CVE-2024-57976 (GCVE-0-2024-57976)
Vulnerability from cvelistv5
Published
2025-02-27 02:07
Modified
2026-08-05 11:47
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: btrfs: do proper folio cleanup when cow_file_range() failed [BUG] When testing with COW fixup marked as BUG_ON() (this is involved with the new pin_user_pages*() change, which should not result new out-of-band dirty pages), I hit a crash triggered by the BUG_ON() from hitting COW fixup path. This BUG_ON() happens just after a failed btrfs_run_delalloc_range(): BTRFS error (device dm-2): failed to run delalloc range, root 348 ino 405 folio 65536 submit_bitmap 6-15 start 90112 len 106496: -28 ------------[ cut here ]------------ kernel BUG at fs/btrfs/extent_io.c:1444! Internal error: Oops - BUG: 00000000f2000800 [#1] SMP CPU: 0 UID: 0 PID: 434621 Comm: kworker/u24:8 Tainted: G OE 6.12.0-rc7-custom+ #86 Hardware name: QEMU KVM Virtual Machine, BIOS unknown 2/2/2022 Workqueue: events_unbound btrfs_async_reclaim_data_space [btrfs] pc : extent_writepage_io+0x2d4/0x308 [btrfs] lr : extent_writepage_io+0x2d4/0x308 [btrfs] Call trace: extent_writepage_io+0x2d4/0x308 [btrfs] extent_writepage+0x218/0x330 [btrfs] extent_write_cache_pages+0x1d4/0x4b0 [btrfs] btrfs_writepages+0x94/0x150 [btrfs] do_writepages+0x74/0x190 filemap_fdatawrite_wbc+0x88/0xc8 start_delalloc_inodes+0x180/0x3b0 [btrfs] btrfs_start_delalloc_roots+0x174/0x280 [btrfs] shrink_delalloc+0x114/0x280 [btrfs] flush_space+0x250/0x2f8 [btrfs] btrfs_async_reclaim_data_space+0x180/0x228 [btrfs] process_one_work+0x164/0x408 worker_thread+0x25c/0x388 kthread+0x100/0x118 ret_from_fork+0x10/0x20 Code: aa1403e1 9402f3ef aa1403e0 9402f36f (d4210000) ---[ end trace 0000000000000000 ]--- [CAUSE] That failure is mostly from cow_file_range(), where we can hit -ENOSPC. Although the -ENOSPC is already a bug related to our space reservation code, let's just focus on the error handling. For example, we have the following dirty range [0, 64K) of an inode, with 4K sector size and 4K page size: 0 16K 32K 48K 64K |///////////////////////////////////////| |#######################################| Where |///| means page are still dirty, and |###| means the extent io tree has EXTENT_DELALLOC flag. - Enter extent_writepage() for page 0 - Enter btrfs_run_delalloc_range() for range [0, 64K) - Enter cow_file_range() for range [0, 64K) - Function btrfs_reserve_extent() only reserved one 16K extent So we created extent map and ordered extent for range [0, 16K) 0 16K 32K 48K 64K |////////|//////////////////////////////| |<- OE ->|##############################| And range [0, 16K) has its delalloc flag cleared. But since we haven't yet submit any bio, involved 4 pages are still dirty. - Function btrfs_reserve_extent() returns with -ENOSPC Now we have to run error cleanup, which will clear all EXTENT_DELALLOC* flags and clear the dirty flags for the remaining ranges: 0 16K 32K 48K 64K |////////| | | | | Note that range [0, 16K) still has its pages dirty. - Some time later, writeback is triggered again for the range [0, 16K) since the page range still has dirty flags. - btrfs_run_delalloc_range() will do nothing because there is no EXTENT_DELALLOC flag. - extent_writepage_io() finds page 0 has no ordered flag Which falls into the COW fixup path, triggering the BUG_ON(). Unfortunately this error handling bug dates back to the introduction of btrfs. Thankfully with the abuse of COW fixup, at least it won't crash the kernel. [FIX] Instead of immediately unlocking the extent and folios, we keep the extent and folios locked until either erroring out or the whole delalloc range finished. When the whole delalloc range finished without error, we just unlock the whole range with PAGE_SET_ORDERED (and PAGE_UNLOCK for !keep_locked cases) ---truncated---
References
Impacted products
Vendor Product Version
Linux Linux Version: 8b62b72b26bcd72082c4a69d179dd906bcc22200
Version: 8b62b72b26bcd72082c4a69d179dd906bcc22200
Version: 8b62b72b26bcd72082c4a69d179dd906bcc22200
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/btrfs/inode.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "10b3772292bf1be45604ba83fd9650eb94382e78",
              "status": "affected",
              "version": "8b62b72b26bcd72082c4a69d179dd906bcc22200",
              "versionType": "git"
            },
