linux.git/net/ipv6/netfilter, branch master

netfilter: nft_fib_ipv6: bail out of sibling walk if rt got unlinked

2026-06-01T11:43:52+00:00

This was reported by Sashiko [1].

The RCU walk over rt->fib6_siblings can spin forever if rt is unlinked
mid-iteration: rt->fib6_siblings.next still points into the old ring,
so the loop never meets &rt->fib6_siblings as its terminator.

fib6_purge_rt() always does WRITE_ONCE(rt->fib6_nsiblings, 0) before
list_del_rcu(), so readers can use rt->fib6_nsiblings == 0 as the
detach signal. The same pattern is used in fib6_info_uses_dev() and
rt6_nlmsg_size().

[1]: https://sashiko.dev/#/patchset/20260520023411.391233-1-jiayuan.chen%40linux.dev
Suggested-by: Florian Westphal 
Fixes: 1c32b24c234b ("netfilter: nft_fib_ipv6: switch to fib6_lookup")
Signed-off-by: Jiayuan Chen 
Signed-off-by: Florian Westphal 
Signed-off-by: Pablo Neira Ayuso

netfilter: nft_fib_ipv6: handle routes via external nexthop

2026-05-22T10:28:46+00:00

fib6_info has a union:

    union {
        struct list_head fib6_siblings;
        struct list_head nh_list;
    };

Old-style multipath (ip -6 route add ... nexthop ... nexthop ...) uses
fib6_siblings.  External nexthop (ip -6 route add ... nhid N) uses
nh_list, linked into &nh->f6i_list.

nft_fib6_info_nh_uses_dev() blindly walks &rt->fib6_siblings, causing
an OOB read past the struct nexthop slab when rt->nh is set:

  ==================================================================
  BUG: KASAN: slab-out-of-bounds in nft_fib6_eval+0x1362/0x16c0
  Read of size 8 at addr ffff888103a099d0 by task ping/386

  CPU: 2 UID: 0 PID: 386 Comm: ping Not tainted 7.1.0-rc3+ #251 PREEMPT
  Call Trace:
   
   dump_stack_lvl+0x76/0xa0
   print_report+0xd1/0x5f0
   kasan_report+0xe7/0x130
   __asan_report_load8_noabort+0x14/0x30
   nft_fib6_eval+0x1362/0x16c0
   nft_do_chain+0x279/0x18c0
   nft_do_chain_ipv6+0x1a8/0x230
   nf_hook_slow+0xad/0x200
   ipv6_rcv+0x152/0x380
   __netif_receive_skb_one_core+0x118/0x1c0
  ==================================================================

Branch by route shape: when rt->nh is set, walk via
nexthop_for_each_fib6_nh() (also covers nh groups, which the original
code missed); otherwise walk fib6_siblings, guarded by READ_ONCE() of
rt->fib6_nsiblings as required by commit 31d7d67ba127 ("ipv6: annotate
data-races around rt->fib6_nsiblings").

Fixes: 1c32b24c234b ("netfilter: nft_fib_ipv6: switch to fib6_lookup")
Signed-off-by: Jiayuan Chen 
Signed-off-by: Florian Westphal

netfilter: nft_fib_ipv6: walk fib6_siblings under RCU

2026-05-22T10:28:46+00:00

nft_fib6_info_nh_uses_dev() runs from nft_fib6_eval() in softirq under
rcu_read_lock().  fib6_siblings is modified by writers that hold
tb6_lock but do not wait for RCU readers, so the sibling walk should
use list_for_each_entry_rcu(): it adds READ_ONCE() on the ->next
pointer and lets CONFIG_PROVE_RCU_LIST validate the locking.

No functional change for non-debug builds.

Fixes: 1c32b24c234b ("netfilter: nft_fib_ipv6: switch to fib6_lookup")
Signed-off-by: Jiayuan Chen 
Signed-off-by: Florian Westphal

netfilter: ip6t_hbh: reject oversized option lists

2026-05-16T11:21:41+00:00

struct ip6t_opts stores at most IP6T_OPTS_OPTSNR option descriptors,
but hbh_mt6_check() does not reject larger optsnr values supplied from
userspace.

Validate optsnr in the rule setup path so only match data that fits the
fixed-size opts array can be installed. This follows the existing xtables
pattern of rejecting invalid user-provided counts in checkentry() and
keeps the packet matching path unchanged.

`struct ip6t_opts` has a fixed `opts[IP6T_OPTS_OPTSNR]` array,
where `IP6T_OPTS_OPTSNR` is 16, then off-by-one array access is possible:

[  137.924693][ T8692] UBSAN: array-index-out-of-bounds in ../net/ipv6/netfilter/ip6t_hbh.c:110:29
[  137.926167][ T8692] index 16 is out of range for type '__u16 [16]'

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@kernel.org
Reported-by: Yuan Tan 
Reported-by: Yifan Wu 
Reported-by: Juefei Pu 
Reported-by: Xin Liu 
Signed-off-by: Zhengchuan Liang 
Signed-off-by: Ren Wei 
Signed-off-by: Pablo Neira Ayuso

netfilter: x_tables: close dangling table module init race

2026-05-07T23:30:17+00:00

Similar to the previous ebtables patch:
template add exposes the table to userspace, we must do this last to
rnsure the pernet ops are set up (contain the destructors).

