smb: client: clear post-EOF pagecache when extending a file via truncate

cifs_setsize() relied on pagecache_isize_extended() to zero the tail of
the folio straddling the old EOF, but that helper is a no-op on CIFS
(i_blkbits is 14), so data dirtied past EOF through an mmap survived
and became visible once the file was extended.

Use netfs_clear_stale_post_isize() instead, called after i_size is
updated since cifs_setsize() callers hold i_rwsem exclusively for the
whole resize.  truncate_pagecache() is then called as in
truncate_setsize(): a no-op on extend, and it drops the pagecache
beyond the new EOF on shrink.

Also thread old_size as an explicit parameter through cifs_setsize()
and cifs_resize_file_locked(), captured by each caller before its own
resize RPC.  This closes a race where a concurrent stat() could adopt
the RPC's already-updated server size via is_size_safe_to_change()
before cifs_setsize() reads old_size itself.

Closes: https://sashiko.dev/#/patchset/20260921230755.1133425-1-pc%40manguebit.org
Fixes: c510edb9734a ("cifs: call pagecache_isize_extended() in cifs_setsize() when extending")
Reviewed-by: David Howells <dhowells@redhat.com>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Bharath SM <bharathsm@microsoft.com>
Cc: stable@vger.kernel.org

0 files changed, 0 insertions, 0 deletions