            {
              "lessThan": "692cf71173bb41395c855acbbbe197d3aedfa5d4",
              "status": "affected",
              "version": "8b62b72b26bcd72082c4a69d179dd906bcc22200",
              "versionType": "git"
            },
            {
              "lessThan": "06f364284794f149d2abc167c11d556cf20c954b",
              "status": "affected",
              "version": "8b62b72b26bcd72082c4a69d179dd906bcc22200",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/btrfs/inode.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "2.6.32"
            },
            {
              "lessThan": "2.6.32",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.36",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.13.*",
              "status": "unaffected",
              "version": "6.13.2",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "6.14",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.12.36",
                  "versionStartIncluding": "2.6.32",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.13.2",
                  "versionStartIncluding": "2.6.32",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.14",
                  "versionStartIncluding": "2.6.32",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: do proper folio cleanup when cow_file_range() failed\n\n[BUG]\nWhen testing with COW fixup marked as BUG_ON() (this is involved with the\nnew pin_user_pages*() change, which should not result new out-of-band\ndirty pages), I hit a crash triggered by the BUG_ON() from hitting COW\nfixup path.\n\nThis BUG_ON() happens just after a failed btrfs_run_delalloc_range():\n\n  BTRFS error (device dm-2): failed to run delalloc range, root 348 ino 405 folio 65536 submit_bitmap 6-15 start 90112 len 106496: -28\n  ------------[ cut here ]------------\n  kernel BUG at fs/btrfs/extent_io.c:1444!\n  Internal error: Oops - BUG: 00000000f2000800 [#1] SMP\n  CPU: 0 UID: 0 PID: 434621 Comm: kworker/u24:8 Tainted: G           OE      6.12.0-rc7-custom+ #86\n  Hardware name: QEMU KVM Virtual Machine, BIOS unknown 2/2/2022\n  Workqueue: events_unbound btrfs_async_reclaim_data_space [btrfs]\n  pc : extent_writepage_io+0x2d4/0x308 [btrfs]\n  lr : extent_writepage_io+0x2d4/0x308 [btrfs]\n  Call trace:\n   extent_writepage_io+0x2d4/0x308 [btrfs]\n   extent_writepage+0x218/0x330 [btrfs]\n   extent_write_cache_pages+0x1d4/0x4b0 [btrfs]\n   btrfs_writepages+0x94/0x150 [btrfs]\n   do_writepages+0x74/0x190\n   filemap_fdatawrite_wbc+0x88/0xc8\n   start_delalloc_inodes+0x180/0x3b0 [btrfs]\n   btrfs_start_delalloc_roots+0x174/0x280 [btrfs]\n   shrink_delalloc+0x114/0x280 [btrfs]\n   flush_space+0x250/0x2f8 [btrfs]\n   btrfs_async_reclaim_data_space+0x180/0x228 [btrfs]\n   process_one_work+0x164/0x408\n   worker_thread+0x25c/0x388\n   kthread+0x100/0x118\n   ret_from_fork+0x10/0x20\n  Code: aa1403e1 9402f3ef aa1403e0 9402f36f (d4210000)\n  ---[ end trace 0000000000000000 ]---\n\n[CAUSE]\nThat failure is mostly from cow_file_range(), where we can hit -ENOSPC.\n\nAlthough the -ENOSPC is already a bug related to our space reservation\ncode, let\u0027s just focus on the error handling.\n\nFor example, we have the following dirty range [0, 64K) of an inode,\nwith 4K sector size and 4K page size:\n\n   0        16K        32K       48K       64K\n   |///////////////////////////////////////|\n   |#######################################|\n\nWhere |///| means page are still dirty, and |###| means the extent io\ntree has EXTENT_DELALLOC flag.\n\n- Enter extent_writepage() for page 0\n\n- Enter btrfs_run_delalloc_range() for range [0, 64K)\n\n- Enter cow_file_range() for range [0, 64K)\n\n- Function btrfs_reserve_extent() only reserved one 16K extent\n  So we created extent map and ordered extent for range [0, 16K)\n\n   0        16K        32K       48K       64K\n   |////////|//////////////////////////////|\n   |\u003c- OE -\u003e|##############################|\n\n   And range [0, 16K) has its delalloc flag cleared.\n   But since we haven\u0027t yet submit any bio, involved 4 pages are still\n   dirty.\n\n- Function btrfs_reserve_extent() returns with -ENOSPC\n  Now we have to run error cleanup, which will clear all\n  EXTENT_DELALLOC* flags and clear the dirty flags for the remaining\n  ranges:\n\n   0        16K        32K       48K       64K\n   |////////|                              |\n   |        |                              |\n\n  Note that range [0, 16K) still has its pages dirty.