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From 12852e5c973ef9e5d33c1dc1a21c659f4dc6227b Mon Sep 17 00:00:00 2001
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From: Phil Sutter <psutter@redhat.com>
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Date: Fri, 11 May 2018 15:28:07 +0200
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Subject: [PATCH] extensions: libxt_tcpmss: Detect invalid ranges
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Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1128510
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Upstream Status: iptables commit dbbab0aa328f1
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commit dbbab0aa328f136502373a1031e64eb53fa113e5
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Author: Phil Sutter <phil@nwl.cc>
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Date: Mon Oct 9 15:47:39 2017 +0200
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extensions: libxt_tcpmss: Detect invalid ranges
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Previously, an MSS range of e.g. 65535:1000 was silently accepted but
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would then never match a packet since the kernel checks whether the MSS
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value is greater than or equal to the first *and* less than or equal to
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the second value.
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Detect this as a parameter problem and update the man page accordingly.
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Signed-off-by: Phil Sutter <phil@nwl.cc>
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Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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Signed-off-by: Phil Sutter <psutter@redhat.com>
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---
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extensions/libxt_tcpmss.c | 6 +++++-
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extensions/libxt_tcpmss.man | 2 +-
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2 files changed, 6 insertions(+), 2 deletions(-)
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diff --git a/extensions/libxt_tcpmss.c b/extensions/libxt_tcpmss.c
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index c7c5971716294..bcd357aa3d8e2 100644
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--- a/extensions/libxt_tcpmss.c
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+++ b/extensions/libxt_tcpmss.c
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@@ -27,8 +27,12 @@ static void tcpmss_parse(struct xt_option_call *cb)
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xtables_option_parse(cb);
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mssinfo->mss_min = cb->val.u16_range[0];
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mssinfo->mss_max = mssinfo->mss_min;
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- if (cb->nvals == 2)
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+ if (cb->nvals == 2) {
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mssinfo->mss_max = cb->val.u16_range[1];
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+ if (mssinfo->mss_max < mssinfo->mss_min)
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+ xtables_error(PARAMETER_PROBLEM,
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+ "tcpmss: invalid range given");
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+ }
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if (cb->invert)
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mssinfo->invert = 1;
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}
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diff --git a/extensions/libxt_tcpmss.man b/extensions/libxt_tcpmss.man
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index 8ee715cdbfb07..8253c363418f8 100644
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--- a/extensions/libxt_tcpmss.man
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+++ b/extensions/libxt_tcpmss.man
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@@ -1,4 +1,4 @@
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This matches the TCP MSS (maximum segment size) field of the TCP header. You can only use this on TCP SYN or SYN/ACK packets, since the MSS is only negotiated during the TCP handshake at connection startup time.
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.TP
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[\fB!\fP] \fB\-\-mss\fP \fIvalue\fP[\fB:\fP\fIvalue\fP]
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-Match a given TCP MSS value or range.
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+Match a given TCP MSS value or range. If a range is given, the second \fIvalue\fP must be greater than or equal to the first \fIvalue\fP.
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--
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2.17.0
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