[PATCH 5.3 133/140] net/flow_dissector: switch to siphash

From: Greg Kroah-Hartman
Date: Fri Nov 08 2019 - 14:10:36 EST

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From: Eric Dumazet <edumazet@xxxxxxxxxx>

commit 55667441c84fa5e0911a0aac44fb059c15ba6da2 upstream.

UDP IPv6 packets auto flowlabels are using a 32bit secret
(static u32 hashrnd in net/core/flow_dissector.c) and
apply jhash() over fields known by the receivers.

Attackers can easily infer the 32bit secret and use this information
to identify a device and/or user, since this 32bit secret is only
set at boot time.

Really, using jhash() to generate cookies sent on the wire
is a serious security concern.

Trying to change the rol32(hash, 16) in ip6_make_flowlabel() would be
a dead end. Trying to periodically change the secret (like in sch_sfq.c)
could change paths taken in the network for long lived flows.

Let's switch to siphash, as we did in commit df453700e8d8
("inet: switch IP ID generator to siphash")

Using a cryptographically strong pseudo random function will solve this
privacy issue and more generally remove other weak points in the stack.

Packet schedulers using skb_get_hash_perturb() benefit from this change.

Fixes: b56774163f99 ("ipv6: Enable auto flow labels by default")
Fixes: 42240901f7c4 ("ipv6: Implement different admin modes for automatic flow labels")
Fixes: 67800f9b1f4e ("ipv6: Call skb_get_hash_flowi6 to get skb->hash in ip6_make_flowlabel")
Fixes: cb1ce2ef387b ("ipv6: Implement automatic flow label generation on transmit")
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Reported-by: Jonathan Berger <jonathann1@xxxxxxxxx>
Reported-by: Amit Klein <aksecurity@xxxxxxxxx>
Reported-by: Benny Pinkas <benny@xxxxxxxxxx>
Cc: Tom Herbert <tom@xxxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
include/linux/skbuff.h | 3 ++-
include/net/flow_dissector.h | 3 ++-
include/net/fq.h | 2 +-
include/net/fq_impl.h | 4 ++--
net/core/flow_dissector.c | 38 ++++++++++++++++----------------------
net/sched/sch_hhf.c | 8 ++++----
net/sched/sch_sfb.c | 13 +++++++------
net/sched/sch_sfq.c | 14 ++++++++------
8 files changed, 42 insertions(+), 43 deletions(-)

--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1360,7 +1360,8 @@ static inline __u32 skb_get_hash_flowi6(
return skb->hash;
}

-__u32 skb_get_hash_perturb(const struct sk_buff *skb, u32 perturb);
+__u32 skb_get_hash_perturb(const struct sk_buff *skb,
+ const siphash_key_t *perturb);

static inline __u32 skb_get_hash_raw(const struct sk_buff *skb)
{
--- a/include/net/flow_dissector.h
+++ b/include/net/flow_dissector.h
@@ -4,6 +4,7 @@

#include <linux/types.h>
#include <linux/in6.h>
+#include <linux/siphash.h>
#include <uapi/linux/if_ether.h>

/**
@@ -276,7 +277,7 @@ struct flow_keys_basic {
struct flow_keys {
struct flow_dissector_key_control control;
#define FLOW_KEYS_HASH_START_FIELD basic
- struct flow_dissector_key_basic basic;
+ struct flow_dissector_key_basic basic __aligned(SIPHASH_ALIGNMENT);
struct flow_dissector_key_tags tags;
struct flow_dissector_key_vlan vlan;
struct flow_dissector_key_vlan cvlan;
--- a/include/net/fq.h
+++ b/include/net/fq.h
@@ -69,7 +69,7 @@ struct fq {
struct list_head backlogs;
spinlock_t lock;
u32 flows_cnt;
- u32 perturbation;
+ siphash_key_t perturbation;
u32 limit;
u32 memory_limit;
u32 memory_usage;
--- a/include/net/fq_impl.h
+++ b/include/net/fq_impl.h
@@ -108,7 +108,7 @@ begin:

