CVE-2026-63811 (GCVE-0-2026-63811)

Vulnerability from cvelistv5 – Published: 2026-07-19 12:02 – Updated: 2026-07-19 12:02
VLAI
Title
f2fs: read COW data with the original inode during atomic write
Summary
In the Linux kernel, the following vulnerability has been resolved: f2fs: read COW data with the original inode during atomic write When updating an atomic-write file, f2fs_write_begin() may read the previously written data back from the COW inode: prepare_atomic_write_begin() locates the block in the COW inode and sets use_cow, and the read bio is then built with the COW inode: f2fs_submit_page_read(use_cow ? F2FS_I(inode)->cow_inode : inode, ...); and f2fs_grab_read_bio() decides whether to schedule fs-layer decryption (STEP_DECRYPT) for the bio based on that inode via fscrypt_inode_uses_fs_layer_crypto(). However, the folio being filled belongs to the original inode (folio->mapping->host == inode), and the data stored in the COW block was encrypted (or left as plaintext) using the original inode's context, not the COW inode's -- see f2fs_encrypt_one_page(), which keys off fio->page->mapping->host. fscrypt_decrypt_pagecache_blocks() likewise operates on folio->mapping->host. The COW inode is created as a tmpfile in the parent directory and inherits its encryption policy from there. With test_dummy_encryption the newly created COW inode gets the dummy policy and becomes encrypted, while a pre-existing regular file -- created before the policy applied, e.g. already present in the on-disk image -- stays unencrypted. The read path then sets STEP_DECRYPT based on the encrypted COW inode and calls fscrypt_decrypt_pagecache_blocks() on a folio whose host (the unencrypted original inode) has a NULL ->i_crypt_info, dereferencing it: Oops: general protection fault, probably for non-canonical address ... KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f] RIP: 0010:fscrypt_decrypt_pagecache_blocks+0xa0/0x310 Workqueue: f2fs_post_read_wq f2fs_post_read_work Call Trace: fscrypt_decrypt_bio+0x1eb/0x340 f2fs_post_read_work+0xba/0x140 process_one_work+0x91c/0x1a40 worker_thread+0x677/0xe90 kthread+0x2bc/0x3a0 The COW inode is only needed to locate the on-disk block, and that block address is already resolved into @blkaddr by prepare_atomic_write_begin() via __find_data_block(cow_inode, ...); f2fs_submit_page_read() then reads from that physical @blkaddr directly, so the inode argument only selects the post-read crypto context, not which block is fetched. Reading with @inode therefore returns the same (latest, not-yet-committed) COW data, while making both the fs-layer decryption decision and the inline crypto path use the correct (original inode's) key. With the COW inode no longer used at the read site, the use_cow flag has no remaining consumer; drop it from f2fs_write_begin() and prepare_atomic_write_begin().
Severity
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 591fc34e1f98b0d7eef4aa3440bfdff3c5a1cadd , < a92332f32a8d31a7eee47b1dc1d751cb3319908f (git)
Affected: 591fc34e1f98b0d7eef4aa3440bfdff3c5a1cadd , < a41075acde0124d2f8a5f563068a5d63e8ffd57b (git)
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Linux Linux Affected: 6.4
Unaffected: 0 , < 6.4 (semver)
Unaffected: 7.1.3 , ≤ 7.1.* (semver)
Unaffected: 7.2-rc1 , ≤ * (original_commit_for_fix)
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/f2fs/data.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "a92332f32a8d31a7eee47b1dc1d751cb3319908f",
              "status": "affected",
              "version": "591fc34e1f98b0d7eef4aa3440bfdff3c5a1cadd",
              "versionType": "git"
            },
            {
              "lessThan": "a41075acde0124d2f8a5f563068a5d63e8ffd57b",
              "status": "affected",
              "version": "591fc34e1f98b0d7eef4aa3440bfdff3c5a1cadd",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/f2fs/data.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.4"
            },
            {
              "lessThan": "6.4",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.1.*",
              "status": "unaffected",
              "version": "7.1.3",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2-rc1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.1.3",
                  "versionStartIncluding": "6.4",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2-rc1",
