[PATCH net 10/16] netfilter: nft_payload: reject offsets exceeding 65535 bytes

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

From: Florian Westphal <fw@strlen.de>

Large offsets were rejected based on netlink policy, but blamed commit
removed the policy without updating nft_payload_inner_init() to use the
truncation-check helper.

Silent truncation is not a problem, but not wanted either, so add a
check.

Fixes: 077dc4a27579 ("netfilter: nft_payload: extend offset to 65535 bytes")
Signed-off-by: Florian Westphal <fw@strlen.de>
Reviewed-by: Fernando Fernandez Mancera <fmancera@suse.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
 net/netfilter/nft_payload.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/net/netfilter/nft_payload.c b/net/netfilter/nft_payload.c
index ef2a80dfc68f..345eff140d56 100644
--- a/net/netfilter/nft_payload.c
+++ b/net/netfilter/nft_payload.c
@@ -224,11 +224,17 @@ static int nft_payload_init(const struct nft_ctx *ctx,
 			    const struct nlattr * const tb[])
 {
 	struct nft_payload *priv = nft_expr_priv(expr);
+	u32 offset;
+	int err;
 
 	priv->base   = ntohl(nla_get_be32(tb[NFTA_PAYLOAD_BASE]));
-	priv->offset = ntohl(nla_get_be32(tb[NFTA_PAYLOAD_OFFSET]));
 	priv->len    = ntohl(nla_get_be32(tb[NFTA_PAYLOAD_LEN]));
 
+	err = nft_parse_u32_check(tb[NFTA_PAYLOAD_OFFSET], U16_MAX, &offset);
+	if (err < 0)
+		return err;
+	priv->offset = offset;
+
 	return nft_parse_register_store(ctx, tb[NFTA_PAYLOAD_DREG],
 					&priv->dreg, NULL, NFT_DATA_VALUE,
 					priv->len);
@@ -621,7 +627,8 @@ static int nft_payload_inner_init(const struct nft_ctx *ctx,
 				  const struct nlattr * const tb[])
 {
 	struct nft_payload *priv = nft_expr_priv(expr);
-	u32 base;
+	u32 base, offset;
+	int err;
 
 	if (!tb[NFTA_PAYLOAD_BASE] || !tb[NFTA_PAYLOAD_OFFSET] ||
 	    !tb[NFTA_PAYLOAD_LEN] || !tb[NFTA_PAYLOAD_DREG])
@@ -639,8 +646,11 @@ static int nft_payload_inner_init(const struct nft_ctx *ctx,
 	}
 
 	priv->base   = base;
-	priv->offset = ntohl(nla_get_be32(tb[NFTA_PAYLOAD_OFFSET]));
 	priv->len    = ntohl(nla_get_be32(tb[NFTA_PAYLOAD_LEN]));
+	err = nft_parse_u32_check(tb[NFTA_PAYLOAD_OFFSET], U16_MAX, &offset);
+	if (err < 0)
+		return err;
+	priv->offset = offset;
 
 	return nft_parse_register_store(ctx, tb[NFTA_PAYLOAD_DREG],
 					&priv->dreg, NULL, NFT_DATA_VALUE,
-- 
2.47.3