CVE-2026-46116
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
AI Insight
LLM-synthesized narrative grounded in this CVE's description and references.
A use-after-free vulnerability in Linux kernel's xfrm subsystem allows race conditions during state deletion, leading to memory corruption.
Vulnerability
In the Linux kernel, a slab-use-after-free vulnerability exists in the xfrm subsystem's __xfrm_state_delete() function, as reported in CVE-2026-46116. The issue affects versions up to and including 6.12.47, and is also reachable on torvalds/master and the ipsec tree. The root cause is that the function uses value-based predicates (x->km.seq and x->id.spi) to guard hash list deletions via hlist_del_rcu(), while other parts of the code use the safer hlist_unhashed() check. This inconsistency allows a race condition where an object may be deleted twice or accessed after freeing, specifically on the byseq and byspi hash chains [1].
Exploitation
An attacker would need local access to trigger the race condition, typically via a crafted workload such as those generated by syzkaller. The exploitation requires the attacker to manipulate the xfrm state lifecycle, causing a second __xfrm_state_delete() to occur on the same object while it is already being deleted. This race can be triggered during network namespace cleanup (cleanup_net workqueue), where multiple threads may attempt to delete xfrm states concurrently [1].
Impact
Successful exploitation leads to a use-after-free condition, resulting in memory corruption that can manifest as a kernel panic, denial of service, or potentially arbitrary code execution with kernel privileges. The CVSS score is not provided, but given the nature of use-after-free in kernel memory, the impact is severe and could allow an attacker to compromise the entire system.
Mitigation
The fix is implemented by git commit 4980162de555cb838f1a189ce7d2cbf5d2e7b050, which replaces hlist_del_rcu() with hlist_del_init_rcu() for the bydst, bysrc, byseq, and byspi hash chains in __xfrm_state_delete(). This defensive change ensures that a second deletion attempt is safe. Users should apply this patch or update to a kernel version containing it. The commit is backported to the stable kernel branches where the vulnerability is present [1].
AI Insight generated on May 28, 2026. Synthesized from this CVE's description and the cited reference URLs; citations are validated against the source bundle.
Affected products
1Patches
10b4a53add2fa8xfrm: defensively unhash xfrm_state lists in __xfrm_state_delete
2 files changed · +12 −14
net/xfrm/xfrm_state.c+6 −7 modifieddiff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c index ca42c9b8cecc3e..8ba31cf9b31993 100644 --- a/net/xfrm/xfrm_state.c +++ b/net/xfrm/xfrm_state.c @@ -752,12 +752,12 @@ int __xfrm_state_delete(struct xfrm_state *x) x->km.state = XFRM_STATE_DEAD; spin_lock(&net->xfrm.xfrm_state_lock); list_del(&x->km.all); - hlist_del_rcu(&x->bydst); - hlist_del_rcu(&x->bysrc); - if (x->km.seq) - hlist_del_rcu(&x->byseq); - if (x->id.spi) - hlist_del_rcu(&x->byspi); + hlist_del_init_rcu(&x->bydst); + hlist_del_init_rcu(&x->bysrc); + if (!hlist_unhashed(&x->byseq)) + hlist_del_init_rcu(&x->byseq); + if (!hlist_unhashed(&x->byspi)) + hlist_del_init_rcu(&x->byspi); net->xfrm.state_num--; spin_unlock(&net->xfrm.xfrm_state_lock); -- cgit 1.3-korg
