{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2024-49867",
  "modified": "2026-10-07T17:22:01Z",
  "upstream": [
    "CVE-2024-49867"
  ],
  "published": "2024-10-21T18:02:47Z",
  "summary": "btrfs: wait for fixup workers before stopping cleaner kthread during umount",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: wait for fixup workers before stopping cleaner kthread during umount\n\nDuring unmount, at close_ctree(), we have the following steps in this order:\n\n1) Park the cleaner kthread - this doesn't destroy the kthread, it basically\n   halts its execution (wake ups against it work but do nothing);\n\n2) We stop the cleaner kthread - this results in freeing the respective\n   struct task_struct;\n\n3) We call btrfs_stop_all_workers() which waits for any jobs running in all\n   the work queues and then free the work queues.\n\nSyzbot reported a case where a fixup worker resulted in a crash when doing\na delayed iput on its inode while attempting to wake up the cleaner at\nbtrfs_add_delayed_iput(), because the task_struct of the cleaner kthread\nwas already freed. This can happen during unmount because we don't wait\nfor any fixup workers still running before we call kthread_stop() against\nthe cleaner kthread, which stops and free all its resources.\n\nFix this by waiting for any fixup workers at close_ctree() before we call\nkthread_stop() against the cleaner and run pending delayed iputs.\n\nThe stack traces reported by syzbot were the following:\n\n  BUG: KASAN: slab-use-after-free in __lock_acquire+0x77/0x2050 kernel/locking/lockdep.c:5065\n  Read of size 8 at addr ffff8880272a8a18 by task kworker/u8:3/52\n\n  CPU: 1 UID: 0 PID: 52 Comm: kworker/u8:3 Not tainted 6.12.0-rc1-syzkaller #0\n  Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024\n  Workqueue: btrfs-fixup btrfs_work_helper\n  Call Trace:\n   <TASK>\n   __dump_stack lib/dump_stack.c:94 [inline]\n   dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120\n   print_address_description mm/kasan/report.c:377 [inline]\n   print_report+0x169/0x550 mm/kasan/report.c:488\n   kasan_report+0x143/0x180 mm/kasan/report.c:601\n   __lock_acquire+0x77/0x2050 kernel/locking/lockdep.c:5065\n   lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5825\n   __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]\n   _raw_spin_lock_irqsave+0xd5/0x120 kernel/locking/spinlock.c:162\n   class_raw_spinlock_irqsave_constructor include/linux/spinlock.h:551 [inline]\n   try_to_wake_up+0xb0/0x1480 kernel/sched/core.c:4154\n   btrfs_writepage_fixup_worker+0xc16/0xdf0 fs/btrfs/inode.c:2842\n   btrfs_work_helper+0x390/0xc50 fs/btrfs/async-thread.c:314\n   process_one_work kernel/workqueue.c:3229 [inline]\n   process_scheduled_works+0xa63/0x1850 kernel/workqueue.c:3310\n   worker_thread+0x870/0xd30 kernel/workqueue.c:3391\n   kthread+0x2f0/0x390 kernel/kthread.c:389\n   ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147\n   ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244\n   </TASK>\n\n  Allocated by task 2:\n   kasan_save_stack mm/kasan/common.c:47 [inline]\n   kasan_save_track+0x3f/0x80 mm/kasan/common.c:68\n   unpoison_slab_object mm/kasan/common.c:319 [inline]\n   __kasan_slab_alloc+0x66/0x80 mm/kasan/common.c:345\n   kasan_slab_alloc include/linux/kasan.h:247 [inline]\n   slab_post_alloc_hook mm/slub.c:4086 [inline]\n   slab_alloc_node mm/slub.c:4135 [inline]\n   kmem_cache_alloc_node_noprof+0x16b/0x320 mm/slub.c:4187\n   alloc_task_struct_node kernel/fork.c:180 [inline]\n   dup_task_struct+0x57/0x8c0 kernel/fork.c:1107\n   copy_process+0x5d1/0x3d50 kernel/fork.c:2206\n   kernel_clone+0x223/0x880 kernel/fork.c:2787\n   kernel_thread+0x1bc/0x240 kernel/fork.c:2849\n   create_kthread kernel/kthread.c:412 [inline]\n   kthreadd+0x60d/0x810 kernel/kthread.c:765\n   ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147\n   ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244\n\n  Freed by task 61:\n   kasan_save_stack mm/kasan/common.c:47 [inline]\n   kasan_save_track+0x3f/0x80 mm/kasan/common.c:68\n   kasan_save_free_info+0x40/0x50 mm/kasan/generic.c:579\n   poison_slab_object mm/kasan/common.c:247 [inline]\n   __kasan_slab_free+0x59/0x70 mm/kasan/common.c:264\n   kasan_slab_free include/linux/kasan.h:230 [inline]\n   slab_free_h\n---truncated---",
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  "references": [
    {
      "type": "ADVISORY",
      "url": "https://www.cve.org/CVERecord?id=CVE-2024-49867"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/a71349b692ab34ea197949e13e3cc42570fe73d9"
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  "database_specific": {
    "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git",
    "upstream_modified": "2026-08-05T11:52:36Z"
  }
}