{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2024-53171",
  "modified": "2026-10-09T11:39:44Z",
  "upstream": [
    "CVE-2024-53171"
  ],
  "published": "2024-12-27T13:53:01Z",
  "summary": "ubifs: authentication: Fix use-after-free in ubifs_tnc_end_commit",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nubifs: authentication: Fix use-after-free in ubifs_tnc_end_commit\n\nAfter an insertion in TNC, the tree might split and cause a node to\nchange its `znode->parent`. A further deletion of other nodes in the\ntree (which also could free the nodes), the aforementioned node's\n`znode->cparent` could still point to a freed node. This\n`znode->cparent` may not be updated when getting nodes to commit in\n`ubifs_tnc_start_commit()`. This could then trigger a use-after-free\nwhen accessing the `znode->cparent` in `write_index()` in\n`ubifs_tnc_end_commit()`.\n\nThis can be triggered by running\n\n  rm -f /etc/test-file.bin\n  dd if=/dev/urandom of=/etc/test-file.bin bs=1M count=60 conv=fsync\n\nin a loop, and with `CONFIG_UBIFS_FS_AUTHENTICATION`. KASAN then\nreports:\n\n  BUG: KASAN: use-after-free in ubifs_tnc_end_commit+0xa5c/0x1950\n  Write of size 32 at addr ffffff800a3af86c by task ubifs_bgt0_20/153\n\n  Call trace:\n   dump_backtrace+0x0/0x340\n   show_stack+0x18/0x24\n   dump_stack_lvl+0x9c/0xbc\n   print_address_description.constprop.0+0x74/0x2b0\n   kasan_report+0x1d8/0x1f0\n   kasan_check_range+0xf8/0x1a0\n   memcpy+0x84/0xf4\n   ubifs_tnc_end_commit+0xa5c/0x1950\n   do_commit+0x4e0/0x1340\n   ubifs_bg_thread+0x234/0x2e0\n   kthread+0x36c/0x410\n   ret_from_fork+0x10/0x20\n\n  Allocated by task 401:\n   kasan_save_stack+0x38/0x70\n   __kasan_kmalloc+0x8c/0xd0\n   __kmalloc+0x34c/0x5bc\n   tnc_insert+0x140/0x16a4\n   ubifs_tnc_add+0x370/0x52c\n   ubifs_jnl_write_data+0x5d8/0x870\n   do_writepage+0x36c/0x510\n   ubifs_writepage+0x190/0x4dc\n   __writepage+0x58/0x154\n   write_cache_pages+0x394/0x830\n   do_writepages+0x1f0/0x5b0\n   filemap_fdatawrite_wbc+0x170/0x25c\n   file_write_and_wait_range+0x140/0x190\n   ubifs_fsync+0xe8/0x290\n   vfs_fsync_range+0xc0/0x1e4\n   do_fsync+0x40/0x90\n   __arm64_sys_fsync+0x34/0x50\n   invoke_syscall.constprop.0+0xa8/0x260\n   do_el0_svc+0xc8/0x1f0\n   el0_svc+0x34/0x70\n   el0t_64_sync_handler+0x108/0x114\n   el0t_64_sync+0x1a4/0x1a8\n\n  Freed by task 403:\n   kasan_save_stack+0x38/0x70\n   kasan_set_track+0x28/0x40\n   kasan_set_free_info+0x28/0x4c\n   __kasan_slab_free+0xd4/0x13c\n   kfree+0xc4/0x3a0\n   tnc_delete+0x3f4/0xe40\n   ubifs_tnc_remove_range+0x368/0x73c\n   ubifs_tnc_remove_ino+0x29c/0x2e0\n   ubifs_jnl_delete_inode+0x150/0x260\n   ubifs_evict_inode+0x1d4/0x2e4\n   evict+0x1c8/0x450\n   iput+0x2a0/0x3c4\n   do_unlinkat+0x2cc/0x490\n   __arm64_sys_unlinkat+0x90/0x100\n   invoke_syscall.constprop.0+0xa8/0x260\n   do_el0_svc+0xc8/0x1f0\n   el0_svc+0x34/0x70\n   el0t_64_sync_handler+0x108/0x114\n   el0t_64_sync+0x1a4/0x1a8\n\nThe offending `memcpy()` in `ubifs_copy_hash()` has a use-after-free\nwhen a node becomes root in TNC but still has a `cparent` to an already\nfreed node. More specifically, consider the following TNC:\n\n         zroot\n         /\n        /\n      zp1\n      /\n     /\n    zn\n\nInserting a new node `zn_new` with a key smaller then `zn` will trigger\na split in `tnc_insert()` if `zp1` is full:\n\n         zroot\n         /   \\\n        /     \\\n      zp1     zp2\n      /         \\\n     /           \\\n  zn_new          zn\n\n`zn->parent` has now been moved to `zp2`, *but* `zn->cparent` still\npoints to `zp1`.\n\nNow, consider a removal of all the nodes _except_ `zn`. Just when\n`tnc_delete()` is about to delete `zroot` and `zp2`:\n\n         zroot\n             \\\n              \\\n              zp2\n                \\\n                 \\\n                 zn\n\n`zroot` and `zp2` get freed and the tree collapses:\n\n           zn\n\n`zn` now becomes the new `zroot`.\n\n`get_znodes_to_commit()` will now only find `zn`, the new `zroot`, and\n`write_index()` will check its `znode->cparent` that wrongly points to\nthe already freed `zp1`. `ubifs_copy_hash()` thus gets wrongly called\nwith `znode->cparent->zbranch[znode->iip].hash` that triggers the\nuse-after-free!\n\nFix this by explicitly setting `znode->cparent` to `NULL` in\n`get_znodes_to_commit()` for the root node. The search for the dirty\nnodes\n---truncated---",
