[PATCH net 6/9] netfilter: nft_fib: reject fib expression on the netdev egress hook

[Florian Westphal <fw@strlen.de>]

From: Theodor Arsenij Larionov-Trichkine <theodorlarionov@gmail.com>

A fib expression in a netdev egress base chain dereferences nft_in(pkt),
NULL on the transmit path, causing a NULL pointer dereference at eval.
nft_fib_validate() masks the hook with NF_INET_* values, but netdev hook
numbers are a separate enum that aliases them (NF_NETDEV_EGRESS ==
NF_INET_LOCAL_IN), so an egress chain passes validation and then faults.

Add nft_fib_netdev_validate() that limits each result/flag to the netdev
hook where the device it reads exists: the input-device cases (OIF,
OIFNAME, ADDRTYPE with F_IIF) to ingress, the output-device case (ADDRTYPE
with F_OIF) to egress, ADDRTYPE with no device flag to both. Also restrict
nft_fib_validate() to NFPROTO_IPV4/IPV6/INET so its NF_INET_* masks are
not applied to another family's hooks.

Fixes: 42df6e1d221d ("netfilter: Introduce egress hook")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/netfilter-devel/ajxsjcDOnwllMfoR@strlen.de/
Signed-off-by: Theodor Arsenij Larionov-Trichkine <theodorlarionov@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 net/netfilter/nft_fib.c        |  9 +++++++++
 net/netfilter/nft_fib_netdev.c | 29 ++++++++++++++++++++++++++++-
 2 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/net/netfilter/nft_fib.c b/net/netfilter/nft_fib.c
index e048f05694cd..89555380f1c5 100644
--- a/net/netfilter/nft_fib.c
+++ b/net/netfilter/nft_fib.c
@@ -31,6 +31,15 @@ int nft_fib_validate(const struct nft_ctx *ctx, const struct nft_expr *expr)
 	const struct nft_fib *priv = nft_expr_priv(expr);
 	unsigned int hooks;
 
+	switch (ctx->family) {
+	case NFPROTO_IPV4:
+	case NFPROTO_IPV6:
+	case NFPROTO_INET:
+		break;
+	default:
+		return -EOPNOTSUPP;
+	}
+
 	switch (priv->result) {
 	case NFT_FIB_RESULT_OIF:
 	case NFT_FIB_RESULT_OIFNAME:
diff --git a/net/netfilter/nft_fib_netdev.c b/net/netfilter/nft_fib_netdev.c
index 3f3478abd845..5774a7544027 100644
--- a/net/netfilter/nft_fib_netdev.c
+++ b/net/netfilter/nft_fib_netdev.c
@@ -50,6 +50,33 @@ static void nft_fib_netdev_eval(const struct nft_expr *expr,
 	regs->verdict.code = NFT_BREAK;
 }
 
+static int nft_fib_netdev_validate(const struct nft_ctx *ctx,
+				   const struct nft_expr *expr)
+{
+	const struct nft_fib *priv = nft_expr_priv(expr);
+	unsigned int hooks;
+
+	switch (priv->result) {
+	case NFT_FIB_RESULT_OIF:
+	case NFT_FIB_RESULT_OIFNAME:
+		hooks = (1 << NF_NETDEV_INGRESS);
+		break;
+	case NFT_FIB_RESULT_ADDRTYPE:
+		if (priv->flags & NFTA_FIB_F_IIF)
+			hooks = (1 << NF_NETDEV_INGRESS);
+		else if (priv->flags & NFTA_FIB_F_OIF)
+			hooks = (1 << NF_NETDEV_EGRESS);
+		else
+			hooks = (1 << NF_NETDEV_INGRESS) |
+				(1 << NF_NETDEV_EGRESS);
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return nft_chain_validate_hooks(ctx->chain, hooks);
+}
+
 static struct nft_expr_type nft_fib_netdev_type;
 static const struct nft_expr_ops nft_fib_netdev_ops = {
 	.type		= &nft_fib_netdev_type,
@@ -57,7 +84,7 @@ static const struct nft_expr_ops nft_fib_netdev_ops = {
 	.eval		= nft_fib_netdev_eval,
 	.init		= nft_fib_init,
 	.dump		= nft_fib_dump,
-	.validate	= nft_fib_validate,
+	.validate	= nft_fib_netdev_validate,
 };
 
 static struct nft_expr_type nft_fib_netdev_type __read_mostly = {
-- 
2.53.0