inet: use bigger hash table for IP ID generation

In commit 73f156a6e8c1 ("inetpeer: get rid of ip_id_count")
I used a very small hash table that could be abused
by patient attackers to reveal sensitive information.

Switch to a dynamic sizing, depending on RAM size.

Typical big hosts will now use 128x more storage (2 MB)
to get a similar increase in security and reduction
of hash collisions.

As a bonus, use of alloc_large_system_hash() spreads
allocated memory among all NUMA nodes.

Fixes: 73f156a6e8c1 ("inetpeer: get rid of ip_id_count")
Reported-by: Amit Klein <aksecurity@gmail.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willy Tarreau <w@1wt.eu>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 0470442..ea916df 100644 (file)
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -66,6 +66,7 @@
 #include <linux/types.h>
 #include <linux/kernel.h>
 #include <linux/mm.h>
+#include <linux/memblock.h>
 #include <linux/string.h>
 #include <linux/socket.h>
 #include <linux/sockios.h>
@@ -452,8 +453,10 @@ static void ipv4_confirm_neigh(const struct dst_entry *dst, const void *daddr)
        __ipv4_confirm_neigh(dev, *(__force u32 *)pkey);
 }
 
-#define IP_IDENTS_SZ 2048u
-
+/* Hash tables of size 2048..262144 depending on RAM size.
+ * Each bucket uses 8 bytes.
+ */
+static u32 ip_idents_mask __read_mostly;
 static atomic_t *ip_idents __read_mostly;
 static u32 *ip_tstamps __read_mostly;
 
@@ -463,12 +466,16 @@ static u32 *ip_tstamps __read_mostly;
  */
 u32 ip_idents_reserve(u32 hash, int segs)
 {
-       u32 *p_tstamp = ip_tstamps + hash % IP_IDENTS_SZ;
-       atomic_t *p_id = ip_idents + hash % IP_IDENTS_SZ;
-       u32 old = READ_ONCE(*p_tstamp);
-       u32 now = (u32)jiffies;
+       u32 bucket, old, now = (u32)jiffies;
+       atomic_t *p_id;
+       u32 *p_tstamp;
        u32 delta = 0;
 
+       bucket = hash & ip_idents_mask;
+       p_tstamp = ip_tstamps + bucket;
+       p_id = ip_idents + bucket;
+       old = READ_ONCE(*p_tstamp);
+
        if (old != now && cmpxchg(p_tstamp, old, now) == old)
                delta = prandom_u32_max(now - old);
 
@@ -3557,18 +3564,25 @@ struct ip_rt_acct __percpu *ip_rt_acct __read_mostly;
 
 int __init ip_rt_init(void)
 {
+       void *idents_hash;
        int cpu;
 
-       ip_idents = kmalloc_array(IP_IDENTS_SZ, sizeof(*ip_idents),
-                                 GFP_KERNEL);
-       if (!ip_idents)
-               panic("IP: failed to allocate ip_idents\n");
+       /* For modern hosts, this will use 2 MB of memory */
+       idents_hash = alloc_large_system_hash("IP idents",
+                                             sizeof(*ip_idents) + sizeof(*ip_tstamps),
+                                             0,
+                                             16, /* one bucket per 64 KB */
+                                             HASH_ZERO,
+                                             NULL,
+                                             &ip_idents_mask,
+                                             2048,
+                                             256*1024);
+
+       ip_idents = idents_hash;
 
-       prandom_bytes(ip_idents, IP_IDENTS_SZ * sizeof(*ip_idents));
+       prandom_bytes(ip_idents, (ip_idents_mask + 1) * sizeof(*ip_idents));
 
-       ip_tstamps = kcalloc(IP_IDENTS_SZ, sizeof(*ip_tstamps), GFP_KERNEL);
-       if (!ip_tstamps)
-               panic("IP: failed to allocate ip_tstamps\n");
+       ip_tstamps = idents_hash + (ip_idents_mask + 1) * sizeof(*ip_idents);
 
        for_each_possible_cpu(cpu) {
                struct uncached_list *ul = &per_cpu(rt_uncached_list, cpu);