From: Daniel Borkmann <daniel@iogearbox.net>
Date: Wed, 22 Aug 2018 23:49:37 +0200
Subject: bpf: use per htab salt for bucket hash
Git-commit: c0203475765f827e7b2eaf0a87222d0766e2cc4b
Patch-mainline: v4.19-rc2
References: git-fixes

All BPF hash and LRU maps currently have a known and global seed
we feed into jhash() which is 0. This is suboptimal, thus fix it
by generating a random seed upon hashtab setup time which we can
later on feed into jhash() on lookup, update and deletions.

Fixes: 0f8e4bd8a1fc8 ("bpf: add hashtable type of eBPF maps")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Reviewed-by: Eduardo Valentin <eduval@amazon.com>
Acked-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
---
 kernel/bpf/hashtab.c |   23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -14,6 +14,7 @@
 #include <linux/jhash.h>
 #include <linux/filter.h>
 #include <linux/rculist_nulls.h>
+#include <linux/random.h>
 #include "percpu_freelist.h"
 #include "bpf_lru_list.h"
 #include "map_in_map.h"
@@ -35,6 +36,7 @@ struct bpf_htab {
 	atomic_t count;	/* number of elements in this hashtable */
 	u32 n_buckets;	/* number of hash buckets */
 	u32 elem_size;	/* size of each element in bytes */
+	u32 hashrnd;
 };
 
 /* each htab element is struct htab_elem + key + value */
@@ -348,6 +350,7 @@ static struct bpf_map *htab_map_alloc(un
 	if (!htab->buckets)
 		goto free_htab;
 
+	htab->hashrnd = get_random_int();
 	for (i = 0; i < htab->n_buckets; i++) {
 		INIT_HLIST_NULLS_HEAD(&htab->buckets[i].head, i);
 		raw_spin_lock_init(&htab->buckets[i].lock);
@@ -379,9 +382,9 @@ free_htab:
 	return ERR_PTR(err);
 }
 
-static inline u32 htab_map_hash(const void *key, u32 key_len)
+static inline u32 htab_map_hash(const void *key, u32 key_len, u32 hashrnd)
 {
-	return jhash(key, key_len, 0);
+	return jhash(key, key_len, hashrnd);
 }
 
 static inline struct bucket *__select_bucket(struct bpf_htab *htab, u32 hash)
@@ -447,7 +450,7 @@ static void *__htab_map_lookup_elem(stru
 
 	key_size = map->key_size;
 
-	hash = htab_map_hash(key, key_size);
+	hash = htab_map_hash(key, key_size, htab->hashrnd);
 
 	head = select_bucket(htab, hash);
 
@@ -570,7 +573,7 @@ static int htab_map_get_next_key(struct
 	if (!key)
 		goto find_first_elem;
 
-	hash = htab_map_hash(key, key_size);
+	hash = htab_map_hash(key, key_size, htab->hashrnd);
 
 	head = select_bucket(htab, hash);
 
@@ -796,7 +799,7 @@ static int htab_map_update_elem(struct b
 
 	key_size = map->key_size;
 
-	hash = htab_map_hash(key, key_size);
+	hash = htab_map_hash(key, key_size, htab->hashrnd);
 
 	b = __select_bucket(htab, hash);
 	head = &b->head;
@@ -852,7 +855,7 @@ static int htab_lru_map_update_elem(stru
 
 	key_size = map->key_size;
 
-	hash = htab_map_hash(key, key_size);
+	hash = htab_map_hash(key, key_size, htab->hashrnd);
 
 	b = __select_bucket(htab, hash);
 	head = &b->head;
@@ -917,7 +920,7 @@ static int __htab_percpu_map_update_elem
 
 	key_size = map->key_size;
 
-	hash = htab_map_hash(key, key_size);
+	hash = htab_map_hash(key, key_size, htab->hashrnd);
 
 	b = __select_bucket(htab, hash);
 	head = &b->head;
@@ -970,7 +973,7 @@ static int __htab_lru_percpu_map_update_
 
 	key_size = map->key_size;
 
-	hash = htab_map_hash(key, key_size);
+	hash = htab_map_hash(key, key_size, htab->hashrnd);
 
 	b = __select_bucket(htab, hash);
 	head = &b->head;
@@ -1043,7 +1046,7 @@ static int htab_map_delete_elem(struct b
 
 	key_size = map->key_size;
 
-	hash = htab_map_hash(key, key_size);
+	hash = htab_map_hash(key, key_size, htab->hashrnd);
 	b = __select_bucket(htab, hash);
 	head = &b->head;
 
@@ -1075,7 +1078,7 @@ static int htab_lru_map_delete_elem(stru
 
 	key_size = map->key_size;
 
-	hash = htab_map_hash(key, key_size);
+	hash = htab_map_hash(key, key_size, htab->hashrnd);
 	b = __select_bucket(htab, hash);
 	head = &b->head;