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From 74a62264d4615ae7f76454e7ca406c46a62c7999 Mon Sep 17 00:00:00 2001
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From: Phil Sutter <phil@nwl.cc>
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Date: Mon, 28 Sep 2020 18:57:18 +0200
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Subject: [PATCH] nft: Fix for broken address mask match detection
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Trying to decide whether a bitwise expression is needed to match parts
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of a source or destination address only, add_addr() checks if all bytes
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in 'mask' are 0xff or not. The check is apparently broken though as each
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byte in 'mask' is cast to a signed char before comparing against 0xff,
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therefore the bitwise is always added:
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| # ./bad/iptables-nft -A foo -s 10.0.0.1 -j ACCEPT
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| # ./good/iptables-nft -A foo -s 10.0.0.2 -j ACCEPT
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| # nft --debug=netlink list chain ip filter foo
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| ip filter foo 5
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| [ payload load 4b @ network header + 12 => reg 1 ]
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| [ bitwise reg 1 = (reg=1 & 0xffffffff ) ^ 0x00000000 ]
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| [ cmp eq reg 1 0x0100000a ]
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| [ counter pkts 0 bytes 0 ]
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| [ immediate reg 0 accept ]
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| ip filter foo 6 5
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| [ payload load 4b @ network header + 12 => reg 1 ]
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| [ cmp eq reg 1 0x0200000a ]
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| [ counter pkts 0 bytes 0 ]
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| [ immediate reg 0 accept ]
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| table ip filter {
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| chain foo {
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| ip saddr 10.0.0.1 counter packets 0 bytes 0 accept
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| ip saddr 10.0.0.2 counter packets 0 bytes 0 accept
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| }
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| }
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Fix the cast, safe an extra op and gain 100% performance in ideal cases.
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Fixes: 56859380eb328 ("xtables-compat: avoid unneeded bitwise ops")
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Signed-off-by: Phil Sutter <phil@nwl.cc>
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(cherry picked from commit 72ed608bf1ea550ac13b5b880afc7ad3ffa0afd0)
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Signed-off-by: Phil Sutter <psutter@redhat.com>
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---
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iptables/nft-shared.c | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/iptables/nft-shared.c b/iptables/nft-shared.c
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index 78e422781723f..f60f5df97fb86 100644
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--- a/iptables/nft-shared.c
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+++ b/iptables/nft-shared.c
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@@ -165,7 +165,7 @@ void add_outiface(struct nftnl_rule *r, char *iface, uint32_t op)
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void add_addr(struct nftnl_rule *r, int offset,
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void *data, void *mask, size_t len, uint32_t op)
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{
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- const char *m = mask;
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+ const unsigned char *m = mask;
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int i;
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add_payload(r, offset, len, NFT_PAYLOAD_NETWORK_HEADER);
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--
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2.28.0
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