net/xfrm/xfrm_state.c+6 −7 modifieddiff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c index ca42c9b8cecc3e..8ba31cf9b31993 100644 --- a/net/xfrm/xfrm_state.c +++ b/net/xfrm/xfrm_state.c @@ -752,12 +752,12 @@ int __xfrm_state_delete(struct xfrm_state *x) x->km.state = XFRM_STATE_DEAD; spin_lock(&net->xfrm.xfrm_state_lock); list_del(&x->km.all); - hlist_del_rcu(&x->bydst); - hlist_del_rcu(&x->bysrc); - if (x->km.seq) - hlist_del_rcu(&x->byseq); - if (x->id.spi) - hlist_del_rcu(&x->byspi); + hlist_del_init_rcu(&x->bydst); + hlist_del_init_rcu(&x->bysrc); + if (!hlist_unhashed(&x->byseq)) + hlist_del_init_rcu(&x->byseq); + if (!hlist_unhashed(&x->byspi)) + hlist_del_init_rcu(&x->byspi); net->xfrm.state_num--; spin_unlock(&net->xfrm.xfrm_state_lock); -- cgit 1.3-korg
26edb0a3c99fxfrm: defensively unhash xfrm_state lists in __xfrm_state_delete
2 files changed · +12 −14
net/xfrm/xfrm_state.c+6 −7 modifieddiff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c index a55c88b43c3394..6a92d88f9e0363 100644 --- a/net/xfrm/xfrm_state.c +++ b/net/xfrm/xfrm_state.c @@ -755,17 +755,17 @@ int __xfrm_state_delete(struct xfrm_state *x) spin_lock(&net->xfrm.xfrm_state_lock); list_del(&x->km.all); - hlist_del_rcu(&x->bydst); - hlist_del_rcu(&x->bysrc); - if (x->km.seq) - hlist_del_rcu(&x->byseq); + hlist_del_init_rcu(&x->bydst); + hlist_del_init_rcu(&x->bysrc); + if (!hlist_unhashed(&x->byseq)) + hlist_del_init_rcu(&x->byseq); if (!hlist_unhashed(&x->state_cache)) hlist_del_rcu(&x->state_cache); if (!hlist_unhashed(&x->state_cache_input)) hlist_del_rcu(&x->state_cache_input); - if (x->id.spi) - hlist_del_rcu(&x->byspi); + if (!hlist_unhashed(&x->byspi)) + hlist_del_init_rcu(&x->byspi); net->xfrm.state_num--; xfrm_nat_keepalive_state_updated(x); spin_unlock(&net->xfrm.xfrm_state_lock); -- cgit 1.3-korg
net/xfrm/xfrm_state.c+6 −7 modifieddiff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c index a55c88b43c3394..6a92d88f9e0363 100644 --- a/net/xfrm/xfrm_state.c +++ b/net/xfrm/xfrm_state.c @@ -755,17 +755,17 @@ int __xfrm_state_delete(struct xfrm_state *x) spin_lock(&net->xfrm.xfrm_state_lock); list_del(&x->km.all); - hlist_del_rcu(&x->bydst); - hlist_del_rcu(&x->bysrc); - if (x->km.seq) - hlist_del_rcu(&x->byseq); + hlist_del_init_rcu(&x->bydst); + hlist_del_init_rcu(&x->bysrc); + if (!hlist_unhashed(&x->byseq)) + hlist_del_init_rcu(&x->byseq); if (!hlist_unhashed(&x->state_cache)) hlist_del_rcu(&x->state_cache); if (!hlist_unhashed(&x->state_cache_input)) hlist_del_rcu(&x->state_cache_input); - if (x->id.spi) - hlist_del_rcu(&x->byspi); + if (!hlist_unhashed(&x->byspi)) + hlist_del_init_rcu(&x->byspi); net->xfrm.state_num--; xfrm_nat_keepalive_state_updated(x); spin_unlock(&net->xfrm.xfrm_state_lock); -- cgit 1.3-korg
a2e2d08fb070xfrm: defensively unhash xfrm_state lists in __xfrm_state_delete
2 files changed · +12 −14
