[PATCH 6.1 167/312] netfilter: nf_conntrack_helper: pass helper to expect cleanup

Greg Kroah-Hartman
2026-04-08T18:14:01Z

From: Qi Tang <tpluszz77@gmail.com>

[ Upstream commit a242a9ae58aa46ff7dae51ce64150a93957abe65 ]

nf_conntrack_helper_unregister() calls nf_ct_expect_iterate_destroy()
to remove expectations belonging to the helper being unregistered.
However, it passes NULL instead of the helper pointer as the data
argument, so expect_iter_me() never matches any expectation and all
of them survive the cleanup.

After unregister returns, nfnl_cthelper_del() frees the helper
object immediately. Subsequent expectation dumps or packet-driven
init_conntrack() calls then dereference the freed exp->helper,
causing a use-after-free.

Pass the actual helper pointer so expectations referencing it are
properly destroyed before the helper object is freed.

BUG: KASAN: slab-use-after-free in string+0x38f/0x430
Read of size 1 at addr ffff888003b14d20 by task poc/103
Call Trace:
string+0x38f/0x430
vsnprintf+0x3cc/0x1170
seq_printf+0x17a/0x240
exp_seq_show+0x2e5/0x560
seq_read_iter+0x419/0x1280
proc_reg_read+0x1ac/0x270
vfs_read+0x179/0x930
ksys_read+0xef/0x1c0
Freed by task 103:
The buggy address is located 32 bytes inside of
freed 192-byte region [ffff888003b14d00, ffff888003b14dc0)

Fixes: ac7b84839003 ("netfilter: expect: add and use nf_ct_expect_iterate helpers")
Signed-off-by: Qi Tang <tpluszz77@gmail.com>
Reviewed-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/netfilter/nf_conntrack_helper.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netfilter/nf_conntrack_helper.c b/net/netfilter/nf_conntrack_helper.c
index 5545016c107db..2a15176731fe8 100644
--- a/net/netfilter/nf_conntrack_helper.c
+++ b/net/netfilter/nf_conntrack_helper.c
@@ -422,7 +422,7 @@ void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
*/
synchronize_rcu();

- nf_ct_expect_iterate_destroy(expect_iter_me, NULL);
+ nf_ct_expect_iterate_destroy(expect_iter_me, me);
nf_ct_iterate_destroy(unhelp, me);
}
EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
--
2.53.0