linux-cve-announce - CVE-2025-38638: ipv6: add a retry logic in net6_rt

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Message-ID: <2025082234-CVE-2025-38638-caad@gregkh>
Date: Fri, 22 Aug 2025 18:00:46 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-38638: ipv6: add a retry logic in net6_rt_notify()

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

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

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

ipv6: add a retry logic in net6_rt_notify()

inet6_rt_notify() can be called under RCU protection only.
This means the route could be changed concurrently
and rt6_fill_node() could return -EMSGSIZE.

Re-size the skb when this happens and retry, removing
one WARN_ON() that syzbot was able to trigger:

WARNING: CPU: 3 PID: 6291 at net/ipv6/route.c:6342 inet6_rt_notify+0x475/0x4b0 net/ipv6/route.c:6342
Modules linked in:
CPU: 3 UID: 0 PID: 6291 Comm: syz.0.77 Not tainted 6.16.0-rc7-syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
 RIP: 0010:inet6_rt_notify+0x475/0x4b0 net/ipv6/route.c:6342
Code: fc ff ff e8 6d 52 ea f7 e9 47 fc ff ff 48 8b 7c 24 08 4c 89 04 24 e8 5a 52 ea f7 4c 8b 04 24 e9 94 fd ff ff e8 9c fe 84 f7 90 <0f> 0b 90 e9 bd fd ff ff e8 6e 52 ea f7 e9 bb fb ff ff 48 89 df e8
RSP: 0018:ffffc900035cf1d8 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffffc900035cf540 RCX: ffffffff8a36e790
RDX: ffff88802f7e8000 RSI: ffffffff8a36e9d4 RDI: 0000000000000005
RBP: ffff88803c230f00 R08: 0000000000000005 R09: 00000000ffffffa6
R10: 00000000ffffffa6 R11: 0000000000000001 R12: 00000000ffffffa6
R13: 0000000000000900 R14: ffff888032ea4100 R15: 0000000000000000
FS:  00007fac7b89a6c0(0000) GS:ffff8880d6a20000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fac7b899f98 CR3: 0000000034b3f000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
  ip6_route_mpath_notify+0xde/0x280 net/ipv6/route.c:5356
  ip6_route_multipath_add+0x1181/0x1bd0 net/ipv6/route.c:5536
  inet6_rtm_newroute+0xe4/0x1a0 net/ipv6/route.c:5647
  rtnetlink_rcv_msg+0x95e/0xe90 net/core/rtnetlink.c:6944
  netlink_rcv_skb+0x155/0x420 net/netlink/af_netlink.c:2552
  netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
  netlink_unicast+0x58d/0x850 net/netlink/af_netlink.c:1346
  netlink_sendmsg+0x8d1/0xdd0 net/netlink/af_netlink.c:1896
  sock_sendmsg_nosec net/socket.c:712 [inline]
  __sock_sendmsg net/socket.c:727 [inline]
  ____sys_sendmsg+0xa95/0xc70 net/socket.c:2566
  ___sys_sendmsg+0x134/0x1d0 net/socket.c:2620

The Linux kernel CVE team has assigned CVE-2025-38638 to this issue.


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

	Issue introduced in 6.16 with commit 169fd62799e8acabbfb4760799be11138ced949c and fixed in 6.16.1 with commit 0bdca3439a22c70eb8f404acd61bf7aca5d731b0
	Issue introduced in 6.16 with commit 169fd62799e8acabbfb4760799be11138ced949c and fixed in 6.17-rc1 with commit ea2f921db7a483a526058c5b5b8162edd88dabe5

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-2025-38638
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/ipv6/route.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/0bdca3439a22c70eb8f404acd61bf7aca5d731b0
	https://git.kernel.org/stable/c/ea2f921db7a483a526058c5b5b8162edd88dabe5