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Munehisa Kamata authored
Commit 8b13eddf ("netfilter: refactor NAT redirect IPv4 to use it from nf_tables") has introduced a trivial logic change which can result in the following crash. BUG: unable to handle kernel NULL pointer dereference at 0000000000000030 IP: [<ffffffffa033002d>] nf_nat_redirect_ipv4+0x2d/0xa0 [nf_nat_redirect] PGD 3ba662067 PUD 3ba661067 PMD 0 Oops: 0000 [#1] SMP 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) CPU: 0 PID: 2536 Comm: ip Tainted: G E 4.1.7-15.23.amzn1.x86_64 #1 Hardware name: Xen HVM domU, BIOS 4.2.amazon 05/06/2015 task: ffff8800eb438000 ti: ffff8803ba664000 task.ti: ffff8803ba664000 [...] Call Trace: <IRQ> [<ffffffffa0334065>] redirect_tg4+0x15/0x20 [xt_REDIRECT] [<ffffffffa02e2e99>] ipt_do_table+0x2b9/0x5e1 [ip_tables] [<ffffffffa0328045>] iptable_nat_do_chain+0x25/0x30 [iptable_nat] [<ffffffffa031777d>] nf_nat_ipv4_fn+0x13d/0x1f0 [nf_nat_ipv4] [<ffffffffa0328020>] ? iptable_nat_ipv4_fn+0x20/0x20 [iptable_nat] [<ffffffffa031785e>] nf_nat_ipv4_in+0x2e/0x90 [nf_nat_ipv4] [<ffffffffa03280a5>] iptable_nat_ipv4_in+0x15/0x20 [iptable_nat] [<ffffffff81449137>] nf_iterate+0x57/0x80 [<ffffffff814491f7>] nf_hook_slow+0x97/0x100 [<ffffffff814504d4>] ip_rcv+0x314/0x400 unsigned int nf_nat_redirect_ipv4(struct sk_buff *skb, ... { ... rcu_read_lock(); indev = __in_dev_get_rcu(skb->dev); if (indev != NULL) { ifa = indev->ifa_list; newdst = ifa->ifa_local; <--- } rcu_read_unlock(); ... } Before the commit, 'ifa' had been always checked before access. After the commit, however, it could be accessed even if it's NULL. Interestingly, this was once fixed in 2003. http://marc.info/?l=netfilter-devel&m=106668497403047&w=2 In addition to the original one, we have seen the crash when packets that need to be redirected somehow arrive on an interface which hasn't been yet fully configured. This change just reverts the logic to the old behavior to avoid the crash. Fixes: 8b13eddf ("netfilter: refactor NAT redirect IPv4 to use it from nf_tables") Signed-off-by:
Munehisa Kamata <kamatam@amazon.com> Signed-off-by:
Pablo Neira Ayuso <pablo@netfilter.org>
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