\n\n- Some time later, writeback is triggered again for the range [0, 16K)\n  since the page range still has dirty flags.\n\n- btrfs_run_delalloc_range() will do nothing because there is no\n  EXTENT_DELALLOC flag.\n\n- extent_writepage_io() finds page 0 has no ordered flag\n  Which falls into the COW fixup path, triggering the BUG_ON().\n\nUnfortunately this error handling bug dates back to the introduction of\nbtrfs.  Thankfully with the abuse of COW fixup, at least it won\u0027t crash\nthe kernel.\n\n[FIX]\nInstead of immediately unlocking the extent and folios, we keep the extent\nand folios locked until either erroring out or the whole delalloc range\nfinished.\n\nWhen the whole delalloc range finished without error, we just unlock the\nwhole range with PAGE_SET_ORDERED (and PAGE_UNLOCK for !keep_locked\ncases)\n---truncated---"
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The vulnerable code is btrfs\u0027s buffered-write delalloc/writeback path, reached by dirtying pages on a locally mounted btrfs filesystem and letting writeback run. No network-facing protocol handler is involved, so local access to a writable btrfs mount is required.\nAC:L - The attacker fully controls both preconditions \u2014 dirtying a range large enough that cow_file_range() iterates over multiple extent reservations, and driving the filesystem into the partial-allocation failure state (ENOSPC via fill/fragmentation, or ENOMEM in btrfs_create_io_em()/btrfs_alloc_ordered_extent()). Nothing depends on state outside the attacker\u0027s influence.\nPR:L - Only an ordinary unprivileged local account with write access to any btrfs filesystem is needed; btrfs is the default root filesystem on several major distributions, and no capability, mount privilege, or admin operation is required.\nUI:N - Writeback is initiated by the kernel itself (background flusher threads and the btrfs_async_reclaim_data_space/shrink_delalloc reclaim worker) or by the attacker\u0027s own fsync/sync. No action by any other user is required.\nS:U - The corrupted state and its consequences are entirely within the kernel\u0027s own security authority \u2014 no VM, container-image, or IOMMU boundary is crossed.\nC:H - The bug leaves folios dirty outside the filesystem\u0027s reservation and checksum-tracking machinery with the backing ordered extent and extent map already torn down, so page content can be written back through a path btrfs itself declares \"not data checksum safe\" and previously-mapped disk blocks can be exposed; the resulting BUG()/oops additionally dumps kernel register and stack state.\nI:H - Persistent file data and filesystem accounting are corrupted \u2014 dirty pages survive with no delalloc bit, no space reservation and no ordered extent, so subsequent writeback either commits data outside the ordered-extent/checksum machinery or silently discards it via folio_clear_dirty_for_io(), leaving on-disk content inconsistent with what the filesystem tracks.\nA:H - The commit documents a kernel BUG at fs/btrfs/extent_io.c:1444 (oops in a kworker) taken while the folio and extent range are locked, which permanently wedges every subsequent access to that inode and panics the box under panic_on_oops. Even where the COW-fixup fallback masks the oops, the never-cleaned dirty folios are redirtied and requeued indefinitely, spinning the delalloc-shrink reclaim worker in a livelock."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T11:47:06.245Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/10b3772292bf1be45604ba83fd9650eb94382e78"
        },
        {
          "url": "https://git.kernel.org/stable/c/692cf71173bb41395c855acbbbe197d3aedfa5d4"
        },
        {
          "url": "https://git.kernel.org/stable/c/06f364284794f149d2abc167c11d556cf20c954b"
        }
      ],
      "title": "btrfs: do proper folio cleanup when cow_file_range() failed",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2024-57976",
    "datePublished": "2025-02-27T02:07:04.307Z",
    "dateReserved": "2025-02-27T02:04:28.912Z",
    "dateUpdated": "2026-08-05T11:47:06.245Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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