{
  "affected": [
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:13",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:14",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "7.1.3-1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "details": "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:  \tf2fs_submit_page_read(use_cow ? F2FS_I(inode)-\u003ecow_inode : inode, \t\t\t      ...);  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-\u003emapping-\u003ehost == 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-\u003epage-\u003emapping-\u003ehost.  fscrypt_decrypt_pagecache_blocks() likewise operates on folio-\u003emapping-\u003ehost.  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 -\u003ei_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().",
  "id": "DEBIAN-CVE-2026-63811",
  "modified": "2026-09-14T16:47:40.670513993Z",
  "published": "2026-07-19T12:16:54.023Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://security-tracker.debian.org/tracker/CVE-2026-63811"
    }
  ],
  "upstream": [
    "CVE-2026-63811"
  ]
}