src: support for get element command

You need a Linux kernel >= 4.15 to use this feature.

This patch allows us to dump the content of an existing set.

 # nft list ruleset
 table ip x {
        set x {
                type ipv4_addr
                flags interval
                elements = { 1.1.1.1-2.2.2.2, 3.3.3.3,
                             5.5.5.5-6.6.6.6 }
        }
 }

You check if a single element exists in the set:

 # nft get element x x { 1.1.1.5 }
 table ip x {
        set x {
                type ipv4_addr
                flags interval
                elements = { 1.1.1.1-2.2.2.2 }
        }
 }

Output means '1.1.1.5' belongs to the '1.1.1.1-2.2.2.2' interval.

You can also check for intervals:

 # nft get element x x { 1.1.1.1-2.2.2.2 }
 table ip x {
        set x {
                type ipv4_addr
                flags interval
                elements = { 1.1.1.1-2.2.2.2 }
        }
 }

If you try to check for an element that doesn't exist, an error is
displayed.

 # nft get element x x { 1.1.1.0 }
 Error: Could not receive set elements: No such file or directory
 get element x x { 1.1.1.0 }
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

You can also check for multiple elements in one go:

 # nft get element x x { 1.1.1.5, 5.5.5.10 }
 table ip x {
        set x {
                type ipv4_addr
                flags interval
                elements = { 1.1.1.1-2.2.2.2, 5.5.5.5-6.6.6.6 }
        }
 }

You can also use this to fetch the existing timeout for specific
elements, in case you have a set with timeouts in place:

 # nft get element w z { 2.2.2.2 }
 table ip w {
        set z {
                type ipv4_addr
                timeout 30s
                elements = { 2.2.2.2 expires 17s }
        }
 }

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

1 files changed, 31 insertions, 0 deletions

diff --git a/src/evaluate.c b/src/evaluate.c
index 41ba1617..a2c1c728 100644
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -3146,6 +3146,34 @@ static int cmd_evaluate_delete(struct eval_ctx *ctx, struct cmd *cmd)
 	}
 }
 
+static int cmd_evaluate_get(struct eval_ctx *ctx, struct cmd *cmd)
+{
+	struct table *table;
+	struct set *set;
+	int ret;
+
+	ret = cache_update(ctx->nf_sock, ctx->cache, cmd->op, ctx->msgs,
+			   ctx->debug_mask & NFT_DEBUG_NETLINK, ctx->octx);
+	if (ret < 0)
+		return ret;
+
+	switch (cmd->obj) {
+	case CMD_OBJ_SETELEM:
+		table = table_lookup(&cmd->handle, ctx->cache);
+		if (table == NULL)
+			return cmd_error(ctx, "Could not process rule: Table '%s' does not exist",
+					 cmd->handle.table);
+		set = set_lookup(table, cmd->handle.set);
+		if (set == NULL || set->flags & (NFT_SET_MAP | NFT_SET_EVAL))
+			return cmd_error(ctx, "Could not process rule: Set '%s' does not exist",
+					 cmd->handle.set);
+
+		return setelem_evaluate(ctx, &cmd->expr);
+	default:
+		BUG("invalid command object type %u\n", cmd->obj);
+	}
+}
+
 static int cmd_evaluate_list_obj(struct eval_ctx *ctx, const struct cmd *cmd,
 				 uint32_t obj_type)
 {
@@ -3486,6 +3514,7 @@ static const char * const cmd_op_name[] = {
 	[CMD_CREATE]	= "create",
 	[CMD_INSERT]	= "insert",
 	[CMD_DELETE]	= "delete",
+	[CMD_GET]	= "get",
 	[CMD_LIST]	= "list",
 	[CMD_FLUSH]	= "flush",
 	[CMD_RENAME]	= "rename",
@@ -3523,6 +3552,8 @@ int cmd_evaluate(struct eval_ctx *ctx, struct cmd *cmd)
 		return cmd_evaluate_add(ctx, cmd);
 	case CMD_DELETE:
 		return cmd_evaluate_delete(ctx, cmd);
+	case CMD_GET:
+		return cmd_evaluate_get(ctx, cmd);
 	case CMD_LIST:
 		return cmd_evaluate_list(ctx, cmd);
 	case CMD_RESET: