[PATCH net 07/14] netfilter: nft_compat: ebtables emulation must reject non-bridge targets

[Pablo Neira Ayuso <pablo@netfilter.org>]

From: Florian Westphal <fw@strlen.de>

xtables targets return netfilter verdicts: NF_ACCEPT, NF_DROP, and so
on.  ebtables targets return incompatible verdicts: EBT_ACCEPT,
EBT_DROP, ...   We cannot allow fallback to NFPROTO_UNSPEC.

ebtables doesn't permit this since
11ff7288beb2 ("netfilter: ebtables: reject non-bridge targets")
but that commit missed the nft_compat layer.

Reported-by: Ren Wei <n05ec@lzu.edu.cn>
Reported-by: Wyatt Feng <bronzed_45_vested@icloud.com>
Reported-by: Yuan Tan <yuantan098@gmail.com>
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Reported-by: Zhengchuan Liang <zcliangcn@gmail.com>
Reported-by: Xin Liu <bird@lzu.edu.cn>
Fixes: 0ca743a55991 ("netfilter: nf_tables: add compatibility layer for x_tables")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
 net/netfilter/nft_compat.c | 24 +++++++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/net/netfilter/nft_compat.c b/net/netfilter/nft_compat.c
index 0caa9304d2d0..63864b928259 100644
--- a/net/netfilter/nft_compat.c
+++ b/net/netfilter/nft_compat.c
@@ -397,6 +397,22 @@ static int nft_target_validate(const struct nft_ctx *ctx,
 	return 0;
 }
 
+static int nft_target_bridge_validate(const struct nft_ctx *ctx,
+				      const struct nft_expr *expr)
+{
+	struct xt_target *target = expr->ops->data;
+
+	/* Do not allow UNSPEC to stand-in for NFPROTO_BRIDGE
+	 * targets: they are incompatible.  ebtables targets return
+	 * EBT_ACCEPT, DROP and so on which are not compatible with
+	 * NF_ACCEPT, NF_DROP and so on.
+	 */
+	if (target->family != NFPROTO_BRIDGE)
+		return -ENOENT;
+
+	return nft_target_validate(ctx, expr);
+}
+
 static void __nft_match_eval(const struct nft_expr *expr,
 			     struct nft_regs *regs,
 			     const struct nft_pktinfo *pkt,
@@ -932,13 +948,15 @@ nft_target_select_ops(const struct nft_ctx *ctx,
 	ops->init = nft_target_init;
 	ops->destroy = nft_target_destroy;
 	ops->dump = nft_target_dump;
-	ops->validate = nft_target_validate;
 	ops->data = target;
 
-	if (family == NFPROTO_BRIDGE)
+	if (family == NFPROTO_BRIDGE) {
 		ops->eval = nft_target_eval_bridge;
-	else
+		ops->validate = nft_target_bridge_validate;
+	} else {
 		ops->eval = nft_target_eval_xt;
+		ops->validate = nft_target_validate;
+	}
 
 	return ops;
 err:
-- 
2.47.3