netfilter: nf_tables: upfront validation of data via nft_data_init()

Instead of parsing the data and then validate that type and length are
correct, pass a description of the expected data so it can be validated
upfront before parsing it to bail out earlier.

This patch adds a new .size field to specify the maximum size of the
data area. The .len field is optional and it is used as an input/output
field, it provides the specific length of the expected data in the input
path. If then .len field is not specified, then obtained length from the
netlink attribute is stored. This is required by cmp, bitwise, range and
immediate, which provide no netlink attribute that describes the data
length. The immediate expression uses the destination register type to
infer the expected data type.

Relying on opencoded validation of the expected data might lead to
subtle bugs as described in 7e6bc1f6cabc ("netfilter: nf_tables:
stricter validation of element data").

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 33 insertions, 33 deletions

diff --git a/net/netfilter/nft_bitwise.c b/net/netfilter/nft_bitwise.c
index 83590afe3768..e6e402b247d0 100644
--- a/net/netfilter/nft_bitwise.c
+++ b/net/netfilter/nft_bitwise.c
@@ -93,7 +93,16 @@ static const struct nla_policy nft_bitwise_policy[NFTA_BITWISE_MAX + 1] = {
 static int nft_bitwise_init_bool(struct nft_bitwise *priv,
 				 const struct nlattr *const tb[])
 {
-	struct nft_data_desc mask, xor;
+	struct nft_data_desc mask = {
+		.type	= NFT_DATA_VALUE,
+		.size	= sizeof(priv->mask),
+		.len	= priv->len,
+	};
+	struct nft_data_desc xor = {
+		.type	= NFT_DATA_VALUE,
+		.size	= sizeof(priv->xor),
+		.len	= priv->len,
+	};
 	int err;
 
 	if (tb[NFTA_BITWISE_DATA])
@@ -103,37 +112,30 @@ static int nft_bitwise_init_bool(struct nft_bitwise *priv,
 	    !tb[NFTA_BITWISE_XOR])
 		return -EINVAL;
 
-	err = nft_data_init(NULL, &priv->mask, sizeof(priv->mask), &mask,
-			    tb[NFTA_BITWISE_MASK]);
+	err = nft_data_init(NULL, &priv->mask, &mask, tb[NFTA_BITWISE_MASK]);
 	if (err < 0)
 		return err;
-	if (mask.type != NFT_DATA_VALUE || mask.len != priv->len) {
-		err = -EINVAL;
-		goto err_mask_release;
-	}
 
-	err = nft_data_init(NULL, &priv->xor, sizeof(priv->xor), &xor,
-			    tb[NFTA_BITWISE_XOR]);
+	err = nft_data_init(NULL, &priv->xor, &xor, tb[NFTA_BITWISE_XOR]);
 	if (err < 0)
-		goto err_mask_release;
-	if (xor.type != NFT_DATA_VALUE || xor.len != priv->len) {
-		err = -EINVAL;
-		goto err_xor_release;
-	}
+		goto err_xor_err;
 
 	return 0;
 
-err_xor_release:
-	nft_data_release(&priv->xor, xor.type);
-err_mask_release:
+err_xor_err:
 	nft_data_release(&priv->mask, mask.type);
+
 	return err;
 }
 
 static int nft_bitwise_init_shift(struct nft_bitwise *priv,
 				  const struct nlattr *const tb[])
 {
-	struct nft_data_desc d;
+	struct nft_data_desc desc = {
+		.type	= NFT_DATA_VALUE,
+		.size	= sizeof(priv->data),
+		.len	= sizeof(u32),
+	};
 	int err;
 
 	if (tb[NFTA_BITWISE_MASK] ||
@@ -143,13 +145,12 @@ static int nft_bitwise_init_shift(struct nft_bitwise *priv,
 	if (!tb[NFTA_BITWISE_DATA])
 		return -EINVAL;
 
-	err = nft_data_init(NULL, &priv->data, sizeof(priv->data), &d,
-			    tb[NFTA_BITWISE_DATA]);
+	err = nft_data_init(NULL, &priv->data, &desc, tb[NFTA_BITWISE_DATA]);
 	if (err < 0)
 		return err;
-	if (d.type != NFT_DATA_VALUE || d.len != sizeof(u32) ||
-	    priv->data.data[0] >= BITS_PER_TYPE(u32)) {
-		nft_data_release(&priv->data, d.type);
+
+	if (priv->data.data[0] >= BITS_PER_TYPE(u32)) {
+		nft_data_release(&priv->data, desc.type);
 		return -EINVAL;
 	}
 
@@ -339,22 +340,21 @@ static const struct nft_expr_ops nft_bitwise_ops = {
 static int
 nft_bitwise_extract_u32_data(const struct nlattr * const tb, u32 *out)
 {
-	struct nft_data_desc desc;
 	struct nft_data data;
-	int err = 0;
+	struct nft_data_desc desc = {
+		.type	= NFT_DATA_VALUE,
+		.size	= sizeof(data),
+		.len	= sizeof(u32),
+	};
+	int err;
 
-	err = nft_data_init(NULL, &data, sizeof(data), &desc, tb);
+	err = nft_data_init(NULL, &data, &desc, tb);
 	if (err < 0)
 		return err;
 
-	if (desc.type != NFT_DATA_VALUE || desc.len != sizeof(u32)) {
-		err = -EINVAL;
-		goto err;
-	}
 	*out = data.data[0];
-err:
-	nft_data_release(&data, desc.type);
-	return err;
+
+	return 0;
 }
 
 static int nft_bitwise_fast_init(const struct nft_ctx *ctx,