From: Mathias Krause Date: Tue, 28 Apr 2026 09:09:17 +0000 (+0200) Subject: netfilter: nf_nat: avoid invalid nat_net pointer use on failed nf_nat_init() X-Git-Tag: v7.2-rc1~29^2~14^2~13 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=069cfe3de2a5e16069485893cd04665ab769c1d8;p=thirdparty%2Flinux.git netfilter: nf_nat: avoid invalid nat_net pointer use on failed nf_nat_init() We ran into below KASAN splat, which is mostly uninteresting, beside for having nf_nat_register_fn() in the call chain as a cause for the offending access: ================================================================== BUG: KASAN: slab-out-of-bounds in nf_nat_register_fn+0x5f9/0x640 Read of size 8 at addr ffff890031e54c20 by task iptables/9510 CPU: 0 UID: 0 PID: 9510 Comm: iptables Not tainted 6.18.18-grsec-full-20260320181326 #1 PREEMPT(voluntary) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 Call Trace: […] dump_stack_lvl+0xee/0x160 ffff88004117eeb8 […] print_report+0x6e/0x640 ffff88004117eee0 […] ? __phys_addr+0x8e/0x140 ffff88004117eef0 […] ? kasan_addr_to_slab+0x51/0xe0 ffff88004117ef08 […] ? complete_report_info+0xec/0x1c0 ffff88004117ef20 […] ? nf_nat_register_fn+0x5f9/0x640 ffff88004117ef48 […] kasan_report+0xbc/0x140 ffff88004117ef50 […] ? nf_nat_register_fn+0x5f9/0x640 ffff88004117ef90 […] nf_nat_register_fn+0x5f9/0x640 ffff88004117eff8 […] ? nf_nat_icmp_reply_translation+0x6e0/0x6e0 ffff88004117f070 […] nf_tables_register_hook.part.0+0xa0/0x220 ffff88004117f080 […] nf_tables_addchain.constprop.0+0x1054/0x1fc0 ffff88004117f0b8 […] ? nft_chain_lookup.part.0+0x4ce/0xac0 ffff88004117f130 […] ? nf_tables_abort+0x3d80/0x3d80 ffff88004117f190 […] ? nf_tables_dumpreset_obj+0x100/0x100 ffff88004117f1c8 […] ? nft_table_lookup.part.0+0x255/0x300 ffff88004117f310 […] ? nf_tables_newchain+0x21a4/0x2fa0 ffff88004117f358 […] nf_tables_newchain+0x21a4/0x2fa0 ffff88004117f360 […] ? nf_tables_addchain.constprop.0+0x1fc0/0x1fc0 ffff88004117f458 […] ? nla_get_range_signed+0x4a0/0x4a0 ffff88004117f488 […] ? lock_acquire+0x16f/0x320 ffff88004117f490 […] ? find_held_lock+0x3b/0xe0 ffff88004117f4b0 […] ? __nla_parse+0x45/0x80 ffff88004117f500 […] nfnetlink_rcv_batch+0xbca/0x19a0 ffff88004117f550 […] ? nfnetlink_net_exit_batch+0x120/0x120 ffff88004117f618 […] ? __sanitizer_cov_trace_switch+0x63/0xe0 ffff88004117f720 […] ? gr_acl_handle_mmap+0x1c4/0x320 ffff88004117f7c0 […] ? nla_get_range_signed+0x4a0/0x4a0 ffff88004117f7e8 […] ? gr_is_capable+0x6f/0xe0 ffff88004117f830 […] ? __nla_parse+0x45/0x80 ffff88004117f860 […] ? skb_pull+0x103/0x1a0 ffff88004117f880 […] nfnetlink_rcv+0x3db/0x4a0 ffff88004117f8b0 […] ? nfnetlink_rcv_batch+0x19a0/0x19a0 ffff88004117f8d8 […] ? netlink_lookup+0xe2/0x240 ffff88004117f900 […] netlink_unicast+0x74b/0xb00 ffff88004117f930 […] ? netlink_attachskb+0xb20/0xb20 ffff88004117f980 […] ? __check_object_size+0x3e/0xaa0 ffff88004117f998 […] ? security_netlink_send+0x51/0x160 ffff88004117f9c8 […] netlink_sendmsg+0xa03/0x1200 ffff88004117f9f8 […] ? netlink_unicast+0xb00/0xb00 ffff88004117fa70 […] ? netlink_unicast+0xb00/0xb00 ffff88004117fac8 […] ? ____sys_sendmsg+0xe2a/0x1040 ffff88004117faf8 […] ____sys_sendmsg+0xe2a/0x1040 ffff88004117fb00 […] ? kernel_recvmsg+0x300/0x300 ffff88004117fb60 […] ? reacquire_held_locks+0xe9/0x260 