Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

netfilter: iptables: Fix null-ptr-deref in iptable_nat_table_init().

We had a report that iptables-restore sometimes triggered null-ptr-deref at boot time. [0]

The problem is that iptable_nat_table_init() is exposed to user space before the kernel fully initialises netns.

In the small race window, a user could call iptable_nat_table_init() that accesses net_generic(net, iptable_nat_net_id), which is available only after registering iptable_nat_net_ops.

Let's call register_pernet_subsys() before xt_register_template().

[0]: bpfilter: Loaded bpfilter_umh pid 11702 Started bpfilter BUG: kernel NULL pointer dereference, address: 0000000000000013 PF: supervisor write access in kernel mode PF: error_code(0x0002) - not-present page PGD 0 P4D 0 PREEMPT SMP NOPTI CPU: 2 PID: 11879 Comm: iptables-restor Not tainted 6.1.92-99.174.amzn2023.x86_64 #1 Hardware name: Amazon EC2 c6i.4xlarge/, BIOS 1.0 10/16/2017 RIP: 0010:iptable_nat_table_init (net/ipv4/netfilter/iptable_nat.c:87 net/ipv4/netfilter/iptable_nat.c:121) iptable_nat Code: 10 4c 89 f6 48 89 ef e8 0b 19 bb ff 41 89 c4 85 c0 75 38 41 83 c7 01 49 83 c6 28 41 83 ff 04 75 dc 48 8b 44 24 08 48 8b 0c 24 <48> 89 08 4c 89 ef e8 a2 3b a2 cf 48 83 c4 10 44 89 e0 5b 5d 41 5c RSP: 0018:ffffbef902843cd0 EFLAGS: 00010246 RAX: 0000000000000013 RBX: ffff9f4b052caa20 RCX: ffff9f4b20988d80 RDX: 0000000000000000 RSI: 0000000000000064 RDI: ffffffffc04201c0 RBP: ffff9f4b2939…