[PATCH 2/2] netfilter: ipset: Fix data race between add and dump in all hash types

[Jozsef Kadlecsik <kadlec@netfilter.org>]

When adding a new entry to the next position in the existing hash bucket,
the position index was incremented too early and parallel dump could
read it before the entry was populated with the value. Move the setting
of the position index after populating the entry.

Reported-by: syzbot+786c889f046e8b003ca6@syzkaller.appspotmail.com
Reported-by: syzbot+1da17e4b41d795df059e@syzkaller.appspotmail.com
Reported-by: syzbot+421c5f3ff8e9493084d9@syzkaller.appspotmail.com
Signed-off-by: Jozsef Kadlecsik <kadlec@netfilter.org>
---
 net/netfilter/ipset/ip_set_hash_gen.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/ipset/ip_set_hash_gen.h b/net/netfilter/ipset/ip_set_hash_gen.h
index b79e5dd2af03..492c2095c11b 100644
--- a/net/netfilter/ipset/ip_set_hash_gen.h
+++ b/net/netfilter/ipset/ip_set_hash_gen.h
@@ -844,7 +844,7 @@ mtype_add(struct ip_set *set, void *value, const struct ip_set_ext *ext,
 	const struct mtype_elem *d = value;
 	struct mtype_elem *data;
 	struct hbucket *n, *old = ERR_PTR(-ENOENT);
-	int i, j = -1, ret;
+	int i, j = -1, npos, ret;
 	bool flag_exist = flags & IPSET_FLAG_EXIST;
 	bool deleted = false, forceadd = false, reuse = false;
 	u32 r, key, multi = 0, elements, maxelem;
@@ -889,6 +889,7 @@ mtype_add(struct ip_set *set, void *value, const struct ip_set_ext *ext,
 			ext_size(AHASH_INIT_SIZE, set->dsize);
 		goto copy_elem;
 	}
+	npos = n->pos;
 	for (i = 0; i < n->pos; i++) {
 		if (!test_bit(i, n->used)) {
 			/* Reuse first deleted entry */
@@ -962,7 +963,7 @@ mtype_add(struct ip_set *set, void *value, const struct ip_set_ext *ext,
 	}
 
 copy_elem:
-	j = n->pos++;
+	j = npos = n->pos + 1;
 	data = ahash_data(n, j, set->dsize);
 copy_data:
 	t->hregion[r].elements++;
@@ -985,6 +986,7 @@ mtype_add(struct ip_set *set, void *value, const struct ip_set_ext *ext,
 	if (SET_WITH_TIMEOUT(set))
 		ip_set_timeout_set(ext_timeout(data, set), ext->timeout);
 	smp_mb__before_atomic();
+	n->pos = npos;
 	set_bit(j, n->used);
 	if (old != ERR_PTR(-ENOENT)) {
 		rcu_assign_pointer(hbucket(t, key), n);
-- 
2.39.5