segtree: don't remove nul-root element from interval set

Check from the delinearize set element path if the nul-root element
already exists in the interval set. Hence, the element insertion path
skips the implicit nul-root interval insertion.

Under some circunstances, nft bogusly fails to delete the last element
of the interval set and to create an element in an existing empty
internal set. This patch includes a test that reproduces the issue.

Fixes: 4935a0d561b5 ("segtree: special handling for the first non-matching segment")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/rule.h b/include/rule.h
index 0b2eba37..dadeb4b9 100644
--- a/include/rule.h
+++ b/include/rule.h
@@ -307,6 +307,7 @@ struct set {
 	struct expr		*init;
 	struct expr		*rg_cache;
 	uint32_t		policy;
+	bool			root;
 	bool			automerge;
 	struct {
 		uint32_t	size;