Re: [PATCH 7/9] smb: client: block cache=ro and cache=singleclient on remount

RAJASI MANDAL
2026-04-22T04:34:59Z

Handled in updated Patch 1

On Mon, Apr 13, 2026 at 7:10 PM Meetakshi Setiya
<meetakshisetiyaoss@gmail.com> wrote:
>
> Hey Rajasi,
>
> I guess this is not handling remounts where cache=singleclient/ro is
> not specified i.e. preserving previous behaviour.
>
> To reproduce, mount with cache=ro and remount without providing cache=ro.
>
> sudo mount -t cifs //server/winshare /mnt/mainshare -o
> remount,username=demouser
> mount error(22): Invalid argument
>
> On Thu, Apr 9, 2026 at 3:07 AM <rajasimandalos@gmail.com> wrote:
> >
> > From: Rajasi Mandal <rajasimandal@microsoft.com>
> >
> > cache=ro and cache=singleclient are mount-time environment declarations
> > where the admin promises that the share is read-only or exclusively
> > accessed. The client bypasses server-based coherency (oplocks/leases)
> > and caches aggressively based on this promise.
> >
> > These modes were intentionally excluded from smb3_update_mnt_flags()
> > when it was introduced in commit 2d39f50c2b15 ("cifs: move update of
> > flags into a separate function") — only cache=strict, cache=none and
> > cache=loose were made reconfigurable. However, remount currently
> > silently accepts cache=ro and cache=singleclient without actually
> > applying them, which is confusing.
> >
> > Add explicit checks in smb3_verify_reconfigure_ctx() to reject
> > attempts to change these options during remount with a clear error
> > message.
> >
> > Signed-off-by: Rajasi Mandal <rajasimandal@microsoft.com>
> > ---
> > fs/smb/client/fs_context.c | 8 ++++++++
> > 1 file changed, 8 insertions(+)
> >
> > diff --git a/fs/smb/client/fs_context.c b/fs/smb/client/fs_context.c
> > index ce4842e778c4..2be72733ef2e 100644
> > --- a/fs/smb/client/fs_context.c
> > +++ b/fs/smb/client/fs_context.c
> > @@ -1180,6 +1180,14 @@ static int smb3_verify_reconfigure_ctx(struct fs_context *fc,
> > cifs_errorf(fc, "can not change rdma during remount\n");
> > return -EINVAL;
> > }
> > + if (new_ctx->cache_ro != old_ctx->cache_ro) {
> > + cifs_errorf(fc, "can not change cache=ro during remount\n");
> > + return -EINVAL;
> > + }
> > + if (new_ctx->cache_rw != old_ctx->cache_rw) {
> > + cifs_errorf(fc, "can not change cache=singleclient during remount\n");
> > + return -EINVAL;
> > + }
> >
> > return 0;
> > }
> > --
> > 2.43.0
> >
> >