From 24d7383ca9e7f056153cc305ee16fa9fd8580909 Mon Sep 17 00:00:00 2001
From: Phil Sutter <phil@nwl.cc>
Date: Wed, 9 Jun 2021 15:49:52 +0200
Subject: [PATCH] segtree: Fix segfault when restoring a huge interval set

Restoring a set of IPv4 prefixes with about 1.1M elements crashes nft as
set_to_segtree() exhausts the stack. Prevent this by allocating the
pointer array on heap and make sure it is freed before returning to
caller.

With this patch in place, restoring said set succeeds with allocation of
about 3GB of memory, according to valgrind.

Signed-off-by: Phil Sutter <phil@nwl.cc>
(cherry picked from commit baecd1cf26851a4c5b7d469206a488f14fe5b147)
---
 src/segtree.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/src/segtree.c b/src/segtree.c
index 9aa39e52d8a09..163a7bb755f9c 100644
--- a/src/segtree.c
+++ b/src/segtree.c
@@ -429,10 +429,10 @@ static int set_to_segtree(struct list_head *msgs, struct set *set,
 			  struct expr *init, struct seg_tree *tree,
 			  bool add, bool merge)
 {
-	struct elementary_interval *intervals[init->size];
+	struct elementary_interval **intervals;
 	struct expr *i, *next;
 	unsigned int n;
-	int err;
+	int err = 0;
 
 	/* We are updating an existing set with new elements, check if the new
 	 * interval overlaps with any of the existing ones.
@@ -443,6 +443,7 @@ static int set_to_segtree(struct list_head *msgs, struct set *set,
 			return err;
 	}
 
+	intervals = xmalloc_array(init->size, sizeof(intervals[0]));
 	n = expr_to_intervals(init, tree->keylen, intervals);
 
 	list_for_each_entry_safe(i, next, &init->expressions, list) {
@@ -461,10 +462,11 @@ static int set_to_segtree(struct list_head *msgs, struct set *set,
 	for (n = 0; n < init->size; n++) {
 		err = ei_insert(msgs, tree, intervals[n], merge);
 		if (err < 0)
-			return err;
+			break;
 	}
 
-	return 0;
+	xfree(intervals);
+	return err;
 }
 
 static bool segtree_needs_first_segment(const struct set *set,
-- 
2.33.0