{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2024-47679",
  "modified": "2026-10-09T11:39:44Z",
  "upstream": [
    "CVE-2024-47679"
  ],
  "published": "2024-10-21T12:02:02Z",
  "summary": "vfs: fix race between evice_inodes() and find_inode()&iput()",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nvfs: fix race between evice_inodes() and find_inode()&iput()\n\nHi, all\n\nRecently I noticed a bug[1] in btrfs, after digged it into\nand I believe it'a race in vfs.\n\nLet's assume there's a inode (ie ino 261) with i_count 1 is\ncalled by iput(), and there's a concurrent thread calling\ngeneric_shutdown_super().\n\ncpu0:                              cpu1:\niput() // i_count is 1\n  ->spin_lock(inode)\n  ->dec i_count to 0\n  ->iput_final()                    generic_shutdown_super()\n    ->__inode_add_lru()               ->evict_inodes()\n      // cause some reason[2]           ->if (atomic_read(inode->i_count)) continue;\n      // return before                  // inode 261 passed the above check\n      // list_lru_add_obj()             // and then schedule out\n   ->spin_unlock()\n// note here: the inode 261\n// was still at sb list and hash list,\n// and I_FREEING|I_WILL_FREE was not been set\n\nbtrfs_iget()\n  // after some function calls\n  ->find_inode()\n    // found the above inode 261\n    ->spin_lock(inode)\n   // check I_FREEING|I_WILL_FREE\n   // and passed\n      ->__iget()\n    ->spin_unlock(inode)                // schedule back\n                                        ->spin_lock(inode)\n                                        // check (I_NEW|I_FREEING|I_WILL_FREE) flags,\n                                        // passed and set I_FREEING\niput()                                  ->spin_unlock(inode)\n  ->spin_lock(inode)\t\t\t  ->evict()\n  // dec i_count to 0\n  ->iput_final()\n    ->spin_unlock()\n    ->evict()\n\nNow, we have two threads simultaneously evicting\nthe same inode, which may trigger the BUG(inode->i_state & I_CLEAR)\nstatement both within clear_inode() and iput().\n\nTo fix the bug, recheck the inode->i_count after holding i_lock.\nBecause in the most scenarios, the first check is valid, and\nthe overhead of spin_lock() can be reduced.\n\nIf there is any misunderstanding, please let me know, thanks.\n\n[1]: https://lore.kernel.org/linux-btrfs/000000000000eabe1d0619c48986@google.com/\n[2]: The reason might be 1. SB_ACTIVE was removed or 2. mapping_shrinkable()\nreturn false when I reproduced the bug.",
  "severity": [
    {
      "type": "CVSS_V3",
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
    }
  ],
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  "references": [
    {
      "type": "ADVISORY",
      "url": "https://www.cve.org/CVERecord?id=CVE-2024-47679"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/6cc13a80a26e6b48f78c725c01b91987d61563ef"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/489faddb1ae75b0e1a741fe5ca2542a2b5e794a5"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/47a68c75052a660e4c37de41e321582ec9496195"
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      "url": "https://git.kernel.org/stable/c/3721a69403291e2514d13a7c3af50a006ea1153b"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/540fb13120c9eab3ef203f90c00c8e69f37449d1"
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    {
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      "url": "https://git.kernel.org/stable/c/0eed942bc65de1f93eca7bda51344290f9c573bb"
    },
    {
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      "url": "https://git.kernel.org/stable/c/0f8a5b6d0dafa4f533ac82e98f8b812073a7c9d1"
    },
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      "url": "https://git.kernel.org/stable/c/6c857fb12b9137fee574443385d53914356bbe11"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/88b1afbf0f6b221f6c5bb66cc80cd3b38d696687"
    }
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  "database_specific": {
    "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git",
    "upstream_modified": "2026-08-05T11:52:36Z",
    "severity": {
      "source": "kernel CNA",
      "cvss_v3_score": 7.8,
      "cvss_v3_severity": "High",
      "scenario": "AV:L - The race requires local syscalls \u2014 `umount()` to drive `generic_shutdown_super()`\u2192`evict_inodes()` plus concurrent `open()`/`close()` to drive `find_inode()`/`iput()` on the same inode. No network protocol handler reaches this path.\nAC:L - The attacker controls every side of the race: it stages inodes at `i_count==0` with page cache (making `__inode_add_lru()` bail), hammers lookups on them from parallel threads, and issues the unmount itself, retrying the whole cycle indefinitely until the window between the unlocked `atomic_read(&inode->i_count)` and `spin_lock(&inode->i_lock)` is hit; syzbot reproduced it automatically.\nPR:L - An ordinary unprivileged user can mount and unmount FUSE or overlayfs inside a user namespace (`FS_USERNS_MOUNT`, `unshare -Urm`), and FUSE's `iget5_locked()` lookups supply the racing `find_inode()`; no real root or init-namespace capability is needed.\nUI:N - The attacker performs the mount, the file accesses, and the unmount entirely on its own; no action by another user or administrator is required.\nS:U - The corruption stays within the kernel of the same machine \u2014 a standard local kernel memory-safety issue with no crossing of a VM, hypervisor, or IOMMU boundary.\nC:H - Double eviction leads to `destroy_inode()` twice on the same slab object, a double-free/UAF the attacker can reclaim with controlled data, yielding an arbitrary kernel-memory read primitive and disclosure of any data on the system.\nI:H - The same double-free/UAF on the inode cache allows heap grooming and type confusion between the stale inode and a reclaimed object, giving arbitrary kernel write and a realistic path to privilege escalation.\nA:H - The immediate observable effect is `BUG_ON(inode->i_state & I_CLEAR)` in `clear_inode()` and `BUG_ON(inode->i_state != (I_FREEING|I_CLEAR))` in `evict()`, i.e. a kernel panic, and the slab double-free crashes the system even when not exploited further."
    }
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}