  "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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          "1:6.6.62-1+rpt1": {
            "linux_commit": "dd2394360860d15146c96635796a75b05bb32b61",
            "upstream_version": "6.6.62",
            "assessment": "commit ancestry (strak rule)",
            "upstream_fixed": "6.6.64"
          }
        }
      }
    }
  ],
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://www.cve.org/CVERecord?id=CVE-2024-53171"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/daac4aa1825de0dbc1a6eede2fa7f9fc53f14223"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/8d8b3f5f4cbfbf6cb0ea4a4d5dc296872b4151eb"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/4d9807048b851d7a58d5bd089c16254af896e4df"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/74981f7577d183acad1cd58f74c10d263711a215"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/01d3a2293d7e4edfff96618c15727db7e51f11b6"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/398a91599d263e41c5f95a2fd4ebdb6280b5c6c3"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/2497479aecebe869d23a0064e0fd1a03e34f0e2a"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/4617fb8fc15effe8eda4dd898d4e33eb537a7140"
    }
  ],
  "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 vulnerability is reached purely through local filesystem syscalls \u2014 write()/fsync() to grow the TNC, unlink() to free the old parent znode, and sync()/syncfs() to force the commit that performs the dangling write. There is no network-facing or remote path into UBIFS TNC commit.\nAC:L - The attacker fully controls every step: they choose the file creation/deletion sequence that produces the split-then-collapse tree shape (upstream reproduces it with a two-line dd/rm loop), and unprivileged syncfs() forces the commit on demand rather than waiting on the ubifs_bgt background thread, so this is a deterministic dangling-pointer dereference rather than a race against an uncontrolled party.\nPR:L - Only an ordinary unprivileged local account is required \u2014 creating, writing, unlinking files in any writable directory on the mounted UBIFS volume plus a sync()/syncfs() call, all with no capability. Mounting is root-only, but in the realistic deployment (authenticated UBIFS as the embedded rootfs) the filesystem is already mounted at boot.\nUI:N - The attacker performs the entire sequence themselves with their own file operations and their own syncfs() call; no victim action, no separate mount, and no interaction with another user's files is needed.\nS:U - The freed znode and the corrupted slab both live in kernel heap memory managed by the same kernel security authority. No VM, IOMMU, or sandbox boundary is crossed.\nC:H - The use-after-free corrupts a recycled generic-kmalloc object at an attacker-selectable offset, which can be leveraged to smash length, index, or pointer fields of sprayed structures (msg_msg, pipe buffers, keyring payloads) and turn them into an out-of-bounds kernel memory read, disclosing arbitrary kernel data.\nI:H - This is a 32-byte use-after-free WRITE (`memcpy(cparent->zbranch[ciip].hash, hash, 32)`, confirmed by KASAN's \"Write of size 32\") into a freed, spray-reallocatable slab object at one of several attacker-selectable offsets, giving a heap corruption primitive suitable for control-flow hijacking and local privilege escalation.\nA:H - The use-after-free write corrupts arbitrary recycled kernel heap objects and reliably produces oopses or panics, and it fires from the ubifs_bgt kthread or the commit path where failure marks the filesystem COMMIT_BROKEN/read-only, rendering the device unusable."
    }
  }
}