In the Linux kernel, the following vulnerability has been resolved:
smb: client: flush and commit data before querying allocated ranges
The mode 0 / FALLOC_FL_KEEP_SIZE fallocate emulation for small interior ranges in smb3_simple_fallocate_range() issues FSCTL_QUERY_ALLOCATED_RANGES and zero-fills any sub-range the server reports as an unallocated hole, to force block allocation without changing file contents.
This is unsafe against Windows servers. Per the Win32 documentation, FSCTL_QUERY_ALLOCATED_RANGES only reports ranges that *may* contain nonzero data and is explicitly not coherent with recently written data:
"a call to FSCTL_QUERY_ALLOCATED_RANGES [after writing to a network file] would not necessarily return a correct list of allocated regions. To ensure coherency [...] flush the data to the file"
fsx (generic/363) reproduces the resulting corruption against Windows Server 2022: a range is written, an uncached read returns the data, yet the next FSCTL_QUERY_ALLOCATED_RANGES on that range reports it as a whole hole, so the emulation overwrites live data with zeroes. A network trace confirmed the WRITE, the READ returning data and the query returning an empty range list within microseconds. Samba does not exhibit this; its query is coherent with the written data.
Write back the dirty pages, drain any outstanding I/O and issue an SMB2 FLUSH to force the server to commit the data before querying the allocated ranges, so the query reflects the data actually present.
With this, generic/363 passes against both Windows Server 2022 and Samba over 100000 fsx operations.
Prioritise with Active Threat Intelligence
With curated Threat Intelligence, you can see which vulnerabilities truly put you at risk, prioritize what matters most, and act before attackers do.
Explore Intelligence Hub