Copyright © 2012 Red Hat, Inc. All rights reserved. Moderate 2026-06-25T00:00:00 kernel: ipv6: anycast: insert aca into global hash under idev->lock 7.0 CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H CWE-366

In the Linux kernel, the following vulnerability has been resolved: ipv6: anycast: insert aca into global hash under idev->lock syzbot reported a splat [1]: a slab-use-after-free in ipv6_chk_acast_addr(), which walks the global inet6_acaddr_lst[] hash under RCU and dereferences a struct ifacaddr6 that has already been freed while still linked in the hash, so a later reader walks into a dangling node. In __ipv6_dev_ac_inc() the aca is allocated with refcount 1, then aca_get() bumps it to 2 to keep it alive across the unlocked region. It is published to idev->ac_list under idev->lock, but ipv6_add_acaddr_hash() runs after write_unlock_bh(). A concurrent teardown (ipv6_ac_destroy_dev() from addrconf_ifdown(), under RTNL) can slip into that window: CPU0 __ipv6_dev_ac_inc CPU1 ipv6_ac_destroy_dev (RTNL) ------------------------------ ------------------------------------ aca_alloc() refcnt 1 aca_get() refcnt 2 write_lock_bh(idev->lock) add aca to ac_list write_unlock_bh(idev->lock) write_lock_bh(idev->lock) pull aca off ac_list write_unlock_bh(idev->lock) ipv6_del_acaddr_hash(aca) hlist_del_init_rcu() is a no-op, aca is not in the hash yet aca_put() refcnt 2->1 ipv6_add_acaddr_hash(aca) aca now inserted into the hash aca_put() refcnt 1->0 call_rcu(aca_free_rcu) -> kfree(aca) The hash removal becomes a no-op because the insertion has not happened yet, so once CPU0 inserts and drops the last reference, the aca is freed while still linked in inet6_acaddr_lst[], and readers dereference freed memory after the slab slot is reused. This window opened once RTNL stopped serializing the join path against device teardown. Move ipv6_add_acaddr_hash() inside the idev->lock section so the ac_list and hash insertions are atomic with respect to teardown: a racing remover now either misses the aca entirely or finds it in both lists. acaddr_hash_lock is now nested under idev->lock, which is acquired in softirq context, so switch all acaddr_hash_lock sites to spin_lock_bh() to avoid the irq lock inversion reported in [2]. [1] https://syzkaller.appspot.com/bug?extid=a01df04303c131efbf3a [2] https://lore.kernel.org/netdev/6a194ef7.ba3b1513.1890b4.0000.GAE@google.com/

A flaw was found in the Linux kernel, specifically within its management of IPv6 anycast addresses. A timing issue, known as a race condition, can occur when these addresses are added and removed from a system's internal list. This can lead to the system attempting to access memory that has already been released, a condition known as a use-after-free. Such an issue could potentially cause system instability or a denial of service (DoS), making the system unavailable to users.

Red Hat Enterprise Linux 10 Affected kernel Red Hat Enterprise Linux 6 Not affected kernel Red Hat Enterprise Linux 7 Not affected kernel Red Hat Enterprise Linux 7 Not affected kernel-rt Red Hat Enterprise Linux 8 Not affected kernel Red Hat Enterprise Linux 8 Not affected kernel-rt Red Hat Enterprise Linux 9 Not affected kernel Red Hat Enterprise Linux 9 Not affected kernel-rt https://www.cve.org/CVERecord?id=CVE-2026-53259 https://nvd.nist.gov/vuln/detail/CVE-2026-53259 https://lore.kernel.org/linux-cve-announce/2026062515-CVE-2026-53259-5758@gregkh/T