Description
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().
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().
Published:
2026-07-19
Score:
n/a
EPSS:
n/a
KEV:
No
Impact:
n/a
Action:
n/a
Analysis
No analysis available yet.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
|
|||||||||||||||
| Linux | Linux | affected |
|
No data.
No data.
No data available yet.
Remediation
No remediation available yet.
Tracking
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Advisories
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References
History
Sun, 19 Jul 2026 12:15:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | 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(). | |
| Title | f2fs: read COW data with the original inode during atomic write | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-07-19T12:02:13.057Z
Reserved: 2026-07-19T07:54:57.013Z
Link: CVE-2026-63811
Vulnrichment
No data.
NVD
No data.
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.