net/xfrm/xfrm_state.c+6 −7 modifieddiff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c index 1748d374abcab3..686014d394298c 100644 --- a/net/xfrm/xfrm_state.c +++ b/net/xfrm/xfrm_state.c @@ -818,17 +818,17 @@ int __xfrm_state_delete(struct xfrm_state *x) spin_lock(&net->xfrm.xfrm_state_lock); list_del(&x->km.all); - hlist_del_rcu(&x->bydst); - hlist_del_rcu(&x->bysrc); - if (x->km.seq) - hlist_del_rcu(&x->byseq); + hlist_del_init_rcu(&x->bydst); + hlist_del_init_rcu(&x->bysrc); + if (!hlist_unhashed(&x->byseq)) + hlist_del_init_rcu(&x->byseq); if (!hlist_unhashed(&x->state_cache)) hlist_del_rcu(&x->state_cache); if (!hlist_unhashed(&x->state_cache_input)) hlist_del_rcu(&x->state_cache_input); - if (x->id.spi) - hlist_del_rcu(&x->byspi); + if (!hlist_unhashed(&x->byspi)) + hlist_del_init_rcu(&x->byspi); net->xfrm.state_num--; xfrm_nat_keepalive_state_updated(x); spin_unlock(&net->xfrm.xfrm_state_lock); -- cgit 1.3-korg
net/xfrm/xfrm_state.c+6 −7 modifieddiff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c index 1748d374abcab3..686014d394298c 100644 --- a/net/xfrm/xfrm_state.c +++ b/net/xfrm/xfrm_state.c @@ -818,17 +818,17 @@ int __xfrm_state_delete(struct xfrm_state *x) spin_lock(&net->xfrm.xfrm_state_lock); list_del(&x->km.all); - hlist_del_rcu(&x->bydst); - hlist_del_rcu(&x->bysrc); - if (x->km.seq) - hlist_del_rcu(&x->byseq); + hlist_del_init_rcu(&x->bydst); + hlist_del_init_rcu(&x->bysrc); + if (!hlist_unhashed(&x->byseq)) + hlist_del_init_rcu(&x->byseq); if (!hlist_unhashed(&x->state_cache)) hlist_del_rcu(&x->state_cache); if (!hlist_unhashed(&x->state_cache_input)) hlist_del_rcu(&x->state_cache_input); - if (x->id.spi) - hlist_del_rcu(&x->byspi); + if (!hlist_unhashed(&x->byspi)) + hlist_del_init_rcu(&x->byspi); net->xfrm.state_num--; xfrm_nat_keepalive_state_updated(x); spin_unlock(&net->xfrm.xfrm_state_lock); -- cgit 1.3-korg
14acf9652e56xfrm: defensively unhash xfrm_state lists in __xfrm_state_delete
2 files changed · +12 −14
net/xfrm/xfrm_state.c+6 −7 modifieddiff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c index 1748d374abcab3..686014d394298c 100644 --- a/net/xfrm/xfrm_state.c +++ b/net/xfrm/xfrm_state.c @@ -818,17 +818,17 @@ int __xfrm_state_delete(struct xfrm_state *x) spin_lock(&net->xfrm.xfrm_state_lock); list_del(&x->km.all); - hlist_del_rcu(&x->bydst); - hlist_del_rcu(&x->bysrc); - if (x->km.seq) - hlist_del_rcu(&x->byseq); + hlist_del_init_rcu(&x->bydst); + hlist_del_init_rcu(&x->bysrc); + if (!hlist_unhashed(&x->byseq)) + hlist_del_init_rcu(&x->byseq); if (!hlist_unhashed(&x->state_cache)) hlist_del_rcu(&x->state_cache); if (!hlist_unhashed(&x->state_cache_input)) hlist_del_rcu(&x->state_cache_input); - if (x->id.spi) - hlist_del_rcu(&x->byspi); + if (!hlist_unhashed(&x->byspi)) + hlist_del_init_rcu(&x->byspi); net->xfrm.state_num--; xfrm_nat_keepalive_state_updated(x); spin_unlock(&net->xfrm.xfrm_state_lock); -- cgit 1.3-korg
