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From f9688b8f6755c3c2eb5c7e2e22ab168d0cb97644 Mon Sep 17 00:00:00 2001
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From: Munehisa Kamata <kamatam@amazon.com>
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Date: Mon, 26 Oct 2015 19:10:52 -0700
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Subject: [PATCH] netfilter: nf_nat_redirect: add missing NULL pointer check
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Upstream commit 94f9cd81436c85d8c3a318ba92e236ede73752fc
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Commit 8b13eddfdf04cbfa561725cfc42d6868fe896f56 ("netfilter: refactor NAT
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redirect IPv4 to use it from nf_tables") has introduced a trivial logic
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change which can result in the following crash.
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BUG: unable to handle kernel NULL pointer dereference at 0000000000000030
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IP: [<ffffffffa033002d>] nf_nat_redirect_ipv4+0x2d/0xa0 [nf_nat_redirect]
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PGD 3ba662067 PUD 3ba661067 PMD 0
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Oops: 0000 [#1] SMP
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Modules linked in: ipv6(E) xt_REDIRECT(E) nf_nat_redirect(E) xt_tcpudp(E) iptable_nat(E) nf_conntrack_ipv4(E) nf_defrag_ipv4(E) nf_nat_ipv4(E) nf_nat(E) nf_conntrack(E) ip_tables(E) x_tables(E) binfmt_misc(E) xfs(E) libcrc32c(E) evbug(E) evdev(E) psmouse(E) i2c_piix4(E) i2c_core(E) acpi_cpufreq(E) button(E) ext4(E) crc16(E) jbd2(E) mbcache(E) dm_mirror(E) dm_region_hash(E) dm_log(E) dm_mod(E)
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CPU: 0 PID: 2536 Comm: ip Tainted: G E 4.1.7-15.23.amzn1.x86_64 #1
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Hardware name: Xen HVM domU, BIOS 4.2.amazon 05/06/2015
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task: ffff8800eb438000 ti: ffff8803ba664000 task.ti: ffff8803ba664000
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[...]
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Call Trace:
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<IRQ>
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[<ffffffffa0334065>] redirect_tg4+0x15/0x20 [xt_REDIRECT]
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[<ffffffffa02e2e99>] ipt_do_table+0x2b9/0x5e1 [ip_tables]
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[<ffffffffa0328045>] iptable_nat_do_chain+0x25/0x30 [iptable_nat]
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[<ffffffffa031777d>] nf_nat_ipv4_fn+0x13d/0x1f0 [nf_nat_ipv4]
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[<ffffffffa0328020>] ? iptable_nat_ipv4_fn+0x20/0x20 [iptable_nat]
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[<ffffffffa031785e>] nf_nat_ipv4_in+0x2e/0x90 [nf_nat_ipv4]
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[<ffffffffa03280a5>] iptable_nat_ipv4_in+0x15/0x20 [iptable_nat]
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[<ffffffff81449137>] nf_iterate+0x57/0x80
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[<ffffffff814491f7>] nf_hook_slow+0x97/0x100
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[<ffffffff814504d4>] ip_rcv+0x314/0x400
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unsigned int
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nf_nat_redirect_ipv4(struct sk_buff *skb,
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...
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{
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...
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rcu_read_lock();
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indev = __in_dev_get_rcu(skb->dev);
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if (indev != NULL) {
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ifa = indev->ifa_list;
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newdst = ifa->ifa_local; <---
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}
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rcu_read_unlock();
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...
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}
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Before the commit, 'ifa' had been always checked before access. After the
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commit, however, it could be accessed even if it's NULL. Interestingly,
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this was once fixed in 2003.
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http://marc.info/?l=netfilter-devel&m=106668497403047&w=2
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In addition to the original one, we have seen the crash when packets that
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need to be redirected somehow arrive on an interface which hasn't been
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yet fully configured.
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This change just reverts the logic to the old behavior to avoid the crash.
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Fixes: 8b13eddfdf04 ("netfilter: refactor NAT redirect IPv4 to use it from nf_tables")
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Signed-off-by: Munehisa Kamata <kamatam@amazon.com>
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Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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---
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net/netfilter/nf_nat_redirect.c | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/net/netfilter/nf_nat_redirect.c b/net/netfilter/nf_nat_redirect.c
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index 97b75f9bfbcd..d43869879fcf 100644
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--- a/net/netfilter/nf_nat_redirect.c
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+++ b/net/netfilter/nf_nat_redirect.c
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@@ -55,7 +55,7 @@ nf_nat_redirect_ipv4(struct sk_buff *skb,
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rcu_read_lock();
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indev = __in_dev_get_rcu(skb->dev);
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- if (indev != NULL) {
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+ if (indev && indev->ifa_list) {
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ifa = indev->ifa_list;
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newdst = ifa->ifa_local;
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}
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--
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2.5.0
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