Subject: inet: use bigger hash table for IP ID generation (backported to 4.19)
From: Amit Klein <[email protected]>
This is a backport to 4.19 of the following patch, originally
developed by Eric Dumazet.
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 <[email protected]>
Cc: [email protected]
Cc: Eric Dumazet <[email protected]>
Cc: Willy Tarreau <[email protected]>
---
net/ipv4/route.c | 42 ++++++++++++++++++++++++++++--------------
1 file changed, 28 insertions(+), 14 deletions(-)
(limited to 'net/ipv4/route.c')
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 0470442ff61d6..ea916df1bbf5e 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/bootmem.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);
--
cgit 1.2.3-1.el7
On Thu, Jun 17, 2021 at 01:19:18AM -0700, Amit Klein wrote:
> Subject: inet: use bigger hash table for IP ID generation (backported to 4.19)
> From: Amit Klein <[email protected]>
>
> This is a backport to 4.19 of the following patch, originally
> developed by Eric Dumazet.
>
> 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 <[email protected]>
> Cc: [email protected]
> Cc: Eric Dumazet <[email protected]>
> Cc: Willy Tarreau <[email protected]>
> ---
> net/ipv4/route.c | 42 ++++++++++++++++++++++++++++--------------
> 1 file changed, 28 insertions(+), 14 deletions(-)
>
> (limited to 'net/ipv4/route.c')
I had to dig up what the upstream git commit id was for this, please
specify it next time :(
I've queued this, and the 4.14 version up. Can you create a 4.4.y and
4.9.y version as well?
thanks,
greg k-h
On Mon, Jun 21, 2021 at 6:28 PM Greg KH <[email protected]> wrote:
>
> On Thu, Jun 17, 2021 at 01:19:18AM -0700, Amit Klein wrote:
> > Subject: inet: use bigger hash table for IP ID generation (backported to 4.19)
> > From: Amit Klein <[email protected]>
[...]
>
> I had to dig up what the upstream git commit id was for this, please
> specify it next time :(
>
Sure. Awfully sorry about the omission.
> I've queued this, and the 4.14 version up.
Thanks.
Can you create a 4.4.y and
> 4.9.y version as well?
>
Absolutely. I plan to do so later this week.
-Amit
On Mon, Jun 21, 2021 at 6:28 PM Greg KH <[email protected]> wrote:
>
> On Thu, Jun 17, 2021 at 01:19:18AM -0700, Amit Klein wrote:
> > Subject: inet: use bigger hash table for IP ID generation (backported to 4.19)
> > From: Amit Klein <[email protected]>
[...]
>
> I've queued this, and the 4.14 version up. Can you create a 4.4.y and
> 4.9.y version as well?
>
Done and submitted (a few minutes ago). Note the subject line has
"[PATCH 4.9]" but it also fixes 4.4 (I didn't know what convention to
use for this case).
Best,
-Amit