CPU 3 (t=6000 jiffies)

COMPAT mode has quadratic behavior and consume 16 bytes of memory per
rule.

Switch the xt_compat algos to use an array instead of list, and use a
binary search to locate an offset in the sorted array.

This halves memory need (8 bytes per rule), and removes quadratic
behavior [ O(N*N) -> O(N*log2(N)) ]

Time of iptables goes from 35 s to 150 ms.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

6 files changed, 57 insertions, 35 deletions

diff --git a/include/linux/netfilter/x_tables.h b/include/linux/netfilter/x_tables.h
index 742bec051440..0f04d985b41c 100644
--- a/include/linux/netfilter/x_tables.h
+++ b/include/linux/netfilter/x_tables.h
@@ -611,8 +611,9 @@ struct _compat_xt_align {
 extern void xt_compat_lock(u_int8_t af);
 extern void xt_compat_unlock(u_int8_t af);
 
-extern int xt_compat_add_offset(u_int8_t af, unsigned int offset, short delta);
+extern int xt_compat_add_offset(u_int8_t af, unsigned int offset, int delta);
 extern void xt_compat_flush_offsets(u_int8_t af);
+extern void xt_compat_init_offsets(u_int8_t af, unsigned int number);
 extern int xt_compat_calc_jump(u_int8_t af, unsigned int offset);
 
 extern int xt_compat_match_offset(const struct xt_match *match);
diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
index 16df0532d4b9..5f1825df9dca 100644
--- a/net/bridge/netfilter/ebtables.c
+++ b/net/bridge/netfilter/ebtables.c
@@ -1764,6 +1764,7 @@ static int compat_table_info(const struct ebt_table_info *info,
 
         newinfo->entries_size = size;
 
+        xt_compat_init_offsets(AF_INET, info->nentries);
         return EBT_ENTRY_ITERATE(entries, size, compat_calc_entry, info,
                                                         entries, newinfo);
 }
diff --git a/net/ipv4/netfilter/arp_tables.c b/net/ipv4/netfilter/arp_tables.c
index 3fac340a28d5..47e5178b998b 100644
--- a/net/ipv4/netfilter/arp_tables.c
+++ b/net/ipv4/netfilter/arp_tables.c
@@ -883,6 +883,7 @@ static int compat_table_info(const struct xt_table_info *info,
         memcpy(newinfo, info, offsetof(struct xt_table_info, entries));
         newinfo->initial_entries = 0;
         loc_cpu_entry = info->entries[raw_smp_processor_id()];
+        xt_compat_init_offsets(NFPROTO_ARP, info->number);
         xt_entry_foreach(iter, loc_cpu_entry, info->size) {
                 ret = compat_calc_entry(iter, info, loc_cpu_entry, newinfo);
                 if (ret != 0)
@@ -1350,6 +1351,7 @@ static int translate_compat_table(const char *name,
         duprintf("translate_compat_table: size %u\n", info->size);
         j = 0;
         xt_compat_lock(NFPROTO_ARP);
+        xt_compat_init_offsets(NFPROTO_ARP, number);
         /* Walk through entries, checking offsets. */
         xt_entry_foreach(iter0, entry0, total_size) {
                 ret = check_compat_entry_size_and_hooks(iter0, info, &size,
diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.c
index a846d633b3b6..c5a75d70970f 100644
--- a/net/ipv4/netfilter/ip_tables.c
+++ b/net/ipv4/netfilter/ip_tables.c
@@ -1080,6 +1080,7 @@ static int compat_table_info(const struct xt_table_info *info,
         memcpy(newinfo, info, offsetof(struct xt_table_info, entries));
         newinfo->initial_entries = 0;
         loc_cpu_entry = info->entries[raw_smp_processor_id()];
+        xt_compat_init_offsets(AF_INET, info->number);
         xt_entry_foreach(iter, loc_cpu_entry, info->size) {
                 ret = compat_calc_entry(iter, info, loc_cpu_entry, newinfo);
                 if (ret != 0)
@@ -1681,6 +1682,7 @@ translate_compat_table(struct net *net,
         duprintf("translate_compat_table: size %u\n", info->size);
         j = 0;
         xt_compat_lock(AF_INET);
+        xt_compat_init_offsets(AF_INET, number);
         /* Walk through entries, checking offsets. */
         xt_entry_foreach(iter0, entry0, total_size) {
                 ret = check_compat_entry_size_and_hooks(iter0, info, &size,
diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_tables.c
index 455582384ece..0c9973a657fb 100644
--- a/net/ipv6/netfilter/ip6_tables.c
+++ b/net/ipv6/netfilter/ip6_tables.c
@@ -1093,6 +1093,7 @@ static int compat_table_info(const struct xt_table_info *info,
         memcpy(newinfo, info, offsetof(struct xt_table_info, entries));
         newinfo->initial_entries = 0;
         loc_cpu_entry = info->entries[raw_smp_processor_id()];
+        xt_compat_init_offsets(AF_INET6, info->number);
         xt_entry_foreach(iter, loc_cpu_entry, info->size) {
                 ret = compat_calc_entry(iter, info, loc_cpu_entry, newinfo);
                 if (ret != 0)
@@ -1696,6 +1697,7 @@ translate_compat_table(struct net *net,
         duprintf("translate_compat_table: size %u\n", info->size);
         j = 0;
         xt_compat_lock(AF_INET6);
+        xt_compat_init_offsets(AF_INET6, number);
         /* Walk through entries, checking offsets. */
         xt_entry_foreach(iter0, entry0, total_size) {
                 ret = check_compat_entry_size_and_hooks(iter0, info, &size,
diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
index 80463507420e..ee5de3af510a 100644
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -38,9 +38,8 @@ MODULE_DESCRIPTION("{ip,ip6,arp,eb}_tables backend module");
 #define SMP_ALIGN(x) (((x) + SMP_CACHE_BYTES-1) & ~(SMP_CACHE_BYTES-1))
 
