[PATCH -stable,4.19.x 07/40] netfilter: nft_set_rbtree: fix null deref on element insertion

Pablo Neira Ayuso
2024-06-13T01:02:23Z

commit 61ae320a29b0540c16931816299eb86bf2b66c08 upstream.

There is no guarantee that rb_prev() will not return NULL in nft_rbtree_gc_elem():

general protection fault, probably for non-canonical address 0xdffffc0000000003: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000018-0x000000000000001f]
nft_add_set_elem+0x14b0/0x2990
nf_tables_newsetelem+0x528/0xb30

Furthermore, there is a possible use-after-free while iterating,
'node' can be free'd so we need to cache the next value to use.

Fixes: c9e6978e2725 ("netfilter: nft_set_rbtree: Switch to node list walk for overlap detection")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/netfilter/nft_set_rbtree.c | 20 +++++++++++++-------
1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/net/netfilter/nft_set_rbtree.c b/net/netfilter/nft_set_rbtree.c
index f8d98547df7a..188cb227f31a 100644
--- a/net/netfilter/nft_set_rbtree.c
+++ b/net/netfilter/nft_set_rbtree.c
@@ -223,7 +223,7 @@ static int nft_rbtree_gc_elem(const struct nft_set *__set,
{
struct nft_set *set = (struct nft_set *)__set;
struct rb_node *prev = rb_prev(&rbe->node);
- struct nft_rbtree_elem *rbe_prev;
+ struct nft_rbtree_elem *rbe_prev = NULL;
struct nft_set_gc_batch *gcb;

gcb = nft_set_gc_batch_check(set, NULL, GFP_ATOMIC);
@@ -231,17 +231,21 @@ static int nft_rbtree_gc_elem(const struct nft_set *__set,
return -ENOMEM;

/* search for expired end interval coming before this element. */
- do {
+ while (prev) {
rbe_prev = rb_entry(prev, struct nft_rbtree_elem, node);
if (nft_rbtree_interval_end(rbe_prev))
break;

prev = rb_prev(prev);
- } while (prev != NULL);
+ }
+
+ if (rbe_prev) {
+ rb_erase(&rbe_prev->node, &priv->root);
+ atomic_dec(&set->nelems);
+ }

- rb_erase(&rbe_prev->node, &priv->root);
rb_erase(&rbe->node, &priv->root);
- atomic_sub(2, &set->nelems);
+ atomic_dec(&set->nelems);

nft_set_gc_batch_add(gcb, rbe);
nft_set_gc_batch_complete(gcb);
@@ -270,7 +274,7 @@ static int __nft_rbtree_insert(const struct net *net, const struct nft_set *set,
struct nft_set_ext **ext)
{
struct nft_rbtree_elem *rbe, *rbe_le = NULL, *rbe_ge = NULL;
- struct rb_node *node, *parent, **p, *first = NULL;
+ struct rb_node *node, *next, *parent, **p, *first = NULL;
struct nft_rbtree *priv = nft_set_priv(set);
u8 genmask = nft_genmask_next(net);
int d, err;
@@ -309,7 +313,9 @@ static int __nft_rbtree_insert(const struct net *net, const struct nft_set *set,
* Values stored in the tree are in reversed order, starting from
* highest to lowest value.
*/
- for (node = first; node != NULL; node = rb_next(node)) {
+ for (node = first; node != NULL; node = next) {
+ next = rb_next(node);
+
rbe = rb_entry(node, struct nft_rbtree_elem, node);

if (!nft_set_elem_active(&rbe->ext, genmask))
--
2.30.2