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inet: use bigger hash table for IP ID generation

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In commit 73f156a6e8 ("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: 73f156a6e8 ("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>
This commit is contained in:
Eric Dumazet 2021-03-24 14:53:37 -07:00 committed by David S. Miller
parent eb9da2c1b6
commit aa6dd211e4
1 changed files with 28 additions and 14 deletions
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42
net/ipv4/route.c
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@ -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);
prandom_bytes(ip_idents, IP_IDENTS_SZ * sizeof(*ip_idents));
ip_idents = idents_hash;
ip_tstamps = kcalloc(IP_IDENTS_SZ, sizeof(*ip_tstamps), GFP_KERNEL);
if (!ip_tstamps)
panic("IP: failed to allocate ip_tstamps\n");
prandom_bytes(ip_idents, (ip_idents_mask + 1) * sizeof(*ip_idents));
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);