fsdax: dax_unshare_iter needs to copy entire blocks
The code that copies data from srcmap to iomap in dax_unshare_iter is
very very broken, which bfoster's recent fsx changes have exposed.
If the pos and len passed to dax_file_unshare are not aligned to an
fsblock boundary, the iter pos and length in the _iter function will
reflect this unalignment.
dax_iomap_direct_access always returns a pointer to the start of the
kmapped fsdax page, even if its pos argument is in the middle of that
page. This is catastrophic for data integrity when iter->pos is not
aligned to a page, because daddr/saddr do not point to the same byte in
the file as iter->pos. Hence we corrupt user data by copying it to the
wrong place.
If iter->pos + iomap_length() in the _iter function not aligned to a
page, then we fail to copy a full block, and only partially populate the
destination block. This is catastrophic for data confidentiality
because we expose stale pmem contents.
Fix both of these issues by aligning copy_pos/copy_len to a page
boundary (remember, this is fsdax so 1 fsblock == 1 base page) so that
we always copy full blocks.
We're not done yet -- there's no call to invalidate_inode_pages2_range,
so programs that have the file range mmap'd will continue accessing the
old memory mapping after the file metadata updates have completed.
Be careful with the return value -- if the unshare succeeds, we still
need to return the number of bytes that the iomap iter thinks we're
operating on.
Metrics
Affected Vendors & Products
| Source | ID | Title | 
|---|---|---|
  Debian DLA | 
                DLA-4008-1 | linux-6.1 security update | 
  Debian DSA | 
                DSA-5818-1 | linux security update | 
  Ubuntu USN | 
                USN-7276-1 | Linux kernel vulnerabilities | 
  Ubuntu USN | 
                USN-7277-1 | Linux kernel vulnerabilities | 
  Ubuntu USN | 
                USN-7310-1 | Linux kernel vulnerabilities | 
  Ubuntu USN | 
                USN-7449-1 | Linux kernel vulnerabilities | 
  Ubuntu USN | 
                USN-7449-2 | Linux kernel (HWE) vulnerabilities | 
  Ubuntu USN | 
                USN-7450-1 | Linux kernel vulnerabilities | 
  Ubuntu USN | 
                USN-7451-1 | Linux kernel vulnerabilities | 
  Ubuntu USN | 
                USN-7452-1 | Linux kernel vulnerabilities | 
  Ubuntu USN | 
                USN-7453-1 | Linux kernel (Real-time) vulnerabilities | 
  Ubuntu USN | 
                USN-7468-1 | Linux kernel (Azure, N-Series) vulnerabilities | 
  Ubuntu USN | 
                USN-7523-1 | Linux kernel (Raspberry Pi Real-time) vulnerabilities | 
  Ubuntu USN | 
                USN-7524-1 | Linux kernel (Raspberry Pi) vulnerabilities | 
Solution
No solution given by the vendor.
Workaround
No workaround given by the vendor.
Mon, 03 Nov 2025 23:30:00 +0000
| Type | Values Removed | Values Added | 
|---|---|---|
| References | 
         | 
Wed, 01 Oct 2025 21:15:00 +0000
| Type | Values Removed | Values Added | 
|---|---|---|
| Metrics | 
        
        ssvc
         
  | 
Tue, 15 Jul 2025 13:45:00 +0000
| Type | Values Removed | Values Added | 
|---|---|---|
| Metrics | 
        
        
        epss
         
  | 
    
        
        
        epss
         
  | 
Fri, 22 Nov 2024 15:45:00 +0000
| Type | Values Removed | Values Added | 
|---|---|---|
| Weaknesses | CWE-835 | 
Thu, 14 Nov 2024 17:30:00 +0000
| Type | Values Removed | Values Added | 
|---|---|---|
| First Time appeared | 
        
        Linux
         Linux linux Kernel  | 
|
| Weaknesses | NVD-CWE-noinfo | |
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:6.12:rc1:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:6.12:rc2:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:6.12:rc3:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:6.12:rc4:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:6.12:rc5:*:*:*:*:*:*  | 
|
| Vendors & Products | 
        
        Linux
         Linux linux Kernel  | 
|
| Metrics | 
        
        
        cvssV3_1
         
  | 
    
        
        
        cvssV3_1
         
  | 
Tue, 12 Nov 2024 01:45:00 +0000
| Type | Values Removed | Values Added | 
|---|---|---|
| References | 
         | |
| Metrics | 
        
        
        threat_severity
         
  | 
    
        
        cvssV3_1
         
 
  | 
Sat, 09 Nov 2024 10:30:00 +0000
| Type | Values Removed | Values Added | 
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: fsdax: dax_unshare_iter needs to copy entire blocks The code that copies data from srcmap to iomap in dax_unshare_iter is very very broken, which bfoster's recent fsx changes have exposed. If the pos and len passed to dax_file_unshare are not aligned to an fsblock boundary, the iter pos and length in the _iter function will reflect this unalignment. dax_iomap_direct_access always returns a pointer to the start of the kmapped fsdax page, even if its pos argument is in the middle of that page. This is catastrophic for data integrity when iter->pos is not aligned to a page, because daddr/saddr do not point to the same byte in the file as iter->pos. Hence we corrupt user data by copying it to the wrong place. If iter->pos + iomap_length() in the _iter function not aligned to a page, then we fail to copy a full block, and only partially populate the destination block. This is catastrophic for data confidentiality because we expose stale pmem contents. Fix both of these issues by aligning copy_pos/copy_len to a page boundary (remember, this is fsdax so 1 fsblock == 1 base page) so that we always copy full blocks. We're not done yet -- there's no call to invalidate_inode_pages2_range, so programs that have the file range mmap'd will continue accessing the old memory mapping after the file metadata updates have completed. Be careful with the return value -- if the unshare succeeds, we still need to return the number of bytes that the iomap iter thinks we're operating on. | |
| Title | fsdax: dax_unshare_iter needs to copy entire blocks | |
| References | 
         | 
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2025-11-03T22:27:30.252Z
Reserved: 2024-10-21T19:36:19.979Z
Link: CVE-2024-50250
Updated: 2025-10-01T15:24:53.985Z
Status : Modified
Published: 2024-11-09T11:15:10.833
Modified: 2025-11-03T23:17:06.293
Link: CVE-2024-50250
                        OpenCVE Enrichment
                    No data.
 Debian DLA
 Debian DSA
 Ubuntu USN