[PATCH 6.18 071/277] netfilter: ctnetlink: zero expect NAT fields when CTA_EXPECT_NAT absent

Greg Kroah-Hartman
2026-04-08T18:30:26Z

From: Qi Tang <tpluszz77@gmail.com>

[ Upstream commit 35177c6877134a21315f37d57a5577846225623e ]

ctnetlink_alloc_expect() allocates expectations from a non-zeroing
slab cache via nf_ct_expect_alloc(). When CTA_EXPECT_NAT is not
present in the netlink message, saved_addr and saved_proto are
never initialized. Stale data from a previous slab occupant can
then be dumped to userspace by ctnetlink_exp_dump_expect(), which
checks these fields to decide whether to emit CTA_EXPECT_NAT.

The safe sibling nf_ct_expect_init(), used by the packet path,
explicitly zeroes these fields.

Zero saved_addr, saved_proto and dir in the else branch, guarded
by IS_ENABLED(CONFIG_NF_NAT) since these fields only exist when
NAT is enabled.

Confirmed by priming the expect slab with NAT-bearing expectations,
freeing them, creating a new expectation without CTA_EXPECT_NAT,
and observing that the ctnetlink dump emits a spurious
CTA_EXPECT_NAT containing stale data from the prior allocation.

Fixes: 076a0ca02644 ("netfilter: ctnetlink: add NAT support for expectations")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Qi Tang <tpluszz77@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/netfilter/nf_conntrack_netlink.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
index 768f741f59afe..82d5abae0ad1f 100644
--- a/net/netfilter/nf_conntrack_netlink.c
+++ b/net/netfilter/nf_conntrack_netlink.c
@@ -3576,6 +3576,12 @@ ctnetlink_alloc_expect(const struct nlattr * const cda[], struct nf_conn *ct,
exp, nf_ct_l3num(ct));
if (err < 0)
goto err_out;
+#if IS_ENABLED(CONFIG_NF_NAT)
+ } else {
+ memset(&exp->saved_addr, 0, sizeof(exp->saved_addr));
+ memset(&exp->saved_proto, 0, sizeof(exp->saved_proto));
+ exp->dir = 0;
+#endif
}
return exp;
err_out:
--
2.53.0