linux.git/net/ipv6/netfilter, branch v7.1

netfilter: nft_fib: fix stale stack leak via the OIFNAME register

2026-06-10T16:00:19+00:00

For NFT_FIB_RESULT_OIFNAME the destination register is declared with
len = IFNAMSIZ (four 32-bit registers), but on the lookup-fail,
RTN_LOCAL and oif-mismatch paths nft_fib{4,6}_eval() only writes one
register via "*dest = 0". The remaining three registers are left as
whatever was on the stack in nft_do_chain()'s struct nft_regs, and a
downstream expression that loads the register span can leak that
uninitialised kernel stack to userspace.

The NFTA_FIB_F_PRESENT existence check has the same shape: it is only
meaningful for NFT_FIB_RESULT_OIF, yet it was accepted for any result type
while the eval stores a single byte via nft_reg_store8(), leaving the rest
of the declared span stale.

Fix both:

 - replace the bare "*dest = 0" in the eval with nft_fib_store_result(),
   which strscpy_pad()s the whole IFNAMSIZ for OIFNAME (and is already
   used on the other early-return path), and

 - restrict NFTA_FIB_F_PRESENT to NFT_FIB_RESULT_OIF and declare its
   destination as a single u8, so the marked span matches the one byte
   the eval writes.

Fixes: f6d0cbcf09c5 ("netfilter: nf_tables: add fib expression")
Suggested-by: Florian Westphal 
Cc: stable@vger.kernel.org
Signed-off-by: Davide Ornaghi 
Signed-off-by: Pablo Neira Ayuso

netfilter: x_tables: avoid leaking percpu counter pointers

2026-06-10T15:59:01+00:00

The native and compat get-entries paths copy the fixed rule entry header
from the kernelized rule blob to userspace before overwriting the entry's
counter fields with a sanitized counter snapshot.

On SMP kernels, entry->counters.pcnt contains the percpu allocation
address used by x_tables rule counters. A caller can provide a userspace
buffer that faults during the initial fixed-header copy after pcnt has
been copied but before the later sanitized counter copy runs. The syscall
then returns -EFAULT while leaving the raw percpu pointer in userspace.

Copy only the fixed entry prefix before counters from the kernelized rule
blob, then copy the sanitized counter snapshot into the counter field.
Apply this ordering to the IPv4, IPv6, and ARP native and compat
get-entries implementations so a fault cannot expose the internal percpu
counter pointer.

Fixes: 71ae0dff02d7 ("netfilter: xtables: use percpu rule counters")
Signed-off-by: Kyle Zeng 
Signed-off-by: Pablo Neira Ayuso

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