static u32 fq_flow_idx(struct fq *fq, struct sk_buff *skb)
{
- u32 hash = skb_get_hash_perturb(skb, fq->perturbation);
+ u32 hash = skb_get_hash_perturb(skb, &fq->perturbation);

return reciprocal_scale(hash, fq->flows_cnt);
}
@@ -308,7 +308,7 @@ static int fq_init(struct fq *fq, int fl
INIT_LIST_HEAD(&fq->backlogs);
spin_lock_init(&fq->lock);
fq->flows_cnt = max_t(u32, flows_cnt, 1);
- fq->perturbation = prandom_u32();
+ get_random_bytes(&fq->perturbation, sizeof(fq->perturbation));
fq->quantum = 300;
fq->limit = 8192;
fq->memory_limit = 16 << 20; /* 16 MBytes */
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -1333,30 +1333,21 @@ out_bad:
}
EXPORT_SYMBOL(__skb_flow_dissect);

-static u32 hashrnd __read_mostly;
+static siphash_key_t hashrnd __read_mostly;
static __always_inline void __flow_hash_secret_init(void)
{
net_get_random_once(&hashrnd, sizeof(hashrnd));
}

-static __always_inline u32 __flow_hash_words(const u32 *words, u32 length,
- u32 keyval)
+static const void *flow_keys_hash_start(const struct flow_keys *flow)
{
- return jhash2(words, length, keyval);
-}
-
-static inline const u32 *flow_keys_hash_start(const struct flow_keys *flow)
-{
- const void *p = flow;
-
- BUILD_BUG_ON(FLOW_KEYS_HASH_OFFSET % sizeof(u32));
- return (const u32 *)(p + FLOW_KEYS_HASH_OFFSET);
+ BUILD_BUG_ON(FLOW_KEYS_HASH_OFFSET % SIPHASH_ALIGNMENT);
+ return &flow->FLOW_KEYS_HASH_START_FIELD;
}

static inline size_t flow_keys_hash_length(const struct flow_keys *flow)
{
size_t diff = FLOW_KEYS_HASH_OFFSET + sizeof(flow->addrs);
- BUILD_BUG_ON((sizeof(*flow) - FLOW_KEYS_HASH_OFFSET) % sizeof(u32));
BUILD_BUG_ON(offsetof(typeof(*flow), addrs) !=
sizeof(*flow) - sizeof(flow->addrs));

@@ -1371,7 +1362,7 @@ static inline size_t flow_keys_hash_leng
diff -= sizeof(flow->addrs.tipckey);
break;
}
- return (sizeof(*flow) - diff) / sizeof(u32);
+ return sizeof(*flow) - diff;
}

__be32 flow_get_u32_src(const struct flow_keys *flow)
@@ -1437,14 +1428,15 @@ static inline void __flow_hash_consisten
}
}

-static inline u32 __flow_hash_from_keys(struct flow_keys *keys, u32 keyval)
+static inline u32 __flow_hash_from_keys(struct flow_keys *keys,
+ const siphash_key_t *keyval)
{
u32 hash;

__flow_hash_consistentify(keys);

- hash = __flow_hash_words(flow_keys_hash_start(keys),
- flow_keys_hash_length(keys), keyval);
+ hash = siphash(flow_keys_hash_start(keys),
+ flow_keys_hash_length(keys), keyval);
if (!hash)
hash = 1;

