smb: client: drain and invalidate before server-side copy/clone

Overview

In the Linux kernel, the following vulnerability has been resolved:

smb: client: drain and invalidate before server-side copy/clone

cifs_file_copychunk_range() and the clone (FICLONE) path of cifs_remap_file_range() do not serialise the destination page cache against the server-side copy the way the other server-side range operations (smb3_zero_range(), smb3_punch_hole(), smb3_collapse_range() and smb3_insert_range()) do.

cifs_file_copychunk_range() invalidates the destination range with filemap_invalidate_inode(), which takes and drops the mapping's invalidate_lock internally, so the lock is no longer held when the copychunk ioctl is issued. It also never drains in-flight netfs I/O on the target. The clone path never takes the invalidate_lock at all (only i_rwsem), uses a bare truncate_inode_pages_range() and likewise does not drain outstanding I/O.

As a result an asynchronous destination writeback can complete after the server-side copy/clone has run and reinstate stale data over the region just written by the server, corrupting the file. This is the same class of corruption as commit d7d2adcd022b ("smb/client: flush dirty data before punching a hole") and has been seen randomly in generic/363 against Windows Server.

Fix both paths to follow the established ordering: hold the target mapping's invalidate_lock across the flush and invalidation of the destination and the server ioctl, and call netfs_wait_for_outstanding_io() on the target to drain in-flight writes before the ioctl is issued. Only the target inode's invalidate_lock is required, as the source is merely flushed and not invalidated; i_rwsem (already held via lock_two_nondirectories()) is acquired before the invalidate_lock, matching the VFS lock ordering. Since filemap_invalidate_inode() takes that same lock internally, replace it with its own unmap/flush/invalidate steps instead of calling it, and return early on a zero-length copy to avoid a range underflow.

Affected

• Linux >= c54fc3a4f375663f2361a9cbb2955fb4ef912879 < dc71660f11ef2fecc0695a41e49cd496a9d255ab
• Linux >= c54fc3a4f375663f2361a9cbb2955fb4ef912879 < c9b1194e8ec99d95db25db45edd2fbf690f043ab
• Linux 358bd5f436d820bb758833050aae065b35d6986c
• Linux 43801359c8971cc49b4a4db5015fba77fbd09c32
• Linux >= 6.1.68 < 6.2
• Linux >= 6.6.7 < 6.7
• Linux 6.7

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.