net/xfrm/xfrm_state.c+6 −7 modifieddiff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c index 1748d374abcab3..686014d394298c 100644 --- a/net/xfrm/xfrm_state.c +++ b/net/xfrm/xfrm_state.c @@ -818,17 +818,17 @@ int __xfrm_state_delete(struct xfrm_state *x) spin_lock(&net->xfrm.xfrm_state_lock); list_del(&x->km.all); - hlist_del_rcu(&x->bydst); - hlist_del_rcu(&x->bysrc); - if (x->km.seq) - hlist_del_rcu(&x->byseq); + hlist_del_init_rcu(&x->bydst); + hlist_del_init_rcu(&x->bysrc); + if (!hlist_unhashed(&x->byseq)) + hlist_del_init_rcu(&x->byseq); if (!hlist_unhashed(&x->state_cache)) hlist_del_rcu(&x->state_cache); if (!hlist_unhashed(&x->state_cache_input)) hlist_del_rcu(&x->state_cache_input); - if (x->id.spi) - hlist_del_rcu(&x->byspi); + if (!hlist_unhashed(&x->byspi)) + hlist_del_init_rcu(&x->byspi); net->xfrm.state_num--; xfrm_nat_keepalive_state_updated(x); spin_unlock(&net->xfrm.xfrm_state_lock); -- cgit 1.3-korg
4980162de555xfrm: defensively unhash xfrm_state lists in __xfrm_state_delete
2 files changed · +12 −14
net/xfrm/xfrm_state.c+6 −7 modifieddiff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c index a00c4fe1ab0ce2..f6ba58f18ac18e 100644 --- a/net/xfrm/xfrm_state.c +++ b/net/xfrm/xfrm_state.c @@ -818,17 +818,17 @@ int __xfrm_state_delete(struct xfrm_state *x) spin_lock(&net->xfrm.xfrm_state_lock); list_del(&x->km.all); - hlist_del_rcu(&x->bydst); - hlist_del_rcu(&x->bysrc); - if (x->km.seq) - hlist_del_rcu(&x->byseq); + hlist_del_init_rcu(&x->bydst); + hlist_del_init_rcu(&x->bysrc); + if (!hlist_unhashed(&x->byseq)) + hlist_del_init_rcu(&x->byseq); if (!hlist_unhashed(&x->state_cache)) hlist_del_rcu(&x->state_cache); if (!hlist_unhashed(&x->state_cache_input)) hlist_del_rcu(&x->state_cache_input); - if (x->id.spi) - hlist_del_rcu(&x->byspi); + if (!hlist_unhashed(&x->byspi)) + hlist_del_init_rcu(&x->byspi); net->xfrm.state_num--; xfrm_nat_keepalive_state_updated(x); spin_unlock(&net->xfrm.xfrm_state_lock); -- cgit 1.3-korg
net/xfrm/xfrm_state.c+6 −7 modifieddiff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c index a00c4fe1ab0ce2..f6ba58f18ac18e 100644 --- a/net/xfrm/xfrm_state.c +++ b/net/xfrm/xfrm_state.c @@ -818,17 +818,17 @@ int __xfrm_state_delete(struct xfrm_state *x) spin_lock(&net->xfrm.xfrm_state_lock); list_del(&x->km.all); - hlist_del_rcu(&x->bydst); - hlist_del_rcu(&x->bysrc); - if (x->km.seq) - hlist_del_rcu(&x->byseq); + hlist_del_init_rcu(&x->bydst); + hlist_del_init_rcu(&x->bysrc); + if (!hlist_unhashed(&x->byseq)) + hlist_del_init_rcu(&x->byseq); if (!hlist_unhashed(&x->state_cache)) hlist_del_rcu(&x->state_cache); if (!hlist_unhashed(&x->state_cache_input)) hlist_del_rcu(&x->state_cache_input); - if (x->id.spi) - hlist_del_rcu(&x->byspi); + if (!hlist_unhashed(&x->byspi)) + hlist_del_init_rcu(&x->byspi); net->xfrm.state_num--; xfrm_nat_keepalive_state_updated(x); spin_unlock(&net->xfrm.xfrm_state_lock); -- cgit 1.3-korg
b4a53add2fa8xfrm: defensively unhash xfrm_state lists in __xfrm_state_delete
2 files changed · +12 −14