Fixes: fdacd57c79b7 ("netfilter: x_tables: never register tables by default")
Signed-off-by: Florian Westphal 
Signed-off-by: Pablo Neira Ayuso

netfilter: x_tables: add and use xtables_unregister_table_exit

2026-05-07T23:30:16+00:00

Previous change added xtables_unregister_table_pre_exit to detach the
table from the packetpath and to unlink it from the active table list.
In case of rmmod, userspace that is doing set/getsockopt for this table
will not be able to re-instantiate the table:
 1. The larval table has been removed already
 2. existing instantiated table is no longer on the xt pernet table list.

This adds the second stage helper:

unlink the table from the dying list, free the hook ops (if any) and do
the audit notification.  It replaces xt_unregister_table().

Fixes: fdacd57c79b7 ("netfilter: x_tables: never register tables by default")
Reported-by: Tristan Madani 
Reviewed-by: Tristan Madani 
Closes: https://lore.kernel.org/netfilter-devel/20260429175613.1459342-1-tristmd@gmail.com/
Signed-off-by: Florian Westphal 
Signed-off-by: Pablo Neira Ayuso

netfilter: x_tables: unregister the templates first

2026-05-07T23:30:16+00:00

When the module is going away we need to zap the template
first.  Else there is a small race window where userspace
could instantiate a new table after the pernet exit function
has removed the current table.

Fixes: fdacd57c79b7 ("netfilter: x_tables: never register tables by default")
Reported-by: Tristan Madani 
Reviewed-by: Tristan Madani 
Closes: https://lore.kernel.org/netfilter-devel/20260429175613.1459342-1-tristmd@gmail.com/
Signed-off-by: Florian Westphal 
Signed-off-by: Pablo Neira Ayuso

netfilter: x_tables: add and use xt_unregister_table_pre_exit

2026-05-07T23:30:16+00:00

Remove the copypasted variants of _pre_exit and add one single
function in the xtables core.  ebtables is not compatible with
x_tables and therefore unchanged.

This is a preparation patch to reduce noise in the followup
bug fixes.

Reviewed-by: Tristan Madani 
Signed-off-by: Florian Westphal 
Signed-off-by: Pablo Neira Ayuso

netfilter: x_tables: allocate hook ops while under mutex

2026-05-07T23:30:16+00:00

arp/ip(6)t_register_table() add the table to the per-netns list via
xt_register_table() before allocating the per-netns hook ops copy
via kmemdup_array().  This leaves a window where the table is
visible in the list with ops=NULL.

If the pernet exit happens runs concurrently the pre_exit callback finds
the table via xt_find_table() and passes the NULL ops pointer to
nf_unregister_net_hooks(), causing a NULL dereference:

  general protection fault in nf_unregister_net_hooks+0xbc/0x150
  RIP: nf_unregister_net_hooks (net/netfilter/core.c:613)
  Call Trace:
    ipt_unregister_table_pre_exit
    iptable_mangle_net_pre_exit
    ops_pre_exit_list
    cleanup_net

Fix by moving the ops allocation into the xtables core so the table is
never in the list without valid ops.  Also ensure the table is no longer
processing packets before its torn down on error unwind.
nf_register_net_hooks might have published at least one hook; call
synchronize_rcu() if there was an error.

audit log register message gets deferred until all operations have
passed, this avoids need to emit another ureg message in case of
error unwinding.

Based on earlier patch by Tristan Madani.

Fixes: f9006acc8dfe5 ("netfilter: arp_tables: pass table pointer via nf_hook_ops")
Fixes: ee177a54413a ("netfilter: ip6_tables: pass table pointer via nf_hook_ops")
Fixes: ae689334225f ("netfilter: ip_tables: pass table pointer via nf_hook_ops")
Link: https://lore.kernel.org/netfilter-devel/20260429175613.1459342-1-tristmd@gmail.com/
Signed-off-by: Tristan Madani 
Signed-off-by: Florian Westphal 
Signed-off-by: Pablo Neira Ayuso

netfilter: nf_socket: skip socket lookup for non-first fragments

2026-04-30T15:59:01+00:00

Both nft_socket and xt_socket relies on L4 headers to perform socket
lookup in the slow path. For fragmented packets, while the IP protocol
remains constant across all fragments, only the first fragment contains
the actual L4 header.

As the expression/match could be attached to a chain with a priority
lower than -400, it could bypass defragmentation.

Add a check for fragmentation in the lookup functions directly so the
problem is handled for both nft_socket and xt_socket at the same time.
In addition, future users of the functions would not need to care about
this.

Fixes: 902d6a4c2a4f ("netfilter: nf_defrag: Skip defrag if NOTRACK is set")
Fixes: 554ced0a6e29 ("netfilter: nf_tables: add support for native socket matching")
Signed-off-by: Fernando Fernandez Mancera 
Signed-off-by: Pablo Neira Ayuso