[PATCH nf 1/1] netfilter: xt_policy: fix strict mode inbound policy matching

[PATCH nf 1/1] netfilter: xt_policy: fix strict mode inbound policy matching

[Ren Wei]

From: Jiexun Wang <wangjiexun2025@gmail.com>

match_policy_in() walks sec_path entries from the last transform to the
first one, but strict policy matching needs to consume info->pol[] in
the same forward order as the rule layout.

Derive the strict-match policy position from the number of transforms
already consumed so that multi-element inbound rules are matched
consistently.

Fixes: df008c91f835 ("net: Allow userns root to control llc, netfilter, netlink, packet, and xfrm")
Cc: stable@kernel.org
Reported-by: Yuan Tan <yuantan098@gmail.com>
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Reported-by: Xin Liu <bird@lzu.edu.cn>
Signed-off-by: Jiexun Wang <wangjiexun2025@gmail.com>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
---
 net/netfilter/xt_policy.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netfilter/xt_policy.c b/net/netfilter/xt_policy.c
index cb6e8279010a..b5fa65558318 100644
--- a/net/netfilter/xt_policy.c
+++ b/net/netfilter/xt_policy.c
@@ -63,7 +63,7 @@ match_policy_in(const struct sk_buff *skb, const struct xt_policy_info *info,
 		return 0;
 
 	for (i = sp->len - 1; i >= 0; i--) {
-		pos = strict ? i - sp->len + 1 : 0;
+		pos = strict ? sp->len - i - 1 : 0;
 		if (pos >= info->len)
 			return 0;
 		e = &info->pol[pos];
-- 
2.34.1

Re: [PATCH nf 1/1] netfilter: xt_policy: fix strict mode inbound policy matching

[Florian Westphal]

Ren Wei <n05ec@lzu.edu.cn> wrote:
> From: Jiexun Wang <wangjiexun2025@gmail.com>
> 
> match_policy_in() walks sec_path entries from the last transform to the
> first one, but strict policy matching needs to consume info->pol[] in
> the same forward order as the rule layout.
> 
> Derive the strict-match policy position from the number of transforms
> already consumed so that multi-element inbound rules are matched
> consistently.

That hints that secpaths with len > 1 do not exist, or at least
have never been used.  This has always been broken.

For the patch

Acked-by: Florian Westphal <fw@strlen.de>