net/xfrm/xfrm_state.c+6 −7 modifieddiff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c index ca42c9b8cecc3e..8ba31cf9b31993 100644 --- a/net/xfrm/xfrm_state.c +++ b/net/xfrm/xfrm_state.c @@ -752,12 +752,12 @@ int __xfrm_state_delete(struct xfrm_state *x) x->km.state = XFRM_STATE_DEAD; spin_lock(&net->xfrm.xfrm_state_lock); list_del(&x->km.all); - hlist_del_rcu(&x->bydst); - hlist_del_rcu(&x->bysrc); - if (x->km.seq) - hlist_del_rcu(&x->byseq); - if (x->id.spi) - hlist_del_rcu(&x->byspi); + hlist_del_init_rcu(&x->bydst); + hlist_del_init_rcu(&x->bysrc); + if (!hlist_unhashed(&x->byseq)) + hlist_del_init_rcu(&x->byseq); + if (!hlist_unhashed(&x->byspi)) + hlist_del_init_rcu(&x->byspi); net->xfrm.state_num--; spin_unlock(&net->xfrm.xfrm_state_lock); -- cgit 1.3-korg
net/xfrm/xfrm_state.c+6 −7 modifieddiff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c index ca42c9b8cecc3e..8ba31cf9b31993 100644 --- a/net/xfrm/xfrm_state.c +++ b/net/xfrm/xfrm_state.c @@ -752,12 +752,12 @@ int __xfrm_state_delete(struct xfrm_state *x) x->km.state = XFRM_STATE_DEAD; spin_lock(&net->xfrm.xfrm_state_lock); list_del(&x->km.all); - hlist_del_rcu(&x->bydst); - hlist_del_rcu(&x->bysrc); - if (x->km.seq) - hlist_del_rcu(&x->byseq); - if (x->id.spi) - hlist_del_rcu(&x->byspi); + hlist_del_init_rcu(&x->bydst); + hlist_del_init_rcu(&x->bysrc); + if (!hlist_unhashed(&x->byseq)) + hlist_del_init_rcu(&x->byseq); + if (!hlist_unhashed(&x->byspi)) + hlist_del_init_rcu(&x->byspi); net->xfrm.state_num--; spin_unlock(&net->xfrm.xfrm_state_lock); -- cgit 1.3-korg
a2e2d08fb070xfrm: defensively unhash xfrm_state lists in __xfrm_state_delete
2 files changed · +12 −14
net/xfrm/xfrm_state.c+6 −7 modifieddiff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c index 1748d374abcab3..686014d394298c 100644 --- a/net/xfrm/xfrm_state.c +++ b/net/xfrm/xfrm_state.c @@ -818,17 +818,17 @@ int __xfrm_state_delete(struct xfrm_state *x) spin_lock(&net->xfrm.xfrm_state_lock); list_del(&x->km.all); - hlist_del_rcu(&x->bydst); - hlist_del_rcu(&x->bysrc); - if (x->km.seq) - hlist_del_rcu(&x->byseq); + hlist_del_init_rcu(&x->bydst); + hlist_del_init_rcu(&x->bysrc); + if (!hlist_unhashed(&x->byseq)) + hlist_del_init_rcu(&x->byseq); if (!hlist_unhashed(&x->state_cache)) hlist_del_rcu(&x->state_cache); if (!hlist_unhashed(&x->state_cache_input)) hlist_del_rcu(&x->state_cache_input); - if (x->id.spi) - hlist_del_rcu(&x->byspi); + if (!hlist_unhashed(&x->byspi)) + hlist_del_init_rcu(&x->byspi); net->xfrm.state_num--; xfrm_nat_keepalive_state_updated(x); spin_unlock(&net->xfrm.xfrm_state_lock); -- cgit 1.3-korg
net/xfrm/xfrm_state.c+6 −7 modifieddiff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c index 1748d374abcab3..686014d394298c 100644 --- a/net/xfrm/xfrm_state.c +++ b/net/xfrm/xfrm_state.c @@ -818,17 +818,17 @@ int __xfrm_state_delete(struct xfrm_state *x) spin_lock(&net->xfrm.xfrm_state_lock); list_del(&x->km.all); - hlist_del_rcu(&x->bydst); - hlist_del_rcu(&x->bysrc); - if (x->km.seq) - hlist_del_rcu(&x->byseq); + hlist_del_init_rcu(&x->bydst); + hlist_del_init_rcu(&x->bysrc); + if (!hlist_unhashed(&x->byseq)) + hlist_del_init_rcu(&x->byseq); if (!hlist_unhashed(&x->state_cache)) hlist_del_rcu(&x->state_cache); if (!hlist_unhashed(&x->state_cache_input)) hlist_del_rcu(&x->state_cache_input); - if (x->id.spi) - hlist_del_rcu(&x->byspi); + if (!hlist_unhashed(&x->byspi)) + hlist_del_init_rcu(&x->byspi); net->xfrm.state_num--; xfrm_nat_keepalive_state_updated(x); spin_unlock(&net->xfrm.xfrm_state_lock); -- cgit 1.3-korg
