CVE-2024-47679 (GCVE-0-2024-47679)
Vulnerability from cvelistv5
Published
2024-10-21 11:53
Modified
2026-05-11 20:38
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: vfs: fix race between evice_inodes() and find_inode()&iput() Hi, all Recently I noticed a bug[1] in btrfs, after digged it into and I believe it'a race in vfs. Let's assume there's a inode (ie ino 261) with i_count 1 is called by iput(), and there's a concurrent thread calling generic_shutdown_super(). cpu0: cpu1: iput() // i_count is 1 ->spin_lock(inode) ->dec i_count to 0 ->iput_final() generic_shutdown_super() ->__inode_add_lru() ->evict_inodes() // cause some reason[2] ->if (atomic_read(inode->i_count)) continue; // return before // inode 261 passed the above check // list_lru_add_obj() // and then schedule out ->spin_unlock() // note here: the inode 261 // was still at sb list and hash list, // and I_FREEING|I_WILL_FREE was not been set btrfs_iget() // after some function calls ->find_inode() // found the above inode 261 ->spin_lock(inode) // check I_FREEING|I_WILL_FREE // and passed ->__iget() ->spin_unlock(inode) // schedule back ->spin_lock(inode) // check (I_NEW|I_FREEING|I_WILL_FREE) flags, // passed and set I_FREEING iput() ->spin_unlock(inode) ->spin_lock(inode) ->evict() // dec i_count to 0 ->iput_final() ->spin_unlock() ->evict() Now, we have two threads simultaneously evicting the same inode, which may trigger the BUG(inode->i_state & I_CLEAR) statement both within clear_inode() and iput(). To fix the bug, recheck the inode->i_count after holding i_lock. Because in the most scenarios, the first check is valid, and the overhead of spin_lock() can be reduced. If there is any misunderstanding, please let me know, thanks. [1]: https://lore.kernel.org/linux-btrfs/000000000000eabe1d0619c48986@google.com/ [2]: The reason might be 1. SB_ACTIVE was removed or 2. mapping_shrinkable() return false when I reproduced the bug.
References
Impacted products
Vendor Product Version
Linux Linux Version: 63997e98a3be68d7cec806d22bf9b02b2e1daabb
Version: 63997e98a3be68d7cec806d22bf9b02b2e1daabb
Version: 63997e98a3be68d7cec806d22bf9b02b2e1daabb
Version: 63997e98a3be68d7cec806d22bf9b02b2e1daabb
Version: 63997e98a3be68d7cec806d22bf9b02b2e1daabb
Version: 63997e98a3be68d7cec806d22bf9b02b2e1daabb
Version: 63997e98a3be68d7cec806d22bf9b02b2e1daabb
Version: 63997e98a3be68d7cec806d22bf9b02b2e1daabb
Version: 63997e98a3be68d7cec806d22bf9b02b2e1daabb
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nvfs: fix race between evice_inodes() and find_inode()\u0026iput()\n\nHi, all\n\nRecently I noticed a bug[1] in btrfs, after digged it into\nand I believe it\u0027a race in vfs.\n\nLet\u0027s assume there\u0027s a inode (ie ino 261) with i_count 1 is\ncalled by iput(), and there\u0027s a concurrent thread calling\ngeneric_shutdown_super().\n\ncpu0:                              cpu1:\niput() // i_count is 1\n  -\u003espin_lock(inode)\n  -\u003edec i_count to 0\n  -\u003eiput_final()                    generic_shutdown_super()\n    -\u003e__inode_add_lru()               -\u003eevict_inodes()\n      // cause some reason[2]           -\u003eif (atomic_read(inode-\u003ei_count)) continue;\n      // return before                  // inode 261 passed the above check\n      // list_lru_add_obj()             // and then schedule out\n   -\u003espin_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  -\u003efind_inode()\n    // found the above inode 261\n    -\u003espin_lock(inode)\n   // check I_FREEING|I_WILL_FREE\n   // and passed\n      -\u003e__iget()\n    -\u003espin_unlock(inode)                // schedule back\n                                        -\u003espin_lock(inode)\n                                        // check (I_NEW|I_FREEING|I_WILL_FREE) flags,\n                                        // passed and set I_FREEING\niput()                                  -\u003espin_unlock(inode)\n  -\u003espin_lock(inode)\t\t\t  -\u003eevict()\n  // dec i_count to 0\n  -\u003eiput_final()\n    -\u003espin_unlock()\n    -\u003eevict()\n\nNow, we have two threads simultaneously evicting\nthe same inode, which may trigger the BUG(inode-\u003ei_state \u0026 I_CLEAR)\nstatement both within clear_inode() and iput().\n\nTo fix the bug, recheck the inode-\u003ei_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."
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    "assignerShortName": "Linux",
    "cveId": "CVE-2024-47679",
    "datePublished": "2024-10-21T11:53:22.469Z",
    "dateReserved": "2024-09-30T16:00:12.939Z",
    "dateUpdated": "2026-05-11T20:38:39.732Z",
    "state": "PUBLISHED"
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}


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