)]}'
{
  "commit": "14acf9652e5690de3c7486c6db5fb8dafd0a32a3",
  "tree": "1f2e830cf58866ba2d42e787a88f6639c556ab27",
  "parents": [
    "28465227c80fe417b4013c432be1f3737cb9f9a3"
  ],
  "author": {
    "name": "Michal Kosiorek",
    "email": "mkosiorek121@gmail.com",
    "time": "Wed Apr 29 10:54:51 2026 +0200"
  },
  "committer": {
    "name": "Steffen Klassert",
    "email": "steffen.klassert@secunet.com",
    "time": "Wed Apr 29 11:27:34 2026 +0200"
  },
  "message": "xfrm: defensively unhash xfrm_state lists in __xfrm_state_delete\n\nKASAN reproduces a slab-use-after-free in __xfrm_state_delete()\u0027s\nhlist_del_rcu calls under syzkaller load on linux-6.12.y stable\n(reproduced on 6.12.47, also reachable via the same code path on\ntorvalds/master and on the ipsec tree). Nine unique signatures cluster\nin the xfrm_state lifecycle, the load-bearing one being:\n\n  BUG: KASAN: slab-use-after-free in __hlist_del include/linux/list.h:990 [inline]\n  BUG: KASAN: slab-use-after-free in hlist_del_rcu include/linux/rculist.h:516 [inline]\n  BUG: KASAN: slab-use-after-free in __xfrm_state_delete net/xfrm/xfrm_state.c\n  Write of size 8 at addr ffff8881198bcb70 by task kworker/u8:9/435\n\n  Workqueue: netns cleanup_net\n  Call Trace:\n   __hlist_del / hlist_del_rcu\n   __xfrm_state_delete\n   xfrm_state_delete\n   xfrm_state_flush\n   xfrm_state_fini\n   ops_exit_list\n   cleanup_net\n\nThe other observed signatures hit the same slab object from\n__xfrm_state_lookup, xfrm_alloc_spi, __xfrm_state_insert and an OOB\nwrite variant of __xfrm_state_delete, all on the byseq/byspi\nhash chains.\n\n__xfrm_state_delete() guards its byseq and byspi unhashes with\nvalue-based predicates:\n\n\tif (x-\u003ekm.seq)\n\t\thlist_del_rcu(\u0026x-\u003ebyseq);\n\tif (x-\u003eid.spi)\n\t\thlist_del_rcu(\u0026x-\u003ebyspi);\n\nwhile everywhere else in the file (e.g. state_cache, state_cache_input)\nthe safer hlist_unhashed() check is used. xfrm_alloc_spi() sets\nx-\u003eid.spi \u003d newspi inside xfrm_state_lock and then immediately inserts\ninto byspi, but a path that observes x-\u003eid.spi !\u003d 0 outside of\nxfrm_state_lock can still skip-or-hit the byspi unhash inconsistently\nwith whether x is actually on the list. The same holds for x-\u003ekm.seq\nversus byseq, and the bydst/bysrc unhashes have no predicate at all,\nso a second __xfrm_state_delete() on the same object writes through\nLIST_POISON pprev.\n\nThe defensive change here:\n\n  - Use hlist_del_init_rcu() instead of hlist_del_rcu() on bydst,\n    bysrc, byseq and byspi so a second deletion is a no-op rather\n    than a write through LIST_POISON pprev. The byseq/byspi nodes\n    are already initialised in xfrm_state_alloc().\n  - Test hlist_unhashed() rather than the value predicate for\n    byseq/byspi, so the unhash decision tracks list state rather than\n    mutable scalar fields.\n\nEmpirical verification: applied this patch on top of v6.12.47, rebuilt,\nand re-ran the same syzkaller harness for 1h16m on a previously-crashy\nconfiguration that produced ~100 hits each of slab-use-after-free\nRead in xfrm_alloc_spi / Read in __xfrm_state_lookup / Write in\n__xfrm_state_delete. After the patch, 7.1M execs across 32 VMs at\n~1550 exec/sec produced zero xfrm_state UAF/OOB hits. /proc/slabinfo\nconfirms the xfrm_state slab is actively allocated and freed during\nthe run (~143 KiB resident), so the fuzzer is still exercising those\ncode paths -- they just no longer crash.\n\nReproduction:\n\n  - Linux 6.12.47 x86_64 + KASAN_GENERIC + KASAN_INLINE + KCOV\n  - syzkaller @ 746545b8b1e4c3a128db8652b340d3df90ce61db\n  - 32 QEMU/KVM VMs x 2 vCPU on AWS c5.metal bare metal\n  - 9 unique signatures collected in ~9h, all within xfrm_state\n    lifecycle\n\nFixes: fe9f1d8779cb (\"xfrm: add state hashtable keyed by seq\")\nFixes: 7b4dc3600e48 (\"[XFRM]: Do not add a state whose SPI is zero to the SPI hash.\")\nReported-by: Michal Kosiorek \u003cmkosiorek121@gmail.com\u003e\nTested-by: Michal Kosiorek \u003cmkosiorek121@gmail.com\u003e\nCc: stable@vger.kernel.org\nSigned-off-by: Michal Kosiorek \u003cmkosiorek121@gmail.com\u003e\nSigned-off-by: Steffen Klassert \u003csteffen.klassert@secunet.com\u003e\n",
  "tree_diff": [
    {
      "type": "modify",
      "old_id": "1748d374abcab38949d0b9958fce0bbcc3c7e054",
      "old_mode": 33188,
      "old_path": "net/xfrm/xfrm_state.c",
      "new_id": "686014d394298c074d6fab18f99fadedf533c35d",
      "new_mode": 33188,
      "new_path": "net/xfrm/xfrm_state.c"
    }
  ]
}