From: Michal Kosiorek <mkosiorek121@gmail.com> mainline inclusion from mainline-v7.1-rc3 commit 14acf9652e5690de3c7486c6db5fb8dafd0a32a3 category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/15365 CVE: CVE-2026-46116 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- 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 Fixes: fe9f1d8779cb ("xfrm: add state hashtable keyed by seq") Fixes: 7b4dc3600e48 ("[XFRM]: Do not add a state whose SPI is zero to the SPI hash.") Reported-by: Michal Kosiorek <mkosiorek121@gmail.com> Tested-by: Michal Kosiorek <mkosiorek121@gmail.com> Cc: stable@vger.kernel.org Signed-off-by: Michal Kosiorek <mkosiorek121@gmail.com> Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com> Conflicts: net/xfrm/xfrm_state.c [The OLK-5.10 target lacks commit 3f01d9df5408 ("xfrm: insert a new per-socket policy to the per-socket list after the link is established") which introduced state_cache/state_cache_input unhashing in __xfrm_state_delete(). OLK-5.10 also lacks commit fe9f1d8779cb ("xfrm: add state hashtable keyed by seq") which introduced byseq hash and its unhashing. OLK-5.10 also lacks xfrm_nat_keepalive_state_updated() call. Adapted to only apply the defensive unhashing changes to bydst, bysrc, and byspi lists which are present in OLK-5.10.] Signed-off-by: Dong Chenchen <dongchenchen2@huawei.com> --- net/xfrm/xfrm_state.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c index e3e96606976b..35d26e410738 100644 --- a/net/xfrm/xfrm_state.c +++ b/net/xfrm/xfrm_state.c @@ -672,10 +672,10 @@ 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->id.spi) - hlist_del_rcu(&x->byspi); + hlist_del_init_rcu(&x->bydst); + hlist_del_init_rcu(&x->bysrc); + if (!hlist_unhashed(&x->byspi)) + hlist_del_init_rcu(&x->byspi); net->xfrm.state_num--; spin_unlock(&net->xfrm.xfrm_state_lock); -- 2.43.0