[PATCH 2/2] ip_frag: randomize hash seed

[Stephen Hemminger]

Both ipv4_frag_hash() and ipv6_frag_hash() use CRC32 (x86/ARM)
or jhash with a fixed, publicly known prime seed (0xeaad8405).
An attacker who can send crafted IP fragments can precompute hash
collisions, causing all fragments to land in the same bucket.
After bucket_entries concurrent flows collide, new flows are  dropped.

Fix by using a random hash seed added at table creation time.

Fixes: 416707812c03 ("ip_frag: refactor reassembly code into a proper library")
Cc: stable at dpdk.org
Signed-off-by: Stephen Hemminger <stephen at networkplumber.org>
---
 lib/ip_frag/ip_frag_internal.c   | 18 ++++++++----------
 lib/ip_frag/ip_reassembly.h      |  1 +
 lib/ip_frag/rte_ip_frag_common.c |  1 +
 3 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/lib/ip_frag/ip_frag_internal.c b/lib/ip_frag/ip_frag_internal.c
index 7cbef647df..382f42d0e1 100644
--- a/lib/ip_frag/ip_frag_internal.c
+++ b/lib/ip_frag/ip_frag_internal.c
@@ -9,8 +9,6 @@
 
 #include "ip_frag_common.h"
 
-#define	PRIME_VALUE	0xeaad8405
-
 #define	IP_FRAG_TBL_POS(tbl, sig)	\
 	((tbl)->pkt + ((sig) & (tbl)->entry_mask))
 
@@ -38,7 +36,7 @@ ip_frag_tbl_reuse(struct rte_ip_frag_tbl *tbl, struct rte_ip_frag_death_row *dr,
 
 
 static inline void
-ipv4_frag_hash(const struct ip_frag_key *key, uint32_t *v1, uint32_t *v2)
+ipv4_frag_hash(const struct ip_frag_key *key, uint32_t *v1, uint32_t *v2, uint32_t seed)
 {
 	uint32_t v;
 	const uint32_t *p;
@@ -46,12 +44,12 @@ ipv4_frag_hash(const struct ip_frag_key *key, uint32_t *v1, uint32_t *v2)
 	p = (const uint32_t *)&key->src_dst;
 
 #if defined(RTE_ARCH_X86) || defined(RTE_ARCH_ARM64)
-	v = rte_hash_crc_4byte(p[0], PRIME_VALUE);
+	v = rte_hash_crc_4byte(p[0], seed);
 	v = rte_hash_crc_4byte(p[1], v);
 	v = rte_hash_crc_4byte(key->id, v);
 #else
 
-	v = rte_jhash_3words(p[0], p[1], key->id, PRIME_VALUE);
+	v = rte_jhash_3words(p[0], p[1], key->id, seed);
 #endif /* RTE_ARCH_X86 */
 
 	*v1 =  v;
@@ -59,7 +57,7 @@ ipv4_frag_hash(const struct ip_frag_key *key, uint32_t *v1, uint32_t *v2)
 }
 
 static inline void
-ipv6_frag_hash(const struct ip_frag_key *key, uint32_t *v1, uint32_t *v2)
+ipv6_frag_hash(const struct ip_frag_key *key, uint32_t *v1, uint32_t *v2, uint32_t seed)
 {
 	uint32_t v;
 	const uint32_t *p;
@@ -67,7 +65,7 @@ ipv6_frag_hash(const struct ip_frag_key *key, uint32_t *v1, uint32_t *v2)
 	p = (const uint32_t *) &key->src_dst;
 
 #if defined(RTE_ARCH_X86) || defined(RTE_ARCH_ARM64)
-	v = rte_hash_crc_4byte(p[0], PRIME_VALUE);
+	v = rte_hash_crc_4byte(p[0], seed);
 	v = rte_hash_crc_4byte(p[1], v);
 	v = rte_hash_crc_4byte(p[2], v);
 	v = rte_hash_crc_4byte(p[3], v);
@@ -78,7 +76,7 @@ ipv6_frag_hash(const struct ip_frag_key *key, uint32_t *v1, uint32_t *v2)
 	v = rte_hash_crc_4byte(key->id, v);
 #else
 
-	v = rte_jhash_3words(p[0], p[1], p[2], PRIME_VALUE);
+	v = rte_jhash_3words(p[0], p[1], p[2], seed);
 	v = rte_jhash_3words(p[3], p[4], p[5], v);
 	v = rte_jhash_3words(p[6], p[7], key->id, v);
 #endif /* RTE_ARCH_X86 */
@@ -301,9 +299,9 @@ ip_frag_lookup(struct rte_ip_frag_tbl *tbl,
 
 	/* different hashing methods for IPv4 and IPv6 */
 	if (key->key_len == IPV4_KEYLEN)
-		ipv4_frag_hash(key, &sig1, &sig2);
+		ipv4_frag_hash(key, &sig1, &sig2, tbl->seed);
 	else
-		ipv6_frag_hash(key, &sig1, &sig2);
+		ipv6_frag_hash(key, &sig1, &sig2, tbl->seed);
 
 	p1 = IP_FRAG_TBL_POS(tbl, sig1);
 	p2 = IP_FRAG_TBL_POS(tbl, sig2);
diff --git a/lib/ip_frag/ip_reassembly.h b/lib/ip_frag/ip_reassembly.h
index 54afed5417..9e1666ef67 100644
--- a/lib/ip_frag/ip_reassembly.h
+++ b/lib/ip_frag/ip_reassembly.h
@@ -79,6 +79,7 @@ struct rte_ip_frag_tbl {
 	uint32_t bucket_entries; /* hash associativity. */
 	uint32_t nb_entries;     /* total size of the table. */
 	uint32_t nb_buckets;     /* num of associativity lines. */
+	uint32_t seed;		 /* hash function init value */
 	struct ip_frag_pkt *last;     /* last used entry. */
 	struct ip_pkt_list lru;       /* LRU list for table entries. */
 	struct ip_frag_tbl_stat stat; /* statistics counters. */
diff --git a/lib/ip_frag/rte_ip_frag_common.c b/lib/ip_frag/rte_ip_frag_common.c
index 79ac45289b..00bf9476de 100644
--- a/lib/ip_frag/rte_ip_frag_common.c
+++ b/lib/ip_frag/rte_ip_frag_common.c
@@ -79,6 +79,7 @@ rte_ip_frag_table_create(uint32_t bucket_num, uint32_t bucket_entries,
 	tbl->nb_buckets = bucket_num;
 	tbl->bucket_entries = bucket_entries;
 	tbl->entry_mask = (tbl->nb_entries - 1) & ~(tbl->bucket_entries  - 1);
+	tbl->seed = rte_rand();
 
 	TAILQ_INIT(&(tbl->lru));
 	return tbl;
-- 
2.53.0