net/flow_dissector: switch to siphash

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@google.com>
Reported-by: Jonathan Berger <jonathann1@walla.com>
Reported-by: Amit Klein <aksecurity@gmail.com>
Reported-by: Benny Pinkas <benny@pinkas.net>
Cc: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 7914fdaf4226694652da46becdac5747dca97687..a391147c03d4090252117e106a0df8f612955634 100644 (file)
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1354,7 +1354,8 @@ static inline __u32 skb_get_hash_flowi6(struct sk_buff *skb, const struct 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)
 {

diff --git a/include/net/flow_dissector.h b/include/net/flow_dissector.h
index 90bd210be06075818a8ba3213006e16eb610c602..5cd12276ae21a52006debcd846c85be1b04bf596 100644 (file)
--- 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;

diff --git a/include/net/fq.h b/include/net/fq.h
index d126b5d2026155aa7311ea82ce609122c6da45e0..2ad85e68304142fc3193e8a2c4dc1cfb4cca821a 100644 (file)
--- 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;

diff --git a/include/net/fq_impl.h b/include/net/fq_impl.h
index be40a4b327e3d1d51f15f29b45216b39e7d1f42e..107c0d700ed6ffd03cd1dc835f086eb989adbed3 100644 (file)
--- 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 flows_cnt)
        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 */

diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index 7c09d87d3269e4d01fd895c595a3a6e67d350685..68eda10d0680749ef07372951debab913449e661 100644 (file)
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -1350,30 +1350,21 @@ 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));
 
@@ -1388,7 +1379,7 @@ static inline size_t flow_keys_hash_length(const struct flow_keys *flow)
                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)
@@ -1454,14 +1445,15 @@ static inline void __flow_hash_consistentify(struct flow_keys *keys)
        }
 }
 
-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;
 
@@ -1471,12 +1463,13 @@ static inline u32 __flow_hash_from_keys(struct flow_keys *keys, u32 keyval)
 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);
@@ -1524,7 +1517,7 @@ u32 __skb_get_hash_symmetric(const struct sk_buff *skb)
                           &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);
 
@@ -1544,13 +1537,14 @@ 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;
 

diff --git a/net/sched/sch_hhf.c b/net/sched/sch_hhf.c
index 23cd1c873a2cfc24b907a8177e71dd68b0939701..be35f03b657b1eb10d224594981aa44e1776801c 100644 (file)
--- a/net/sched/sch_hhf.c
+++ b/net/sched/sch_hhf.c
@@ -5,11 +5,11 @@
  * Copyright (C) 2013 Nandita Dukkipati <nanditad@google.com>
  */
 
-#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(struct sk_buff *skb, struct Qdisc *sch)
        }
 
        /* 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, struct nlattr *opt,
 
        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);
 

diff --git a/net/sched/sch_sfb.c b/net/sched/sch_sfb.c
index d448fe3068e5b9f0b35a37d921ab5a74350dc155..4074c50ac3d73100dd82bd631c127326ff49f355 100644 (file)
--- 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, u32 *avgpm_r, const struct sfb_sched_da
 
 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 *skb, struct Qdisc *sch,
                /* 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 *skb, struct Qdisc *sch,
                /* 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;

diff --git a/net/sched/sch_sfq.c b/net/sched/sch_sfq.c
index 68404a9d2ce426f7027d83f0adde634cb031ef4a..c787d4d46017b4b41b8eb6d41f2b0a44560ff5bf 100644 (file)
--- 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_head(struct sfq_sched_data *q, sfq_index
 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 timer_list *t)
        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, struct nlattr *opt)
        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, struct nlattr *opt,
        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);