This is a note to let you know that I've just added the patch titled inet: use bigger hash table for IP ID generation to the 4.19-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: inet-use-bigger-hash-table-for-ip-id-generation.patch and it can be found in the queue-4.19 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From aa6dd211e4b1dde9d5dc25d699d35f789ae7eeba Mon Sep 17 00:00:00 2001 From: Eric Dumazet <edumazet@xxxxxxxxxx> Date: Wed, 24 Mar 2021 14:53:37 -0700 Subject: inet: use bigger hash table for IP ID generation From: Eric Dumazet <edumazet@xxxxxxxxxx> commit aa6dd211e4b1dde9d5dc25d699d35f789ae7eeba upstream. 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@xxxxxxxxx> Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx> Cc: Willy Tarreau <w@xxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/ipv4/route.c | 46 ++++++++++++++++++++++++++++++---------------- 1 file changed, 30 insertions(+), 16 deletions(-) --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -70,6 +70,7 @@ #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> @@ -470,8 +471,10 @@ static void ipv4_confirm_neigh(const str __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; @@ -481,12 +484,16 @@ 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); @@ -3197,18 +3204,25 @@ struct ip_rt_acct __percpu *ip_rt_acct _ 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"); - - prandom_bytes(ip_idents, IP_IDENTS_SZ * 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"); + /* 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_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); Patches currently in stable-queue which might be from edumazet@xxxxxxxxxx are queue-4.19/net-af_unix-fix-a-data-race-in-unix_dgram_sendmsg-un.patch queue-4.19/inet-use-bigger-hash-table-for-ip-id-generation.patch