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From 5ea18ea8c0c99f2c71a5eaf32f4fbf6339ce8cc7 Mon Sep 17 00:00:00 2001
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From: Phil Sutter <phil@nwl.cc>
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Date: Tue, 11 Feb 2020 16:52:59 +0100
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Subject: [PATCH] xtables-restore: fix for --noflush and empty lines
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Lookahead buffer used for cache requirements estimate in restore
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--noflush separates individual lines with nul-chars. Two consecutive
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nul-chars are interpreted as end of buffer and remaining buffer content
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is skipped.
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Sadly, reading an empty line (i.e., one containing a newline character
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only) caused double nul-chars to appear in buffer as well, leading to
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premature stop when reading cached lines from buffer.
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To fix that, make use of xtables_restore_parse_line() skipping empty
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lines without calling strtok() and just leave the newline character in
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place. A more intuitive approach, namely skipping empty lines while
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buffering, is deliberately not chosen as that would cause wrong values
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in 'line' variable.
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Closes: https://bugzilla.netfilter.org/show_bug.cgi?id=1400
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Fixes: 09cb517949e69 ("xtables-restore: Improve performance of --noflush operation")
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Signed-off-by: Phil Sutter <phil@nwl.cc>
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Acked-by: Arturo Borrero Gonzalez <arturo@netfilter.org>
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(cherry picked from commit 8e76391096f12212985c401ee83a67990aa27a29)
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Signed-off-by: Phil Sutter <psutter@redhat.com>
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---
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.../ipt-restore/0011-noflush-empty-line_0 | 16 ++++++++++++++++
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iptables/xtables-restore.c | 8 +++++---
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2 files changed, 21 insertions(+), 3 deletions(-)
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create mode 100755 iptables/tests/shell/testcases/ipt-restore/0011-noflush-empty-line_0
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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
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new file mode 100755
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index 0000000000000..bea1a690bb624
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--- /dev/null
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+++ b/iptables/tests/shell/testcases/ipt-restore/0011-noflush-empty-line_0
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@@ -0,0 +1,16 @@
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+#!/bin/bash -e
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+
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+# make sure empty lines won't break --noflush
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+
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+cat <
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+# just a comment followed by innocent empty line
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+
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+*filter
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+-A FORWARD -j ACCEPT
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+COMMIT
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+EOF
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+
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+EXPECT='Chain FORWARD (policy ACCEPT)
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+target prot opt source destination
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+ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 '
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+diff -u <(echo "$EXPECT") <($XT_MULTI iptables -n -L FORWARD)
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diff --git a/iptables/xtables-restore.c b/iptables/xtables-restore.c
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index 63cc15cee9621..fb2ac8b5c12a3 100644
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--- a/iptables/xtables-restore.c
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+++ b/iptables/xtables-restore.c
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@@ -293,11 +293,13 @@ void xtables_restore_parse(struct nft_handle *h,
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while (fgets(buffer, sizeof(buffer), p->in)) {
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size_t blen = strlen(buffer);
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- /* drop trailing newline; xtables_restore_parse_line()
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+ /* Drop trailing newline; xtables_restore_parse_line()
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* uses strtok() which replaces them by nul-characters,
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* causing unpredictable string delimiting in
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- * preload_buffer */
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- if (buffer[blen - 1] == '\n')
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+ * preload_buffer.
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+ * Unless this is an empty line which would fold into a
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+ * spurious EoB indicator (double nul-char). */
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+ if (buffer[blen - 1] == '\n' && blen > 1)
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buffer[blen - 1] = '\0';
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else
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blen++;
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--
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2.24.1
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