{"id":"CVE-2026-63811","state":"PUBLISHED","title":"f2fs: read COW data with the original inode during atomic write","description":"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)->cow_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->mapping->host == inode), and the data stored in the COW block was\nencrypted (or left as plaintext) using the original inode's context, not\nthe COW inode's -- see f2fs_encrypt_one_page(), which keys off\nfio->page->mapping->host.  fscrypt_decrypt_pagecache_blocks() likewise\noperates on folio->mapping->host.\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 ->i_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's) 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().","publishedAt":"2026-07-19T12:02:13.057Z","updatedAt":"2026-10-21T12:42:37.074Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"591fc34e1f98b0d7eef4aa3440bfdff3c5a1cadd","status":"affected","lessThan":"bcc9df992f3cbc43f2ecfe0b22e428e50f326e72","versionType":"git"},{"version":"591fc34e1f98b0d7eef4aa3440bfdff3c5a1cadd","status":"affected","lessThan":"655d55c5740d37ffdf6233ff5fe21cea879407f1","versionType":"git"},{"version":"591fc34e1f98b0d7eef4aa3440bfdff3c5a1cadd","status":"affected","lessThan":"7e4ab3907f44dc243d026048d7f5d477dae9267b","versionType":"git"},{"version":"591fc34e1f98b0d7eef4aa3440bfdff3c5a1cadd","status":"affected","lessThan":"a92332f32a8d31a7eee47b1dc1d751cb3319908f","versionType":"git"},{"version":"591fc34e1f98b0d7eef4aa3440bfdff3c5a1cadd","status":"affected","lessThan":"a41075acde0124d2f8a5f563068a5d63e8ffd57b","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/f2fs/data.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.4","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.4","versionType":"semver"},{"version":"6.6.160","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.114","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.57","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.3","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/f2fs/data.c"]}],"references":["https://git.kernel.org/stable/c/bcc9df992f3cbc43f2ecfe0b22e428e50f326e72","https://git.kernel.org/stable/c/655d55c5740d37ffdf6233ff5fe21cea879407f1","https://git.kernel.org/stable/c/7e4ab3907f44dc243d026048d7f5d477dae9267b","https://git.kernel.org/stable/c/a92332f32a8d31a7eee47b1dc1d751cb3319908f","https://git.kernel.org/stable/c/a41075acde0124d2f8a5f563068a5d63e8ffd57b"],"weaknesses":[],"ingestedAt":"2026-10-29T20:12:41.951Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/63xxx/CVE-2026-63811.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-63811","state":"PUBLISHED","datePublished":"2026-07-19T12:02:13.057Z","dateUpdated":"2026-10-21T12:42:37.074Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-07-19T07:54:57.013Z"},"containers":{"cna":{"title":"f2fs: read COW data with the original inode during atomic write","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)->cow_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->mapping->host == inode), and the data stored in the COW block was\nencrypted (or left as plaintext) using the original inode's context, not\nthe COW inode's -- see f2fs_encrypt_one_page(), which keys off\nfio->page->mapping->host.  fscrypt_decrypt_pagecache_blocks() likewise\noperates on folio->mapping->host.\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 ->i_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's) 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":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"591fc34e1f98b0d7eef4aa3440bfdff3c5a1cadd","status":"affected","lessThan":"bcc9df992f3cbc43f2ecfe0b22e428e50f326e72","versionType":"git"},{"version":"591fc34e1f98b0d7eef4aa3440bfdff3c5a1cadd","status":"affected","lessThan":"655d55c5740d37ffdf6233ff5fe21cea879407f1","versionType":"git"},{"version":"591fc34e1f98b0d7eef4aa3440bfdff3c5a1cadd","status":"affected","lessThan":"7e4ab3907f44dc243d026048d7f5d477dae9267b","versionType":"git"},{"version":"591fc34e1f98b0d7eef4aa3440bfdff3c5a1cadd","status":"affected","lessThan":"a92332f32a8d31a7eee47b1dc1d751cb3319908f","versionType":"git"},{"version":"591fc34e1f98b0d7eef4aa3440bfdff3c5a1cadd","status":"affected","lessThan":"a41075acde0124d2f8a5f563068a5d63e8ffd57b","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/f2fs/data.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.4","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.4","versionType":"semver"},{"version":"6.6.160","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.114","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.57","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.3","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/f2fs/data.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/bcc9df992f3cbc43f2ecfe0b22e428e50f326e72"},{"url":"https://git.kernel.org/stable/c/655d55c5740d37ffdf6233ff5fe21cea879407f1"},{"url":"https://git.kernel.org/stable/c/7e4ab3907f44dc243d026048d7f5d477dae9267b"},{"url":"https://git.kernel.org/stable/c/a92332f32a8d31a7eee47b1dc1d751cb3319908f"},{"url":"https://git.kernel.org/stable/c/a41075acde0124d2f8a5f563068a5d63e8ffd57b"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-21T12:42:37.074Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.4","versionEndExcluding":"6.6.160"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.4","versionEndExcluding":"6.12.114"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.4","versionEndExcluding":"6.18.57"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.4","versionEndExcluding":"7.1.3"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.4","versionEndExcluding":"7.2"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}