linux-cve-announce - CVE-2025-38589: neighbour: Fix null-ptr-deref in neigh_flush

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Message-ID: <2025081916-CVE-2025-38589-52ae@gregkh>
Date: Tue, 19 Aug 2025 19:18:35 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-38589: neighbour: Fix null-ptr-deref in neigh_flush_dev().

From: Greg Kroah-Hartman <gregkh@...nel.org>

Description
===========

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

neighbour: Fix null-ptr-deref in neigh_flush_dev().

kernel test robot reported null-ptr-deref in neigh_flush_dev(). [0]

The cited commit introduced per-netdev neighbour list and converted
neigh_flush_dev() to use it instead of the global hash table.

One thing we missed is that neigh_table_clear() calls neigh_ifdown()
with NULL dev.

Let's restore the hash table iteration.

Note that IPv6 module is no longer unloadable, so neigh_table_clear()
is called only when IPv6 fails to initialise, which is unlikely to
happen.

[0]:
IPv6: Attempt to unregister permanent protocol 136
IPv6: Attempt to unregister permanent protocol 17
Oops: general protection fault, probably for non-canonical address 0xdffffc00000001a0: 0000 [#1] SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000d00-0x0000000000000d07]
CPU: 1 UID: 0 PID: 1 Comm: systemd Tainted: G                T  6.12.0-rc6-01246-gf7f52738637f #1
Tainted: [T]=RANDSTRUCT
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:neigh_flush_dev.llvm.6395807810224103582+0x52/0x570
Code: c1 e8 03 42 8a 04 38 84 c0 0f 85 15 05 00 00 31 c0 41 83 3e 0a 0f 94 c0 48 8d 1c c3 48 81 c3 f8 0c 00 00 48 89 d8 48 c1 e8 03 <42> 80 3c 38 00 74 08 48 89 df e8 f7 49 93 fe 4c 8b 3b 4d 85 ff 0f
RSP: 0000:ffff88810026f408 EFLAGS: 00010206
RAX: 00000000000001a0 RBX: 0000000000000d00 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffffc0631640
RBP: ffff88810026f470 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: ffffffffc0625250 R14: ffffffffc0631640 R15: dffffc0000000000
FS:  00007f575cb83940(0000) GS:ffff8883aee00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f575db40008 CR3: 00000002bf936000 CR4: 00000000000406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 __neigh_ifdown.llvm.6395807810224103582+0x44/0x390
 neigh_table_clear+0xb1/0x268
 ndisc_cleanup+0x21/0x38 [ipv6]
 init_module+0x2f5/0x468 [ipv6]
 do_one_initcall+0x1ba/0x628
 do_init_module+0x21a/0x530
 load_module+0x2550/0x2ea0
 __se_sys_finit_module+0x3d2/0x620
 __x64_sys_finit_module+0x76/0x88
 x64_sys_call+0x7ff/0xde8
 do_syscall_64+0xfb/0x1e8
 entry_SYSCALL_64_after_hwframe+0x67/0x6f
RIP: 0033:0x7f575d6f2719
Code: 08 89 e8 5b 5d c3 66 2e 0f 1f 84 00 00 00 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d b7 06 0d 00 f7 d8 64 89 01 48
RSP: 002b:00007fff82a2a268 EFLAGS: 00000246 ORIG_RAX: 0000000000000139
RAX: ffffffffffffffda RBX: 0000557827b45310 RCX: 00007f575d6f2719
RDX: 0000000000000000 RSI: 00007f575d584efd RDI: 0000000000000004
RBP: 00007f575d584efd R08: 0000000000000000 R09: 0000557827b47b00
R10: 0000000000000004 R11: 0000000000000246 R12: 0000000000020000
R13: 0000000000000000 R14: 0000557827b470e0 R15: 00007f575dbb4270
 </TASK>
Modules linked in: ipv6(+)

The Linux kernel CVE team has assigned CVE-2025-38589 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.13 with commit f7f52738637f4361c108cad36e23ee98959a9006 and fixed in 6.15.10 with commit d9c4328795697ebc392a63fece3901999c09cddd
	Issue introduced in 6.13 with commit f7f52738637f4361c108cad36e23ee98959a9006 and fixed in 6.16.1 with commit 47fbd7f8df19bdfbe334ee83f35568c9a29221ae
	Issue introduced in 6.13 with commit f7f52738637f4361c108cad36e23ee98959a9006 and fixed in 6.17-rc1 with commit 1bbb76a899486827394530916f01214d049931b3

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-38589
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	net/core/neighbour.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/d9c4328795697ebc392a63fece3901999c09cddd
	https://git.kernel.org/stable/c/47fbd7f8df19bdfbe334ee83f35568c9a29221ae
	https://git.kernel.org/stable/c/1bbb76a899486827394530916f01214d049931b3