netfilter: nft_numgen: add number generation offset

Add support of an offset value for incremental counter and random. With
this option the sysadmin is able to start the counter to a certain value
and then apply the generated number.

Example:

	meta mark set numgen inc mod 2 offset 100

This will generate marks with the serie 100, 101, 100, 101, ...

Suggested-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Laura Garcia Liebana <nevola@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

2 files changed, 28 insertions, 6 deletions

diff --git a/include/uapi/linux/netfilter/nf_tables.h b/include/uapi/linux/netfilter/nf_tables.h
index bc0eb6a1066d..bcfb892ff148 100644
--- a/include/uapi/linux/netfilter/nf_tables.h
+++ b/include/uapi/linux/netfilter/nf_tables.h
@@ -1136,12 +1136,14 @@ enum nft_trace_types {
  * @NFTA_NG_DREG: destination register (NLA_U32)
  * @NFTA_NG_MODULUS: maximum counter value (NLA_U32)
  * @NFTA_NG_TYPE: operation type (NLA_U32)
+ * @NFTA_NG_OFFSET: offset to be added to the counter (NLA_U32)
  */
 enum nft_ng_attributes {
         NFTA_NG_UNSPEC,
         NFTA_NG_DREG,
         NFTA_NG_MODULUS,
         NFTA_NG_TYPE,
+        NFTA_NG_OFFSET,
         __NFTA_NG_MAX
 };
 #define NFTA_NG_MAX     (__NFTA_NG_MAX - 1)
diff --git a/net/netfilter/nft_numgen.c b/net/netfilter/nft_numgen.c
index f173ebec30a7..55bc5ab78d4a 100644
--- a/net/netfilter/nft_numgen.c
+++ b/net/netfilter/nft_numgen.c
@@ -23,6 +23,7 @@ struct nft_ng_inc {
         enum nft_registers      dreg:8;
         u32                     modulus;
         atomic_t                counter;
+        u32                     offset;
 };
 
 static void nft_ng_inc_eval(const struct nft_expr *expr,
@@ -37,13 +38,14 @@ static void nft_ng_inc_eval(const struct nft_expr *expr,
                 nval = (oval + 1 < priv->modulus) ? oval + 1 : 0;
         } while (atomic_cmpxchg(&priv->counter, oval, nval) != oval);
 
-        regs->data[priv->dreg] = nval;
+        regs->data[priv->dreg] = nval + priv->offset;
 }
 
 static const struct nla_policy nft_ng_policy[NFTA_NG_MAX + 1] = {
         [NFTA_NG_DREG]          = { .type = NLA_U32 },
         [NFTA_NG_MODULUS]       = { .type = NLA_U32 },
         [NFTA_NG_TYPE]          = { .type = NLA_U32 },
+        [NFTA_NG_OFFSET]        = { .type = NLA_U32 },
 };
 
 static int nft_ng_inc_init(const struct nft_ctx *ctx,
@@ -52,10 +54,16 @@ static int nft_ng_inc_init(const struct nft_ctx *ctx,
 {
         struct nft_ng_inc *priv = nft_expr_priv(expr);
 
+        if (tb[NFTA_NG_OFFSET])
+                priv->offset = ntohl(nla_get_be32(tb[NFTA_NG_OFFSET]));
+
         priv->modulus = ntohl(nla_get_be32(tb[NFTA_NG_MODULUS]));
         if (priv->modulus == 0)
                 return -ERANGE;
 
+        if (priv->offset + priv->modulus - 1 < priv->offset)
+                return -EOVERFLOW;
+
         priv->dreg = nft_parse_register(tb[NFTA_NG_DREG]);
         atomic_set(&priv->counter, 0);
 
@@ -64,7 +72,7 @@ static int nft_ng_inc_init(const struct nft_ctx *ctx,
 }
 
 static int nft_ng_dump(struct sk_buff *skb, enum nft_registers dreg,
-                       u32 modulus, enum nft_ng_types type)
+                       u32 modulus, enum nft_ng_types type, u32 offset)
 {
         if (nft_dump_register(skb, NFTA_NG_DREG, dreg))
                 goto nla_put_failure;
@@ -72,6 +80,8 @@ static int nft_ng_dump(struct sk_buff *skb, enum nft_registers dreg,
                 goto nla_put_failure;
         if (nla_put_be32(skb, NFTA_NG_TYPE, htonl(type)))
                 goto nla_put_failure;
+        if (nla_put_be32(skb, NFTA_NG_OFFSET, htonl(offset)))
+                goto nla_put_failure;
 
         return 0;
 
@@ -83,12 +93,14 @@ static int nft_ng_inc_dump(struct sk_buff *skb, const struct nft_expr *expr)
 {
         const struct nft_ng_inc *priv = nft_expr_priv(expr);
 
-        return nft_ng_dump(skb, priv->dreg, priv->modulus, NFT_NG_INCREMENTAL);
+        return nft_ng_dump(skb, priv->dreg, priv->modulus, NFT_NG_INCREMENTAL,
+                           priv->offset);
 }
 
 struct nft_ng_random {
         enum nft_registers      dreg:8;
         u32                     modulus;
+        u32                     offset;
 };
 
 static void nft_ng_random_eval(const struct nft_expr *expr,
@@ -97,9 +109,10 @@ static void nft_ng_random_eval(const struct nft_expr *expr,
 {
         struct nft_ng_random *priv = nft_expr_priv(expr);
         struct rnd_state *state = this_cpu_ptr(&nft_numgen_prandom_state);
+        u32 val;
 
-        regs->data[priv->dreg] = reciprocal_scale(prandom_u32_state(state),
-                                                  priv->modulus);
+        val = reciprocal_scale(prandom_u32_state(state), priv->modulus);
+        regs->data[priv->dreg] = val + priv->offset;
 }
 
 static int nft_ng_random_init(const struct nft_ctx *ctx,
@@ -108,10 +121,16 @@ static int nft_ng_random_init(const struct nft_ctx *ctx,
 {
         struct nft_ng_random *priv = nft_expr_priv(expr);
 
+        if (tb[NFTA_NG_OFFSET])
+                priv->offset = ntohl(nla_get_be32(tb[NFTA_NG_OFFSET]));
+
         priv->modulus = ntohl(nla_get_be32(tb[NFTA_NG_MODULUS]));
         if (priv->modulus == 0)
                 return -ERANGE;
 
+        if (priv->offset + priv->modulus - 1 < priv->offset)
+                return -EOVERFLOW;
+
         prandom_init_once(&nft_numgen_prandom_state);
 
         priv->dreg = nft_parse_register(tb[NFTA_NG_DREG]);
@@ -124,7 +143,8 @@ static int nft_ng_random_dump(struct sk_buff *skb, const struct nft_expr *expr)
 {
         const struct nft_ng_random *priv = nft_expr_priv(expr);
 
-        return nft_ng_dump(skb, priv->dreg, priv->modulus, NFT_NG_RANDOM);
+        return nft_ng_dump(skb, priv->dreg, priv->modulus, NFT_NG_RANDOM,
+                           priv->offset);
 }
 
 static struct nft_expr_type nft_ng_type;