Re: [PATCH nf] netfilter: nft_set_rbtree: reject expired interval ends

On Mon, Oct 05, 2026 at 11:20:57PM +0200, Pablo Neira Ayuso wrote:

On Mon, Oct 05, 2026 at 08:04:05PM +0000, Jérémy Jean wrote:

quoted

Consider two ranges in a netfilter verdict map:
* keys 10-19 accept packets, and
* keys 30-39 jump to chain 'victim'.
Now, delete the end marker at 20. The lookup array now uses element 30
as the first range's end, so an INTERVAL_END query for key 15 returns
element 30, including its jump verdict and chain pointer. This can make
KASAN reports a UAF after the GC releases reference chain for 30 that
has expired:

  BUG: KASAN: slab-use-after-free in nft_verdict_dump+0xdd/0x110
  Read of size 8 at addr ff110000009dfb58 by task repro/50
  ...
  Call Trace:
  ...
   nft_verdict_dump+0xdd/0x110
   nft_data_dump+0x4d/0x80
   nf_tables_fill_setelem+0x30b/0x8a0
   ? __asan_memcpy+0x3c/0x60
   nf_tables_fill_setelem_info+0x1b0/0x200
   nft_get_set_elem+0x3fd/0x4b0
  ...
  Freed by task 24:
  ...
   kfree+0x1a5/0x280
   nf_tables_trans_destroy_work+0x2cb/0x520

Reject expired endpoints in nft_rbtree_get() before returning them.

Fixes: 2aa34191f06f ("netfilter: nft_set_rbtree: use binary search array in get command")
Cc: <redacted>
Assisted-by: LLM
Signed-off-by: Jérémy Jean <redacted>
---
 net/netfilter/nft_set_rbtree.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/netfilter/nft_set_rbtree.c b/net/netfilter/nft_set_rbtree.c
index 9894832..1fd9cbe 100644
--- a/net/netfilter/nft_set_rbtree.c
+++ b/net/netfilter/nft_set_rbtree.c

@@ -187,6 +187,8 @@ nft_rbtree_get(const struct net *net, const struct nft_set *set,
 	if (flags & NFT_SET_ELEM_INTERVAL_END) {
 		if (!interval->to)
 			return NULL;
+		if (nft_set_elem_expired(interval->to))
+			return ERR_PTR(-ENOENT);

End elements carry no timeout set extension.

And nf_tables_getsetelem() is called under RCU read side lock, and
elements are released after RCU grace period.

This patch is papering the problem.

quoted

 		rbe = container_of(interval->to, struct nft_rbtree_elem, ext);
 	} else {
-- 
2.47.3