                  "versionStartIncluding": "6.4",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nf2fs: read COW data with the original inode during atomic write\n\nWhen updating an atomic-write file, f2fs_write_begin() may read the\npreviously written data back from the COW inode:\nprepare_atomic_write_begin() locates the block in the COW inode and sets\nuse_cow, and the read bio is then built with the COW inode:\n\n\tf2fs_submit_page_read(use_cow ? F2FS_I(inode)-\u003ecow_inode : inode,\n\t\t\t      ...);\n\nand f2fs_grab_read_bio() decides whether to schedule fs-layer decryption\n(STEP_DECRYPT) for the bio based on that inode via\nfscrypt_inode_uses_fs_layer_crypto().\n\nHowever, the folio being filled belongs to the original inode\n(folio-\u003emapping-\u003ehost == inode), and the data stored in the COW block was\nencrypted (or left as plaintext) using the original inode\u0027s context, not\nthe COW inode\u0027s -- see f2fs_encrypt_one_page(), which keys off\nfio-\u003epage-\u003emapping-\u003ehost.  fscrypt_decrypt_pagecache_blocks() likewise\noperates on folio-\u003emapping-\u003ehost.\n\nThe COW inode is created as a tmpfile in the parent directory and inherits\nits encryption policy from there.  With test_dummy_encryption the newly\ncreated COW inode gets the dummy policy and becomes encrypted, while a\npre-existing regular file -- created before the policy applied, e.g.\nalready present in the on-disk image -- stays unencrypted.  The read\npath then sets STEP_DECRYPT based on the encrypted COW inode and calls\nfscrypt_decrypt_pagecache_blocks() on a folio whose host (the unencrypted\noriginal inode) has a NULL -\u003ei_crypt_info, dereferencing it:\n\n  Oops: general protection fault, probably for non-canonical address ...\n  KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]\n  RIP: 0010:fscrypt_decrypt_pagecache_blocks+0xa0/0x310\n  Workqueue: f2fs_post_read_wq f2fs_post_read_work\n  Call Trace:\n   fscrypt_decrypt_bio+0x1eb/0x340\n   f2fs_post_read_work+0xba/0x140\n   process_one_work+0x91c/0x1a40\n   worker_thread+0x677/0xe90\n   kthread+0x2bc/0x3a0\n\nThe COW inode is only needed to locate the on-disk block, and that block\naddress is already resolved into @blkaddr by prepare_atomic_write_begin()\nvia __find_data_block(cow_inode, ...); f2fs_submit_page_read() then reads\nfrom that physical @blkaddr directly, so the inode argument only selects\nthe post-read crypto context, not which block is fetched.  Reading with\n@inode therefore returns the same (latest, not-yet-committed) COW data,\nwhile making both the fs-layer decryption decision and the inline crypto\npath use the correct (original inode\u0027s) key.\n\nWith the COW inode no longer used at the read site, the use_cow flag has no\nremaining consumer; drop it from f2fs_write_begin() and\nprepare_atomic_write_begin()."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-07-19T12:02:13.057Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/a92332f32a8d31a7eee47b1dc1d751cb3319908f"
        },
        {
          "url": "https://git.kernel.org/stable/c/a41075acde0124d2f8a5f563068a5d63e8ffd57b"
        }
      ],
      "title": "f2fs: read COW data with the original inode during atomic write",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-63811",
    "datePublished": "2026-07-19T12:02:13.057Z",
    "dateReserved": "2026-07-19T07:54:57.013Z",
    "dateUpdated": "2026-07-19T12:02:13.057Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-63811",
      "date": "2026-07-21",
      "epss": "0.00106",
      "percentile": "0.01298"
    },
    "microsoft_vex": {
      "current_release_date": "2026-07-20T14:41:46.000Z",
      "cve": "CVE-2026-63811",
      "id": "msrc_CVE-2026-63811",
      "initial_release_date": "2026-07-20T01:02:26.000Z",
      "product_status:known_affected": "1",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "f2fs: read COW data with the original inode during atomic write",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-63811.json",
      "version": "2"
    },