 struct compat_delta {
-        struct compat_delta *next;
-        unsigned int offset;
-        int delta;
+        unsigned int offset; /* offset in kernel */
+        int delta; /* delta in 32bit user land */
 };
 
 struct xt_af {
@@ -49,7 +48,9 @@ struct xt_af {
         struct list_head target;
 #ifdef CONFIG_COMPAT
         struct mutex compat_mutex;
-        struct compat_delta *compat_offsets;
+        struct compat_delta *compat_tab;
+        unsigned int number; /* number of slots in compat_tab[] */
+        unsigned int cur; /* number of used slots in compat_tab[] */
 #endif
 };
 
@@ -414,54 +415,67 @@ int xt_check_match(struct xt_mtchk_param *par,
 EXPORT_SYMBOL_GPL(xt_check_match);
 
 #ifdef CONFIG_COMPAT
-int xt_compat_add_offset(u_int8_t af, unsigned int offset, short delta)
+int xt_compat_add_offset(u_int8_t af, unsigned int offset, int delta)
 {
-        struct compat_delta *tmp;
+        struct xt_af *xp = &xt[af];
 
-        tmp = kmalloc(sizeof(struct compat_delta), GFP_KERNEL);
-        if (!tmp)
-                return -ENOMEM;
+        if (!xp->compat_tab) {
+                if (!xp->number)
+                        return -EINVAL;
+                xp->compat_tab = vmalloc(sizeof(struct compat_delta) * xp->number);
+                if (!xp->compat_tab)
+                        return -ENOMEM;
+                xp->cur = 0;
+        }
 
-        tmp->offset = offset;
-        tmp->delta = delta;
+        if (xp->cur >= xp->number)
+                return -EINVAL;
 
-        if (xt[af].compat_offsets) {
-                tmp->next = xt[af].compat_offsets->next;
-                xt[af].compat_offsets->next = tmp;
-        } else {
-                xt[af].compat_offsets = tmp;
-                tmp->next = NULL;
-        }
+        if (xp->cur)
+                delta += xp->compat_tab[xp->cur - 1].delta;
+        xp->compat_tab[xp->cur].offset = offset;
+        xp->compat_tab[xp->cur].delta = delta;
+        xp->cur++;
         return 0;
 }
 EXPORT_SYMBOL_GPL(xt_compat_add_offset);
 
 void xt_compat_flush_offsets(u_int8_t af)
 {
-        struct compat_delta *tmp, *next;
-
-        if (xt[af].compat_offsets) {
-                for (tmp = xt[af].compat_offsets; tmp; tmp = next) {
-                        next = tmp->next;
-                        kfree(tmp);
-                }
-                xt[af].compat_offsets = NULL;
+        if (xt[af].compat_tab) {
+                vfree(xt[af].compat_tab);
+                xt[af].compat_tab = NULL;
+                xt[af].number = 0;
         }
 }
 EXPORT_SYMBOL_GPL(xt_compat_flush_offsets);
 
 int xt_compat_calc_jump(u_int8_t af, unsigned int offset)
 {
-        struct compat_delta *tmp;
-        int delta;
-
-        for (tmp = xt[af].compat_offsets, delta = 0; tmp; tmp = tmp->next)
-                if (tmp->offset < offset)
-                        delta += tmp->delta;
-        return delta;
+        struct compat_delta *tmp = xt[af].compat_tab;
+        int mid, left = 0, right = xt[af].cur - 1;
+
+        while (left <= right) {
+                mid = (left + right) >> 1;
+                if (offset > tmp[mid].offset)
+                        left = mid + 1;
+                else if (offset < tmp[mid].offset)
+                        right = mid - 1;
+                else
+                        return mid ? tmp[mid - 1].delta : 0;
+        }
+        WARN_ON_ONCE(1);
+        return 0;
 }
 EXPORT_SYMBOL_GPL(xt_compat_calc_jump);
 
+void xt_compat_init_offsets(u_int8_t af, unsigned int number)
+{
+        xt[af].number = number;
+        xt[af].cur = 0;
+}
+EXPORT_SYMBOL(xt_compat_init_offsets);
+
 int xt_compat_match_offset(const struct xt_match *match)
 {
         u_int16_t csize = match->compatsize ? : match->matchsize;
@@ -1337,7 +1351,7 @@ static int __init xt_init(void)
                 mutex_init(&xt[i].mutex);
 #ifdef CONFIG_COMPAT
                 mutex_init(&xt[i].compat_mutex);
-                xt[i].compat_offsets = NULL;
+                xt[i].compat_tab = NULL;
 #endif
                 INIT_LIST_HEAD(&xt[i].target);
                 INIT_LIST_HEAD(&xt[i].match);