@@ -1454,12 +1446,13 @@ static inline u32 __flow_hash_from_keys(
u32 flow_hash_from_keys(struct flow_keys *keys)
{
__flow_hash_secret_init();
- return __flow_hash_from_keys(keys, hashrnd);
+ return __flow_hash_from_keys(keys, &hashrnd);
}
EXPORT_SYMBOL(flow_hash_from_keys);

static inline u32 ___skb_get_hash(const struct sk_buff *skb,
- struct flow_keys *keys, u32 keyval)
+ struct flow_keys *keys,
+ const siphash_key_t *keyval)
{
skb_flow_dissect_flow_keys(skb, keys,
FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL);
@@ -1507,7 +1500,7 @@ u32 __skb_get_hash_symmetric(const struc
&keys, NULL, 0, 0, 0,
FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL);

- return __flow_hash_from_keys(&keys, hashrnd);
+ return __flow_hash_from_keys(&keys, &hashrnd);
}
EXPORT_SYMBOL_GPL(__skb_get_hash_symmetric);

@@ -1527,13 +1520,14 @@ void __skb_get_hash(struct sk_buff *skb)

__flow_hash_secret_init();

- hash = ___skb_get_hash(skb, &keys, hashrnd);
+ hash = ___skb_get_hash(skb, &keys, &hashrnd);

__skb_set_sw_hash(skb, hash, flow_keys_have_l4(&keys));
}
EXPORT_SYMBOL(__skb_get_hash);

-__u32 skb_get_hash_perturb(const struct sk_buff *skb, u32 perturb)
+__u32 skb_get_hash_perturb(const struct sk_buff *skb,
+ const siphash_key_t *perturb)
{
struct flow_keys keys;

--- a/net/sched/sch_hhf.c
+++ b/net/sched/sch_hhf.c
@@ -5,11 +5,11 @@
* Copyright (C) 2013 Nandita Dukkipati <nanditad@xxxxxxxxxx>
*/

-#include <linux/jhash.h>
#include <linux/jiffies.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/vmalloc.h>
+#include <linux/siphash.h>
#include <net/pkt_sched.h>
#include <net/sock.h>

@@ -126,7 +126,7 @@ struct wdrr_bucket {

struct hhf_sched_data {
struct wdrr_bucket buckets[WDRR_BUCKET_CNT];
- u32 perturbation; /* hash perturbation */
+ siphash_key_t perturbation; /* hash perturbation */
u32 quantum; /* psched_mtu(qdisc_dev(sch)); */
u32 drop_overlimit; /* number of times max qdisc packet
* limit was hit
@@ -264,7 +264,7 @@ static enum wdrr_bucket_idx hhf_classify
}

/* Get hashed flow-id of the skb. */
- hash = skb_get_hash_perturb(skb, q->perturbation);
+ hash = skb_get_hash_perturb(skb, &q->perturbation);

/* Check if this packet belongs to an already established HH flow. */
flow_pos = hash & HHF_BIT_MASK;
@@ -582,7 +582,7 @@ static int hhf_init(struct Qdisc *sch, s

sch->limit = 1000;
q->quantum = psched_mtu(qdisc_dev(sch));
- q->perturbation = prandom_u32();
+ get_random_bytes(&q->perturbation, sizeof(q->perturbation));
INIT_LIST_HEAD(&q->new_buckets);
INIT_LIST_HEAD(&q->old_buckets);

--- a/net/sched/sch_sfb.c
+++ b/net/sched/sch_sfb.c
@@ -18,7 +18,7 @@
#include <linux/errno.h>
#include <linux/skbuff.h>
#include <linux/random.h>
-#include <linux/jhash.h>
+#include <linux/siphash.h>
#include <net/ip.h>
#include <net/pkt_sched.h>
#include <net/pkt_cls.h>
@@ -45,7 +45,7 @@ struct sfb_bucket {
* (Section 4.4 of SFB reference : moving hash functions)
*/
struct sfb_bins {
- u32 perturbation; /* jhash perturbation */
+ siphash_key_t perturbation; /* siphash key */
struct sfb_bucket bins[SFB_LEVELS][SFB_NUMBUCKETS];
};