    "nvd": "{\"cve\":{\"id\":\"CVE-2026-63811\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2026-07-19T12:16:54.023\",\"lastModified\":\"2026-07-19T12:16:54.023\",\"vulnStatus\":\"Received\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"In the Linux kernel, the following vulnerability has been resolved:\\n\\nf2fs: read COW data with the original inode during atomic write\\n\\nWhen updating an atomic-write file, f2fs_write_begin() may read the\\npreviously written data back from the COW inode:\\nprepare_atomic_write_begin() locates the block in the COW inode and sets\\nuse_cow, and the read bio is then built with the COW inode:\\n\\n\\tf2fs_submit_page_read(use_cow ? F2FS_I(inode)-\u003ecow_inode : inode,\\n\\t\\t\\t      ...);\\n\\nand f2fs_grab_read_bio() decides whether to schedule fs-layer decryption\\n(STEP_DECRYPT) for the bio based on that inode via\\nfscrypt_inode_uses_fs_layer_crypto().\\n\\nHowever, the folio being filled belongs to the original inode\\n(folio-\u003emapping-\u003ehost == inode), and the data stored in the COW block was\\nencrypted (or left as plaintext) using the original inode\u0027s context, not\\nthe COW inode\u0027s -- see f2fs_encrypt_one_page(), which keys off\\nfio-\u003epage-\u003emapping-\u003ehost.  fscrypt_decrypt_pagecache_blocks() likewise\\noperates on folio-\u003emapping-\u003ehost.\\n\\nThe COW inode is created as a tmpfile in the parent directory and inherits\\nits encryption policy from there.  With test_dummy_encryption the newly\\ncreated COW inode gets the dummy policy and becomes encrypted, while a\\npre-existing regular file -- created before the policy applied, e.g.\\nalready present in the on-disk image -- stays unencrypted.  The read\\npath then sets STEP_DECRYPT based on the encrypted COW inode and calls\\nfscrypt_decrypt_pagecache_blocks() on a folio whose host (the unencrypted\\noriginal inode) has a NULL -\u003ei_crypt_info, dereferencing it:\\n\\n  Oops: general protection fault, probably for non-canonical address ...\\n  KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]\\n  RIP: 0010:fscrypt_decrypt_pagecache_blocks+0xa0/0x310\\n  Workqueue: f2fs_post_read_wq f2fs_post_read_work\\n  Call Trace:\\n   fscrypt_decrypt_bio+0x1eb/0x340\\n   f2fs_post_read_work+0xba/0x140\\n   process_one_work+0x91c/0x1a40\\n   worker_thread+0x677/0xe90\\n   kthread+0x2bc/0x3a0\\n\\nThe COW inode is only needed to locate the on-disk block, and that block\\naddress is already resolved into @blkaddr by prepare_atomic_write_begin()\\nvia __find_data_block(cow_inode, ...); f2fs_submit_page_read() then reads\\nfrom that physical @blkaddr directly, so the inode argument only selects\\nthe post-read crypto context, not which block is fetched.  Reading with\\n@inode therefore returns the same (latest, not-yet-committed) COW data,\\nwhile making both the fs-layer decryption decision and the inline crypto\\npath use the correct (original inode\u0027s) key.\\n\\nWith the COW inode no longer used at the read site, the use_cow flag has no\\nremaining consumer; drop it from f2fs_write_begin() and\\nprepare_atomic_write_begin().\"}],\"affected\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"affectedData\":[{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"unaffected\",\"programFiles\":[\"fs/f2fs/data.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"591fc34e1f98b0d7eef4aa3440bfdff3c5a1cadd\",\"lessThan\":\"a92332f32a8d31a7eee47b1dc1d751cb3319908f\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"591fc34e1f98b0d7eef4aa3440bfdff3c5a1cadd\",\"lessThan\":\"a41075acde0124d2f8a5f563068a5d63e8ffd57b\",\"versionType\":\"git\",\"status\":\"affected\"}]},{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"affected\",\"programFiles\":[\"fs/f2fs/data.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"6.4\",\"status\":\"affected\"},{\"version\":\"0\",\"lessThan\":\"6.4\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.1.3\",\"lessThanOrEqual\":\"7.1.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.2-rc1\",\"lessThanOrEqual\":\"*\",\"versionType\":\"original_commit_for_fix\",\"status\":\"unaffected\"}]}]}],\"metrics\":{},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/a41075acde0124d2f8a5f563068a5d63e8ffd57b\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/a92332f32a8d31a7eee47b1dc1d751cb3319908f\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}",
    "redhat_vex": {
      "aggregate_severity": "None",
      "current_release_date": "2026-07-21T09:08:05+00:00",
      "cve": "CVE-2026-63811",
      "id": "CVE-2026-63811",
      "initial_release_date": "2026-07-19T00:00:00+00:00",
      "product_status:known_not_affected": "274",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: f2fs: read COW data with the original inode during atomic write",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63811.json",
      "version": "3"
    }
  }
}



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