CVE-2026-46116xfrm: defensively unhash xfrm_state lists in __xfrm_state_delete

Official description

In the Linux kernel, the following vulnerability has been resolved: xfrm: defensively unhash xfrm_state lists in __xfrm_state_delete KASAN reproduces a slab-use-after-free in __xfrm_state_delete()'s hlist_del_rcu calls under syzkaller load on linux-6.12.y stable (reproduced on 6.12.47, also reachable via the same code path on torvalds/master and on the ipsec tree). Nine unique signatures cluster in the xfrm_state lifecycle, the load-bearing one being: BUG: KASAN: slab-use-after-free in __hlist_del include/linux/list.h:990 [inline] BUG: KASAN: slab-use-after-free in hlist_del_rcu include/linux/rculist.h:516 [inline] BUG: KASAN: slab-use-after-free in __xfrm_state_delete net/xfrm/xfrm_state.c Write of size 8 at addr ffff8881198bcb70 by task kworker/u8:9/435 Workqueue: netns cleanup_net Call Trace: __hlist_del / hlist_del_rcu __xfrm_state_delete xfrm_state_delete xfrm_state_flush xfrm_state_fini ops_exit_list cleanup_net The other observed signatures hit the same slab object from __xfrm_state_lookup, xfrm_alloc_spi, __xfrm_state_insert and an OOB write variant of __xfrm_state_delete, all on the byseq/byspi hash chains. __xfrm_state_delete() guards its byseq and byspi unhashes with value-based predicates: if (x->km.seq) hlist_del_rcu(&x->byseq); if (x->id.spi) hlist_del_rcu(&x->byspi); while everywhere else in the file (e.g. state_cache, state_cache_input) the safer hlist_unhashed() check is used. xfrm_alloc_spi() sets x->id.spi = newspi inside xfrm_state_lock and then immediately inserts into byspi, but a path that observes x->id.spi != 0 outside of xfrm_state_lock can still skip-or-hit the byspi unhash inconsistently with whether x is actually on the list. The same holds for x->km.seq versus byseq, and the bydst/bysrc unhashes have no predicate at all, so a second __xfrm_state_delete() on the same object writes through LIST_POISON pprev. The defensive change here: - Use hlist_del_init_rcu() instead of hlist_del_rcu() on bydst, bysrc, byseq and byspi so a second deletion is a no-op rather than a write through LIST_POISON pprev. The byseq/byspi nodes are already initialised in xfrm_state_alloc(). - Test hlist_unhashed() rather than the value predicate for byseq/byspi, so the unhash decision tracks list state rather than mutable scalar fields. Empirical verification: applied this patch on top of v6.12.47, rebuilt, and re-ran the same syzkaller harness for 1h16m on a previously-crashy configuration that produced ~100 hits each of slab-use-after-free Read in xfrm_alloc_spi / Read in __xfrm_state_lookup / Write in __xfrm_state_delete. After the patch, 7.1M execs across 32 VMs at ~1550 exec/sec produced zero xfrm_state UAF/OOB hits. /proc/slabinfo confirms the xfrm_state slab is actively allocated and freed during the run (~143 KiB resident), so the fuzzer is still exercising those code paths -- they just no longer crash. Reproduction: - Linux 6.12.47 x86_64 + KASAN_GENERIC + KASAN_INLINE + KCOV - syzkaller @ 746545b8b1e4c3a128db8652b340d3df90ce61db - 32 QEMU/KVM VMs x 2 vCPU on AWS c5.metal bare metal - 9 unique signatures collected in ~9h, all within xfrm_state lifecycle

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/6b4dc3181b4bfc5f5fc33ab33b1dc6e15759f4b6
• https://git.kernel.org/stable/c/3943fcad7694a7d0b15aeabe7d3cc2a2eb8e92e8
• https://git.kernel.org/stable/c/2c617848ae6e4f07a3e397f604208c293bbecacc
• https://git.kernel.org/stable/c/b4a53add2fa8f1b5aa17d4c5686c320785fab182
• https://git.kernel.org/stable/c/26edb0a3c99f9d958c212be68b21f1221614dcf0
• https://git.kernel.org/stable/c/4980162de555cb838f1a189ce7d2cbf5d2e7b050
• https://git.kernel.org/stable/c/a2e2d08fb070fab4947447171f1c4e3ca5a188e5
• https://git.kernel.org/stable/c/14acf9652e5690de3c7486c6db5fb8dafd0a32a3
• https://access.redhat.com/security/cve/CVE-2026-46116 vdb-entry, x_refsource_REDHAT
• RHBZ#2482523 issue-tracking, x_refsource_REDHAT
• https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-46116.json x_sadp-csaf-vex
• https://access.redhat.com/errata/RHSA-2026:41235 vendor-advisory, x_refsource_REDHAT
• https://access.redhat.com/errata/RHSA-2026:41234 vendor-advisory, x_refsource_REDHAT
• https://access.redhat.com/errata/RHSA-2026:39371 vendor-advisory, x_refsource_REDHAT
• https://access.redhat.com/errata/RHSA-2026:42919 vendor-advisory, x_refsource_REDHAT
• https://access.redhat.com/errata/RHSA-2026:47739 vendor-advisory, x_refsource_REDHAT
• https://access.redhat.com/errata/RHSA-2026:43231 vendor-advisory, x_refsource_REDHAT
• https://access.redhat.com/errata/RHSA-2026:44385 vendor-advisory, x_refsource_REDHAT
• https://access.redhat.com/errata/RHSA-2026:36018 vendor-advisory, x_refsource_REDHAT
• https://access.redhat.com/errata/RHSA-2026:59143 vendor-advisory, x_refsource_REDHAT
• https://access.redhat.com/errata/RHSA-2026:39179 vendor-advisory, x_refsource_REDHAT
• https://access.redhat.com/errata/RHSA-2026:59146 vendor-advisory, x_refsource_REDHAT
• https://access.redhat.com/errata/RHSA-2026:47633 vendor-advisory, x_refsource_REDHAT
• https://access.redhat.com/errata/RHSA-2026:49033 vendor-advisory, x_refsource_REDHAT
• https://access.redhat.com/errata/RHSA-2026:47869 vendor-advisory, x_refsource_REDHAT
• https://access.redhat.com/errata/RHSA-2026:59142 vendor-advisory, x_refsource_REDHAT
• https://access.redhat.com/errata/RHSA-2026:59147 vendor-advisory, x_refsource_REDHAT
• https://access.redhat.com/errata/RHSA-2026:59145 vendor-advisory, x_refsource_REDHAT
• https://access.redhat.com/errata/RHSA-2026:59148 vendor-advisory, x_refsource_REDHAT
• https://access.redhat.com/errata/RHSA-2026:59149 vendor-advisory, x_refsource_REDHAT
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• https://access.redhat.com/errata/RHSA-2026:47632 vendor-advisory, x_refsource_REDHAT
• https://cert-portal.siemens.com/productcert/html/ssa-019113.html
• https://cert-portal.siemens.com/productcert/html/ssa-457936.html
• https://cert-portal.siemens.com/productcert/html/ssa-784472.html