4980162de555xfrm: defensively unhash xfrm_state lists in __xfrm_state_delete
2 files changed · +12 −14
net/xfrm/xfrm_state.c+6 −7 modifieddiff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c index a00c4fe1ab0ce2..f6ba58f18ac18e 100644 --- a/net/xfrm/xfrm_state.c +++ b/net/xfrm/xfrm_state.c @@ -818,17 +818,17 @@ int __xfrm_state_delete(struct xfrm_state *x) spin_lock(&net->xfrm.xfrm_state_lock); list_del(&x->km.all); - hlist_del_rcu(&x->bydst); - hlist_del_rcu(&x->bysrc); - if (x->km.seq) - hlist_del_rcu(&x->byseq); + hlist_del_init_rcu(&x->bydst); + hlist_del_init_rcu(&x->bysrc); + if (!hlist_unhashed(&x->byseq)) + hlist_del_init_rcu(&x->byseq); if (!hlist_unhashed(&x->state_cache)) hlist_del_rcu(&x->state_cache); if (!hlist_unhashed(&x->state_cache_input)) hlist_del_rcu(&x->state_cache_input); - if (x->id.spi) - hlist_del_rcu(&x->byspi); + if (!hlist_unhashed(&x->byspi)) + hlist_del_init_rcu(&x->byspi); net->xfrm.state_num--; xfrm_nat_keepalive_state_updated(x); spin_unlock(&net->xfrm.xfrm_state_lock); -- cgit 1.3-korg
net/xfrm/xfrm_state.c+6 −7 modifieddiff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c index a00c4fe1ab0ce2..f6ba58f18ac18e 100644 --- a/net/xfrm/xfrm_state.c +++ b/net/xfrm/xfrm_state.c @@ -818,17 +818,17 @@ int __xfrm_state_delete(struct xfrm_state *x) spin_lock(&net->xfrm.xfrm_state_lock); list_del(&x->km.all); - hlist_del_rcu(&x->bydst); - hlist_del_rcu(&x->bysrc); - if (x->km.seq) - hlist_del_rcu(&x->byseq); + hlist_del_init_rcu(&x->bydst); + hlist_del_init_rcu(&x->bysrc); + if (!hlist_unhashed(&x->byseq)) + hlist_del_init_rcu(&x->byseq); if (!hlist_unhashed(&x->state_cache)) hlist_del_rcu(&x->state_cache); if (!hlist_unhashed(&x->state_cache_input)) hlist_del_rcu(&x->state_cache_input); - if (x->id.spi) - hlist_del_rcu(&x->byspi); + if (!hlist_unhashed(&x->byspi)) + hlist_del_init_rcu(&x->byspi); net->xfrm.state_num--; xfrm_nat_keepalive_state_updated(x); spin_unlock(&net->xfrm.xfrm_state_lock); -- cgit 1.3-korg
14acf9652e56xfrm: defensively unhash xfrm_state lists in __xfrm_state_delete
2 files changed · +12 −14
net/xfrm/xfrm_state.c+6 −7 modifieddiff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c index 1748d374abcab3..686014d394298c 100644 --- a/net/xfrm/xfrm_state.c +++ b/net/xfrm/xfrm_state.c @@ -818,17 +818,17 @@ int __xfrm_state_delete(struct xfrm_state *x) spin_lock(&net->xfrm.xfrm_state_lock); list_del(&x->km.all); - hlist_del_rcu(&x->bydst); - hlist_del_rcu(&x->bysrc); - if (x->km.seq) - hlist_del_rcu(&x->byseq); + hlist_del_init_rcu(&x->bydst); + hlist_del_init_rcu(&x->bysrc); + if (!hlist_unhashed(&x->byseq)) + hlist_del_init_rcu(&x->byseq); if (!hlist_unhashed(&x->state_cache)) hlist_del_rcu(&x->state_cache); if (!hlist_unhashed(&x->state_cache_input)) hlist_del_rcu(&x->state_cache_input); - if (x->id.spi) - hlist_del_rcu(&x->byspi); + if (!hlist_unhashed(&x->byspi)) + hlist_del_init_rcu(&x->byspi); net->xfrm.state_num--; xfrm_nat_keepalive_state_updated(x); spin_unlock(&net->xfrm.xfrm_state_lock); -- cgit 1.3-korg