ffff88004117fbc8 […] ___sys_sendmsg+0x138/0x200 ffff88004117fbf8 […] ? do_recvmmsg+0x7e0/0x7e0 ffff88004117fc30 […] ? lockdep_hardirqs_on_prepare+0x101/0x1e0 ffff88004117fc50 […] ? lock_acquire+0x16f/0x320 ffff88004117fd20 […] ? lock_acquire+0x16f/0x320 ffff88004117fd58 […] ? find_held_lock+0x3b/0xe0 ffff88004117fd70 […] __sys_sendmsg+0x17a/0x260 ffff88004117fdc8 […] ? __sys_sendmsg_sock+0x80/0x80 ffff88004117fdf0 […] ? syscall_trace_enter+0x15e/0x2c0 ffff88004117fe98 […] do_syscall_64+0x7d/0x400 ffff88004117fec8 […] entry_SYSCALL_64_safe_stack+0x4a/0x60 ffff88004117fef8 ================================================================== The out-of-bounds report, though, is a red herring as it is for an access that shouldn't have happened in the first place. When nf_nat_init() fails to register its BPF kfuncs, it'll unwind and, among others, call unregister_pernet_subsys() to deregister its per-net ops. This makes the previously allocated net id available for reuse by the next caller of register_pernet_subsys(), in our case, synproxy. However, 'nat_net_id' will still hold the previously allocated value. If nf_nat.o gets build as a module, all this doesn't matter. A failed initialization routine makes the module fail to load and any dependent module won't be able to load either. However, if nf_nat.o is built-in, a failing init won't /completely/ make its functionality unavailable to dependent modules, namely the code and static data is still there, free to be called by modules like nft_chain_nat.ko. Case in point, nft_chain_nat registers hooks that'll call into nf_nat which, in our case, failed to initialize and therefore won't have a valid net id nor related net_nat object any more. Code in nf_nat, namely nf_nat_register_fn() and nf_nat_unregister_fn(), still making use of the reallocated net id, lead to a type confusion as the call to net_generic() will no longer return memory belonging to an object suited to fit 'struct nat_net' but 'struct synproxy_net' instead. The latter is only 24 bytes on 64-bit systems, much smaller than struct nat_net which is 176 bytes, perfectly explaining the OOB KASAN report. Detect and handle a failed nf_nat_init() by testing the 'nf_nat_hook' pointer which will be reset to NULL on initialization errors to prevent the usage of an invalid nat_net pointer. As this check is only needed when nf_nat.o is built-in, guard it by '#ifndef MODULE...'. Fixes: cbc1dd5b659f ("netfilter: nf_nat: Fix possible memory leak in nf_nat_init()") Signed-off-by: Mathias Krause Signed-off-by: Pablo Neira Ayuso --- diff --git a/net/netfilter/nf_nat_core.c b/net/netfilter/nf_nat_core.c index 2bbf5163c0e27..63ff6b4d5d214 100644 --- a/net/netfilter/nf_nat_core.c +++ b/net/netfilter/nf_nat_core.c @@ -1181,6 +1181,16 @@ int nf_nat_register_fn(struct net *net, u8 pf, const struct nf_hook_ops *ops, struct nf_hook_ops *nat_ops; int i, ret; +#ifndef MODULE + /* If nf_nat_core is built-in and nf_nat_init() fails, dependent + * modules like nft_chain_nat.ko may still call this function. + * However, nat_net would be invalid, likely pointing to some other + * per-net structure. + */ + if (WARN_ON_ONCE(!nf_nat_hook)) + return -EOPNOTSUPP; +#endif + if (WARN_ON_ONCE(pf >= ARRAY_SIZE(nat_net->nat_proto_net))) return -EINVAL;