CVE-2026-74630: ipv6: prevent in6_dev_get() from resurrecting inet6_dev

From: Greg Kroah-Hartman <[email protected]>

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

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

ipv6: prevent in6_dev_get() from resurrecting inet6_dev

in6_dev_get() reads dev->ip6_ptr under RCU and then unconditionally
increments its refcount. Device teardown can clear the pointer and drop
the last reference between these operations. The increment then
resurrects an object whose RCU free has already been queued, so callers
can use it after it is freed.

Use refcount_inc_not_zero() and return NULL when the object has already
reached zero. RCU keeps the memory accessible through the attempted
reference acquisition, and a successful increment pins the object for
the caller.

An independent run on the exact unpatched 6f5156d7a31a (v7.2-rc3)
kernel reproduced the invalid reference acquisition as UID 1000:

  refcount_t: addition on 0; use-after-free.
  ip6_mc_source+0xef4/0x17e0

It was followed by the corresponding reference underflow in
ip6_mc_source(). The supplied trace from the same unpatched revision
additionally shows the access after the RCU read-side section ends:

  BUG: KASAN: slab-use-after-free in mutex_lock+0x76/0xe0
  Write of size 8 at addr ffff888015b50240 by task poc/1219

Bug found and triaged by OpenAI Security Research and
validated by Trail of Bits.

The Linux kernel CVE team has assigned CVE-2026-74630 to this issue.


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

	Issue introduced in 2.6.19 with commit 8814c4b533817df825485ff32ce6ac406c3a54d1 and fixed in 5.10.265 with commit 785d908f8d21c8bc78b6fb2c2932ab662bf6918a
	Issue introduced in 2.6.19 with commit 8814c4b533817df825485ff32ce6ac406c3a54d1 and fixed in 5.15.216 with commit aedcfefdb5b7ed7f8a6196a3e68a25bdbe51d2f8
	Issue introduced in 2.6.19 with commit 8814c4b533817df825485ff32ce6ac406c3a54d1 and fixed in 6.1.183 with commit 145812b678de9f3b59780173be3c0d22ed60dd93
	Issue introduced in 2.6.19 with commit 8814c4b533817df825485ff32ce6ac406c3a54d1 and fixed in 6.6.152 with commit cc5bd568f9b7683e60841b6fd02c10d64535bd6e
	Issue introduced in 2.6.19 with commit 8814c4b533817df825485ff32ce6ac406c3a54d1 and fixed in 6.12.104 with commit 1c206d461c680c3151daa3c89fc26eaf5bf98a7f
	Issue introduced in 2.6.19 with commit 8814c4b533817df825485ff32ce6ac406c3a54d1 and fixed in 6.18.45 with commit 680fbd7942185448eadb990a3d10a53eb946b702
	Issue introduced in 2.6.19 with commit 8814c4b533817df825485ff32ce6ac406c3a54d1 and fixed in 7.1.9 with commit 14e812ab41df0cac033479da835ec9a5de633404
	Issue introduced in 2.6.19 with commit 8814c4b533817df825485ff32ce6ac406c3a54d1 and fixed in 7.2 with commit 0e243671bc7b8eaf00f83dd2f4367436dc0cff98

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-2026-74630
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:
	include/net/addrconf.h


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/785d908f8d21c8bc78b6fb2c2932ab662bf6918a
	https://git.kernel.org/stable/c/aedcfefdb5b7ed7f8a6196a3e68a25bdbe51d2f8
	https://git.kernel.org/stable/c/145812b678de9f3b59780173be3c0d22ed60dd93
	https://git.kernel.org/stable/c/cc5bd568f9b7683e60841b6fd02c10d64535bd6e
	https://git.kernel.org/stable/c/1c206d461c680c3151daa3c89fc26eaf5bf98a7f
	https://git.kernel.org/stable/c/680fbd7942185448eadb990a3d10a53eb946b702
	https://git.kernel.org/stable/c/14e812ab41df0cac033479da835ec9a5de633404
	https://git.kernel.org/stable/c/0e243671bc7b8eaf00f83dd2f4367436dc0cff98