[nf-next PATCH] netfilter: nf_tables: exthdr: Add support for existence check

[Phil Sutter]

If NFT_EXTHDR_F_PRESENT is set, exthdr will not copy any header field
data into *dest, but instead set it to 1 if the header is found and 0
otherwise.

Signed-off-by: Phil Sutter <p...@nwl.cc>
---
 include/uapi/linux/netfilter/nf_tables.h |  6 ++++++
 net/netfilter/nft_exthdr.c               | 14 ++++++++++++--
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/netfilter/nf_tables.h 
b/include/uapi/linux/netfilter/nf_tables.h
index b00a05d1ee566..f15696af168ac 100644
--- a/include/uapi/linux/netfilter/nf_tables.h
+++ b/include/uapi/linux/netfilter/nf_tables.h
@@ -704,6 +704,10 @@ enum nft_payload_attributes {
 };
 #define NFTA_PAYLOAD_MAX       (__NFTA_PAYLOAD_MAX - 1)
 
+enum nft_exthdr_flags {
+       NFT_EXTHDR_F_PRESENT = (1 << 0),
+};
+
 /**
  * enum nft_exthdr_attributes - nf_tables IPv6 extension header expression 
netlink attributes
  *
@@ -711,6 +715,7 @@ enum nft_payload_attributes {
  * @NFTA_EXTHDR_TYPE: extension header type (NLA_U8)
  * @NFTA_EXTHDR_OFFSET: extension header offset (NLA_U32)
  * @NFTA_EXTHDR_LEN: extension header length (NLA_U32)
+ * @NFTA_EXTHDR_FLAGS: extension header flags (NLA_U32)
  */
 enum nft_exthdr_attributes {
        NFTA_EXTHDR_UNSPEC,
@@ -718,6 +723,7 @@ enum nft_exthdr_attributes {
        NFTA_EXTHDR_TYPE,
        NFTA_EXTHDR_OFFSET,
        NFTA_EXTHDR_LEN,
+       NFTA_EXTHDR_FLAGS,
        __NFTA_EXTHDR_MAX
 };
 #define NFTA_EXTHDR_MAX                (__NFTA_EXTHDR_MAX - 1)
diff --git a/net/netfilter/nft_exthdr.c b/net/netfilter/nft_exthdr.c
index 47beb3abcc9da..b5b37f211c417 100644
--- a/net/netfilter/nft_exthdr.c
+++ b/net/netfilter/nft_exthdr.c
@@ -23,6 +23,7 @@ struct nft_exthdr {
        u8                      offset;
        u8                      len;
        enum nft_registers      dreg:8;
+       u32                     flags;
 };
 
 static void nft_exthdr_eval(const struct nft_expr *expr,
@@ -35,8 +36,12 @@ static void nft_exthdr_eval(const struct nft_expr *expr,
        int err;
 
        err = ipv6_find_hdr(pkt->skb, &offset, priv->type, NULL, NULL);
-       if (err < 0)
+       if (priv->flags & NFT_EXTHDR_F_PRESENT) {
+               *dest = (err >= 0);
+               return;
+       } else if (err < 0) {
                goto err;
+       }
        offset += priv->offset;
 
        dest[priv->len / NFT_REG32_SIZE] = 0;
@@ -52,6 +57,7 @@ static const struct nla_policy 
nft_exthdr_policy[NFTA_EXTHDR_MAX + 1] = {
        [NFTA_EXTHDR_TYPE]              = { .type = NLA_U8 },
        [NFTA_EXTHDR_OFFSET]            = { .type = NLA_U32 },
        [NFTA_EXTHDR_LEN]               = { .type = NLA_U32 },
+       [NFTA_EXTHDR_FLAGS]             = { .type = NLA_U32 },
 };
 
 static int nft_exthdr_init(const struct nft_ctx *ctx,
@@ -65,7 +71,8 @@ static int nft_exthdr_init(const struct nft_ctx *ctx,
        if (tb[NFTA_EXTHDR_DREG] == NULL ||
            tb[NFTA_EXTHDR_TYPE] == NULL ||
            tb[NFTA_EXTHDR_OFFSET] == NULL ||
-           tb[NFTA_EXTHDR_LEN] == NULL)
+           tb[NFTA_EXTHDR_LEN] == NULL ||
+           tb[NFTA_EXTHDR_FLAGS] == NULL)
                return -EINVAL;
 
        err = nft_parse_u32_check(tb[NFTA_EXTHDR_OFFSET], U8_MAX, &offset);
@@ -80,6 +87,7 @@ static int nft_exthdr_init(const struct nft_ctx *ctx,
        priv->offset = offset;
        priv->len    = len;
        priv->dreg   = nft_parse_register(tb[NFTA_EXTHDR_DREG]);
+       priv->flags  = ntohl(nla_get_u32(tb[NFTA_EXTHDR_FLAGS]));
 
        return nft_validate_register_store(ctx, priv->dreg, NULL,
                                           NFT_DATA_VALUE, priv->len);
@@ -97,6 +105,8 @@ static int nft_exthdr_dump(struct sk_buff *skb, const struct 
nft_expr *expr)
                goto nla_put_failure;
        if (nla_put_be32(skb, NFTA_EXTHDR_LEN, htonl(priv->len)))
                goto nla_put_failure;
+       if (nla_put_be32(skb, NFTA_EXTHDR_FLAGS, htonl(priv->flags)))
+               goto nla_put_failure;
        return 0;
 
 nla_put_failure:
-- 
2.11.0

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