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

rajasimandalos
2026-04-09T10:00:13Z

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