net/xfrm/xfrm_state.c+6 −7 modifieddiff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c index 1748d374abcab3..686014d394298c 100644 --- a/net/xfrm/xfrm_state.c +++ b/net/xfrm/xfrm_state.c @@ -818,17 +818,17 @@ int __xfrm_state_delete(struct xfrm_state *x) spin_lock(&net->xfrm.xfrm_state_lock); list_del(&x->km.all); - hlist_del_rcu(&x->bydst); - hlist_del_rcu(&x->bysrc); - if (x->km.seq) - hlist_del_rcu(&x->byseq); + hlist_del_init_rcu(&x->bydst); + hlist_del_init_rcu(&x->bysrc); + if (!hlist_unhashed(&x->byseq)) + hlist_del_init_rcu(&x->byseq); if (!hlist_unhashed(&x->state_cache)) hlist_del_rcu(&x->state_cache); if (!hlist_unhashed(&x->state_cache_input)) hlist_del_rcu(&x->state_cache_input); - if (x->id.spi) - hlist_del_rcu(&x->byspi); + if (!hlist_unhashed(&x->byspi)) + hlist_del_init_rcu(&x->byspi); net->xfrm.state_num--; xfrm_nat_keepalive_state_updated(x); spin_unlock(&net->xfrm.xfrm_state_lock); -- cgit 1.3-korg
26edb0a3c99fxfrm: defensively unhash xfrm_state lists in __xfrm_state_delete
2 files changed · +12 −14
net/xfrm/xfrm_state.c+6 −7 modifieddiff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c index a55c88b43c3394..6a92d88f9e0363 100644 --- a/net/xfrm/xfrm_state.c +++ b/net/xfrm/xfrm_state.c @@ -755,17 +755,17 @@ int __xfrm_state_delete(struct xfrm_state *x) spin_lock(&net->xfrm.xfrm_state_lock); list_del(&x->km.all); - hlist_del_rcu(&x->bydst); - hlist_del_rcu(&x->bysrc); - if (x->km.seq) - hlist_del_rcu(&x->byseq); + hlist_del_init_rcu(&x->bydst); + hlist_del_init_rcu(&x->bysrc); + if (!hlist_unhashed(&x->byseq)) + hlist_del_init_rcu(&x->byseq); if (!hlist_unhashed(&x->state_cache)) hlist_del_rcu(&x->state_cache); if (!hlist_unhashed(&x->state_cache_input)) hlist_del_rcu(&x->state_cache_input); - if (x->id.spi) - hlist_del_rcu(&x->byspi); + if (!hlist_unhashed(&x->byspi)) + hlist_del_init_rcu(&x->byspi); net->xfrm.state_num--; xfrm_nat_keepalive_state_updated(x); spin_unlock(&net->xfrm.xfrm_state_lock); -- cgit 1.3-korg
net/xfrm/xfrm_state.c+6 −7 modifieddiff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c index a55c88b43c3394..6a92d88f9e0363 100644 --- a/net/xfrm/xfrm_state.c +++ b/net/xfrm/xfrm_state.c @@ -755,17 +755,17 @@ int __xfrm_state_delete(struct xfrm_state *x) spin_lock(&net->xfrm.xfrm_state_lock); list_del(&x->km.all); - hlist_del_rcu(&x->bydst); - hlist_del_rcu(&x->bysrc); - if (x->km.seq) - hlist_del_rcu(&x->byseq); + hlist_del_init_rcu(&x->bydst); + hlist_del_init_rcu(&x->bysrc); + if (!hlist_unhashed(&x->byseq)) + hlist_del_init_rcu(&x->byseq); if (!hlist_unhashed(&x->state_cache)) hlist_del_rcu(&x->state_cache); if (!hlist_unhashed(&x->state_cache_input)) hlist_del_rcu(&x->state_cache_input); - if (x->id.spi) - hlist_del_rcu(&x->byspi); + if (!hlist_unhashed(&x->byspi)) + hlist_del_init_rcu(&x->byspi); net->xfrm.state_num--; xfrm_nat_keepalive_state_updated(x); spin_unlock(&net->xfrm.xfrm_state_lock); -- cgit 1.3-korg
Vulnerability mechanics
Root cause
"Use of value-based predicates instead of list-state checks in __xfrm_state_delete() allows double-unhash of hlist nodes, causing a write through LIST_POISON pointers and slab-use-after-free."
