Re: [PATCH 0/2] cifs: follow-on fixes to time_last_write mechanism

Tentatively merged into cifs-2.6.git for-next pending testing

On Mon, Jul 27, 2026 at 1:22=E2=80=AFPM Paulo Alcantara <[email protected]> =
wrote:
>
> Frank Sorenson <[email protected]> writes:
>
> > This series addresses two correctness issues in commit e8a8d54c2d50
> > ("cifs: prevent readdir from changing file size due to stale directory
> > metadata"), which introduced the time_last_write field to protect cache=
d
> > file sizes from stale Windows Server directory enumeration metadata.
> >
> > Patch 1 consolidates the time_last_write stamp into _cifsFileInfo_put()=
.
> > The original commit scattered the stamp across cifs_close(),
> > smb2_deferred_work_close(), and three deferred-close drain functions in
> > misc.c.  This missed the case where background I/O holds the final file
> > reference after userspace close() returns -- the stamp was anchored to
> > the earlier userspace-close time rather than the actual server close,
> > allowing the protection window to expire before the handle was removed
> > from openFileList.  Moving the stamp into _cifsFileInfo_put() under
> > open_file_lock provides a single canonical location that covers all clo=
se
> > paths and uses the spinlock's store-release/load-acquire pairing with
> > is_inode_writable() for correct memory ordering.
> >
> > Patch 2 fixes the stamp placement in the setattr/truncate paths.
> > cifs_file_set_size() calls cifs_setsize() on success, which calls
> > i_size_write() and updates i_size.  The subsequent check
> > attrs->ia_size !=3D i_size_read() therefore always evaluates false afte=
r a
> > successful cifs_file_set_size(), making the stamp dead code -- the
> > truncate path was completely unprotected.  The fix moves the stamp to
> > before the RPC call, guarded by attrs->ia_size !=3D i_size_read() to
> > exclude no-op same-size ftruncate(2) calls.  On failure the stamp is
> > left in place rather than restored: restoring a stale snapshot (prev_tl=
w)
> > could silently erase a concurrent _cifsFileInfo_put() close stamp if th=
at
> > close arrived between the READ_ONCE and the smp_store_release.  readdir
> > is suppressed until the stamp expires; stat() is unaffected because
> > cifs_revalidate_dentry_attr() uses from_readdir=3Dfalse, bypassing the
> > time_last_write check entirely and always returning an authoritative
> > QUERY_INFO result.
> >
> > Frank Sorenson (2):
> >   cifs: consolidate time_last_write stamp into _cifsFileInfo_put()
> >   cifs: fix time_last_write stamp placement in setattr/truncate paths
>
> Reviewed-by: Paulo Alcantara (Red Hat) <[email protected]>
>


--=20
Thanks,

Steve