@@ -217,7 +217,8 @@ static u32 sfb_compute_qlen(u32 *prob_r,

static void sfb_init_perturbation(u32 slot, struct sfb_sched_data *q)
{
- q->bins[slot].perturbation = prandom_u32();
+ get_random_bytes(&q->bins[slot].perturbation,
+ sizeof(q->bins[slot].perturbation));
}

static void sfb_swap_slot(struct sfb_sched_data *q)
@@ -314,9 +315,9 @@ static int sfb_enqueue(struct sk_buff *s
/* If using external classifiers, get result and record it. */
if (!sfb_classify(skb, fl, &ret, &salt))
goto other_drop;
- sfbhash = jhash_1word(salt, q->bins[slot].perturbation);
+ sfbhash = siphash_1u32(salt, &q->bins[slot].perturbation);
} else {
- sfbhash = skb_get_hash_perturb(skb, q->bins[slot].perturbation);
+ sfbhash = skb_get_hash_perturb(skb, &q->bins[slot].perturbation);
}

@@ -352,7 +353,7 @@ static int sfb_enqueue(struct sk_buff *s
/* Inelastic flow */
if (q->double_buffering) {
sfbhash = skb_get_hash_perturb(skb,
- q->bins[slot].perturbation);
+ &q->bins[slot].perturbation);
if (!sfbhash)
sfbhash = 1;
sfb_skb_cb(skb)->hashes[slot] = sfbhash;
--- a/net/sched/sch_sfq.c
+++ b/net/sched/sch_sfq.c
@@ -14,7 +14,7 @@
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/skbuff.h>
-#include <linux/jhash.h>
+#include <linux/siphash.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <net/netlink.h>
@@ -117,7 +117,7 @@ struct sfq_sched_data {
u8 headdrop;
u8 maxdepth; /* limit of packets per flow */

- u32 perturbation;
+ siphash_key_t perturbation;
u8 cur_depth; /* depth of longest slot */
u8 flags;
unsigned short scaled_quantum; /* SFQ_ALLOT_SIZE(quantum) */
@@ -157,7 +157,7 @@ static inline struct sfq_head *sfq_dep_h
static unsigned int sfq_hash(const struct sfq_sched_data *q,
const struct sk_buff *skb)
{
- return skb_get_hash_perturb(skb, q->perturbation) & (q->divisor - 1);
+ return skb_get_hash_perturb(skb, &q->perturbation) & (q->divisor - 1);
}

static unsigned int sfq_classify(struct sk_buff *skb, struct Qdisc *sch,
@@ -607,9 +607,11 @@ static void sfq_perturbation(struct time
struct sfq_sched_data *q = from_timer(q, t, perturb_timer);
struct Qdisc *sch = q->sch;
spinlock_t *root_lock = qdisc_lock(qdisc_root_sleeping(sch));
+ siphash_key_t nkey;

+ get_random_bytes(&nkey, sizeof(nkey));
spin_lock(root_lock);
- q->perturbation = prandom_u32();
+ q->perturbation = nkey;
if (!q->filter_list && q->tail)
sfq_rehash(sch);
spin_unlock(root_lock);
@@ -688,7 +690,7 @@ static int sfq_change(struct Qdisc *sch,
del_timer(&q->perturb_timer);
if (q->perturb_period) {
mod_timer(&q->perturb_timer, jiffies + q->perturb_period);
- q->perturbation = prandom_u32();
+ get_random_bytes(&q->perturbation, sizeof(q->perturbation));
}
sch_tree_unlock(sch);
kfree(p);
@@ -745,7 +747,7 @@ static int sfq_init(struct Qdisc *sch, s
q->quantum = psched_mtu(qdisc_dev(sch));
q->scaled_quantum = SFQ_ALLOT_SIZE(q->quantum);
q->perturb_period = 0;
- q->perturbation = prandom_u32();
+ get_random_bytes(&q->perturbation, sizeof(q->perturbation));

if (opt) {
int err = sfq_change(sch, opt);

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