Attack vector
An attacker can trigger a slab-use-after-free by causing `__xfrm_state_delete()` to be called twice on the same `xfrm_state` object, or by having `xfrm_alloc_spi()` set `x->id.spi` (inserting into `byspi`) while a concurrent deletion path observes a stale non-zero `spi` value and attempts to unhash a node that is no longer on the list [patch_id=2898575]. The original code's value-based predicates (`if (x->km.seq)` / `if (x->id.spi)`) are inconsistent with actual list state, allowing a second `hlist_del_rcu()` to write through `LIST_POISON` pointers. The bug is reachable via the network namespace cleanup path (`cleanup_net` -> `xfrm_state_fini` -> `xfrm_state_flush` -> `xfrm_state_delete` -> `__xfrm_state_delete`).
Affected code
The vulnerability is in the `__xfrm_state_delete()` function in `net/xfrm/xfrm_state.c` [patch_id=2898575]. The function uses `hlist_del_rcu()` on the `bydst`, `bysrc`, `byseq`, and `byspi` hash chain nodes, and guards the `byseq`/`byspi` unhashes with value-based predicates (`x->km.seq` and `x->id.spi`) rather than checking actual list membership.
What the fix does
The patch makes two defensive changes in `__xfrm_state_delete()` [patch_id=2898575]. First, it replaces `hlist_del_rcu()` with `hlist_del_init_rcu()` for the `bydst`, `bysrc`, `byseq`, and `byspi` nodes, so that a second deletion is a no-op (the node is already unhashed and `pprev` points to the node itself) rather than a write through `LIST_POISON`. Second, it changes the guard predicates for `byseq` and `byspi` from value-based checks (`x->km.seq` / `x->id.spi`) to list-state checks (`!hlist_unhashed()`), ensuring the unhash decision tracks whether the node is actually on a list rather than mutable scalar fields that may be set before insertion.
Preconditions
- inputThe attacker must be able to trigger concurrent or repeated calls to __xfrm_state_delete() on the same xfrm_state object, e.g. via network namespace teardown racing with xfrm state manipulation
- authThe system must have xfrm (IPsec) state objects created and then deleted, which requires the NET_NS capability or root privileges in a container
Generated on May 28, 2026. Inputs: CWE entries + fix-commit diffs from this CVE's patches. Citations validated against bundle.
References
5- git.kernel.org/stable/c/14acf9652e5690de3c7486c6db5fb8dafd0a32a3nvd
- git.kernel.org/stable/c/26edb0a3c99f9d958c212be68b21f1221614dcf0nvd
- git.kernel.org/stable/c/4980162de555cb838f1a189ce7d2cbf5d2e7b050nvd
- git.kernel.org/stable/c/a2e2d08fb070fab4947447171f1c4e3ca5a188e5nvd
- git.kernel.org/stable/c/b4a53add2fa8f1b5aa17d4c5686c320785fab182nvd
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