[PATCH 5.11 412/601] inet: use bigger hash table for IP ID generation

Greg Kroah-Hartman
2021-05-12T17:41:55Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit aa6dd211e4b1dde9d5dc25d699d35f789ae7eeba ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/ipv4/route.c | 42 ++++++++++++++++++++++++++++--------------
1 file changed, 28 insertions(+), 14 deletions(-)

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 983b4db1868f..9028205f59f2 100644
--- 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>
@@ -476,8 +477,10 @@ 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;

@@ -487,12 +490,16 @@ 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);

@@ -3547,18 +3554,25 @@ 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);
--
2.30.2