diff options
authorPhil Sutter <>2020-02-11 16:52:59 +0100
committerPhil Sutter <>2020-02-12 15:15:10 +0100
commit8e76391096f12212985c401ee83a67990aa27a29 (patch)
parente179e87a1179e272a9bdabb0220b17d61d099ee3 (diff)
xtables-restore: fix for --noflush and empty lines
Lookahead buffer used for cache requirements estimate in restore --noflush separates individual lines with nul-chars. Two consecutive nul-chars are interpreted as end of buffer and remaining buffer content is skipped. Sadly, reading an empty line (i.e., one containing a newline character only) caused double nul-chars to appear in buffer as well, leading to premature stop when reading cached lines from buffer. To fix that, make use of xtables_restore_parse_line() skipping empty lines without calling strtok() and just leave the newline character in place. A more intuitive approach, namely skipping empty lines while buffering, is deliberately not chosen as that would cause wrong values in 'line' variable. Closes: Fixes: 09cb517949e69 ("xtables-restore: Improve performance of --noflush operation") Signed-off-by: Phil Sutter <> Acked-by: Arturo Borrero Gonzalez <>
2 files changed, 21 insertions, 3 deletions
diff --git a/iptables/tests/shell/testcases/ipt-restore/0011-noflush-empty-line_0 b/iptables/tests/shell/testcases/ipt-restore/0011-noflush-empty-line_0
new file mode 100755
index 00000000..bea1a690
--- /dev/null
+++ b/iptables/tests/shell/testcases/ipt-restore/0011-noflush-empty-line_0
@@ -0,0 +1,16 @@
+#!/bin/bash -e
+# make sure empty lines won't break --noflush
+cat <<EOF | $XT_MULTI iptables-restore --noflush
+# just a comment followed by innocent empty line
+target prot opt source destination
+ACCEPT all -- '
+diff -u <(echo "$EXPECT") <($XT_MULTI iptables -n -L FORWARD)
diff --git a/iptables/xtables-restore.c b/iptables/xtables-restore.c
index 63cc15ce..fb2ac8b5 100644
--- a/iptables/xtables-restore.c
+++ b/iptables/xtables-restore.c
@@ -293,11 +293,13 @@ void xtables_restore_parse(struct nft_handle *h,
while (fgets(buffer, sizeof(buffer), p->in)) {
size_t blen = strlen(buffer);
- /* drop trailing newline; xtables_restore_parse_line()
+ /* Drop trailing newline; xtables_restore_parse_line()
* uses strtok() which replaces them by nul-characters,
* causing unpredictable string delimiting in
- * preload_buffer */
- if (buffer[blen - 1] == '\n')
+ * preload_buffer.
+ * Unless this is an empty line which would fold into a
+ * spurious EoB indicator (double nul-char). */
+ if (buffer[blen - 1] == '\n' && blen > 1)
buffer[blen - 1] = '\0';