From e2d7ee9c49b582f399ad4ba2da2ee1b3e1f89620 Mon Sep 17 00:00:00 2001
From: Phil Sutter <phil@nwl.cc>
Date: Thu, 12 Oct 2023 17:27:42 +0200
Subject: libiptc: Fix for another segfault due to chain index NULL pointer

Chain rename code missed to adjust the num_chains value which is used to
calculate the number of chain index buckets to allocate during an index
rebuild. So with the right number of chains present, the last chain in a
middle bucket being renamed (and ending up in another bucket) triggers
an index rebuild based on false data. The resulting NULL pointer index
bucket then causes a segfault upon reinsertion.

Closes: https://bugzilla.netfilter.org/show_bug.cgi?id=1713
Fixes: 64ff47cde38e4 ("libiptc: fix chain rename bug in libiptc")

Conflict:NA
Reference:https://git.netfilter.org/iptables/commit/?id=e2d7ee9c49b582f399ad4ba2da2ee1b3e1f89620
---
 .../shell/testcases/chain/0008rename-segfault2_0   | 32 ++++++++++++++++++++++
 libiptc/libiptc.c                                  |  4 +++
 2 files changed, 36 insertions(+)
 create mode 100755 iptables/tests/shell/testcases/chain/0008rename-segfault2_0

diff --git a/iptables/tests/shell/testcases/chain/0008rename-segfault2_0 b/iptables/tests/shell/testcases/chain/0008rename-segfault2_0
new file mode 100755
index 00000000..bc473d25
--- /dev/null
+++ b/iptables/tests/shell/testcases/chain/0008rename-segfault2_0
@@ -0,0 +1,32 @@
+#!/bin/bash
+#
+# Another funny rename bug in libiptc:
+# If there is a chain index bucket with only a single chain in it and it is not
+# the last one and that chain is renamed, a chain index rebuild is triggered.
+# Since TC_RENAME_CHAIN missed to temporarily decrement num_chains value, an
+# extra index is allocated and remains NULL. The following insert of renamed
+# chain then segfaults.
+
+(
+	echo "*filter"
+	# first bucket
+	for ((i = 0; i < 40; i++)); do
+		echo ":chain-a-$i - [0:0]"
+	done
+	# second bucket
+	for ((i = 0; i < 40; i++)); do
+		echo ":chain-b-$i - [0:0]"
+	done
+	# third bucket, just make sure it exists
+	echo ":chain-c-0 - [0:0]"
+	echo "COMMIT"
+) | $XT_MULTI iptables-restore
+
+# rename all chains of the middle bucket
+(
+	echo "*filter"
+	for ((i = 0; i < 40; i++)); do
+		echo "-E chain-b-$i chain-d-$i"
+	done
+	echo "COMMIT"
+) | $XT_MULTI iptables-restore --noflush
diff --git a/libiptc/libiptc.c b/libiptc/libiptc.c
index e4750633..9712a363 100644
--- a/libiptc/libiptc.c
+++ b/libiptc/libiptc.c
@@ -2384,12 +2384,16 @@ int TC_RENAME_CHAIN(const IPT_CHAINLABEL oldname,
 		return 0;
 	}
 
+	handle->num_chains--;
+
 	/* This only unlinks "c" from the list, thus no free(c) */
 	iptcc_chain_index_delete_chain(c, handle);
 
 	/* Change the name of the chain */
 	strncpy(c->name, newname, sizeof(IPT_CHAINLABEL) - 1);
 
+	handle->num_chains++;
+
 	/* Insert sorted into to list again */
 	iptc_insert_chain(handle, c);
 
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