CVE-2025-39894

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

netfilter: br_netfilter: do not check confirmed bit in br_nf_local_in() after confirm

When send a broadcast packet to a tap device, which was added to a bridge,
br_nf_local_in() is called to confirm the conntrack. If another conntrack
with the same hash value is added to the hash table, which can be
triggered by a normal packet to a non-bridge device, the below warning
may happen.

------------[ cut here ]------------
WARNING: CPU: 1 PID: 96 at net/bridge/br_netfilter_hooks.c:632 br_nf_local_in+0x168/0x200
CPU: 1 UID: 0 PID: 96 Comm: tap_send Not tainted 6.17.0-rc2-dirty #44 PREEMPT(voluntary)
RIP: 0010:br_nf_local_in+0x168/0x200
Call Trace:
<TASK>
nf_hook_slow+0x3e/0xf0
br_pass_frame_up+0x103/0x180
br_handle_frame_finish+0x2de/0x5b0
br_nf_hook_thresh+0xc0/0x120
br_nf_pre_routing_finish+0x168/0x3a0
br_nf_pre_routing+0x237/0x5e0
br_handle_frame+0x1ec/0x3c0
__netif_receive_skb_core+0x225/0x1210
__netif_receive_skb_one_core+0x37/0xa0
netif_receive_skb+0x36/0x160
tun_get_user+0xa54/0x10c0
tun_chr_write_iter+0x65/0xb0
vfs_write+0x305/0x410
ksys_write+0x60/0xd0
do_syscall_64+0xa4/0x260
entry_SYSCALL_64_after_hwframe+0x77/0x7f
</TASK>
---[ end trace 0000000000000000 ]---

To solve the hash conflict, nf_ct_resolve_clash() try to merge the
conntracks, and update skb->_nfct. However, br_nf_local_in() still use the
old ct from local variable 'nfct' after confirm(), which leads to this
warning.

If confirm() does not insert the conntrack entry and return NF_DROP, the
warning may also occur. There is no need to reserve the WARN_ON_ONCE, just
remove it.

• https://git.kernel.org/stable/c/479a54ab92087318514c82428a87af2d7af1a576

  416baaa9-dc9f-4396-8d5f-8c081fb06d67 Patch
• https://git.kernel.org/stable/c/50db11e2bbb635e38e3dd096215580d6adb41fb0

  416baaa9-dc9f-4396-8d5f-8c081fb06d67 Patch
• https://git.kernel.org/stable/c/a74abcf0f09f59daeecf7a3ba9c1d690808b0afe

  416baaa9-dc9f-4396-8d5f-8c081fb06d67 Patch
• https://git.kernel.org/stable/c/c47ca77fee9071aa543bae592dd2a384f895c8b6

  416baaa9-dc9f-4396-8d5f-8c081fb06d67 Patch
• https://git.kernel.org/stable/c/ccbad4803225eafe0175d3cb19f0d8d73b504a94

  416baaa9-dc9f-4396-8d5f-8c081fb06d67 Patch
• https://git.kernel.org/stable/c/d00c8b0daf56012f69075e3377da67878c775e4c

  416baaa9-dc9f-4396-8d5f-8c081fb06d67 Patch
• https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html

  af854a3a-2127-422b-91ae-364da2661108 Third Party Advisory