smb: client: prevent new fids from being removed by laundromat

Check if @cfid->time is set in laundromat so we guarantee that only
fully cached fids will be selected for removal.  While we're at it,
add missing locks to protect access of @cfid fields in order to avoid
races with open_cached_dir() and cfids_laundromat_worker(),
respectively.

Signed-off-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Reviewed-by: Shyam Prasad N <sprasad@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: Paulo Alcantara

fs/smb/client/cached_dir.c

@@ -170,15 +170,18 @@ int open_cached_dir(unsigned int xid, struct cifs_tcon *tcon,
 		return -ENOENT;
 	}
 	/*
-	 * At this point we either have a lease already and we can just
-	 * return it. If not we are guaranteed to be the only thread accessing
-	 * this cfid.
+	 * Return cached fid if it has a lease.  Otherwise, it is either a new
+	 * entry or laundromat worker removed it from @cfids->entries.  Caller
+	 * will put last reference if the latter.
 	 */
+	spin_lock(&cfids->cfid_list_lock);
 	if (cfid->has_lease) {
+		spin_unlock(&cfids->cfid_list_lock);
 		*ret_cfid = cfid;
 		kfree(utf16_path);
 		return 0;
 	}
+	spin_unlock(&cfids->cfid_list_lock);
 
 	/*
 	 * Skip any prefix paths in @path as lookup_positive_unlocked() ends up
@@ -295,9 +298,11 @@ int open_cached_dir(unsigned int xid, struct cifs_tcon *tcon,
 			goto oshr_free;
 		}
 	}
+	spin_lock(&cfids->cfid_list_lock);
 	cfid->dentry = dentry;
 	cfid->time = jiffies;
 	cfid->has_lease = true;
+	spin_unlock(&cfids->cfid_list_lock);
 
 oshr_free:
 	kfree(utf16_path);
@@ -306,32 +311,36 @@ int open_cached_dir(unsigned int xid, struct cifs_tcon *tcon,
 	free_rsp_buf(resp_buftype[0], rsp_iov[0].iov_base);
 	free_rsp_buf(resp_buftype[1], rsp_iov[1].iov_base);
 	spin_lock(&cfids->cfid_list_lock);
-	if (rc && !cfid->has_lease) {
-		if (cfid->on_list) {
-			list_del(&cfid->entry);
-			cfid->on_list = false;
-			cfids->num_entries--;
+	if (!cfid->has_lease) {
+		if (rc) {
+			if (cfid->on_list) {
+				list_del(&cfid->entry);
+				cfid->on_list = false;
+				cfids->num_entries--;
+			}
+			rc = -ENOENT;
+		} else {
+			/*
+			 * We are guaranteed to have two references at this
+			 * point. One for the caller and one for a potential
+			 * lease. Release the Lease-ref so that the directory
+			 * will be closed when the caller closes the cached
+			 * handle.
+			 */
+			spin_unlock(&cfids->cfid_list_lock);
+			kref_put(&cfid->refcount, smb2_close_cached_fid);
+			goto out;
 		}
-		rc = -ENOENT;
 	}
 	spin_unlock(&cfids->cfid_list_lock);
-	if (!rc && !cfid->has_lease) {
-		/*
-		 * We are guaranteed to have two references at this point.
-		 * One for the caller and one for a potential lease.
-		 * Release the Lease-ref so that the directory will be closed
-		 * when the caller closes the cached handle.
-		 */
-		kref_put(&cfid->refcount, smb2_close_cached_fid);
-	}
 	if (rc) {
 		if (cfid->is_open)
 			SMB2_close(0, cfid->tcon, cfid->fid.persistent_fid,
 				   cfid->fid.volatile_fid);
 		free_cached_dir(cfid);
 		cfid = NULL;
 	}
-
+out:
 	if (rc == 0) {
 		*ret_cfid = cfid;
 		atomic_inc(&tcon->num_remote_opens);
@@ -583,15 +592,18 @@ static void cfids_laundromat_worker(struct work_struct *work)
 
 	spin_lock(&cfids->cfid_list_lock);
 	list_for_each_entry_safe(cfid, q, &cfids->entries, entry) {
-		if (time_after(jiffies, cfid->time + HZ * dir_cache_timeout)) {
+		if (cfid->time &&
+		    time_after(jiffies, cfid->time + HZ * dir_cache_timeout)) {
+			cfid->on_list = false;
 			list_move(&cfid->entry, &entry);
 			cfids->num_entries--;
+			/* To prevent race with smb2_cached_lease_break() */
+			kref_get(&cfid->refcount);
 		}
 	}
 	spin_unlock(&cfids->cfid_list_lock);
 
 	list_for_each_entry_safe(cfid, q, &entry, entry) {
-		cfid->on_list = false;
 		list_del(&cfid->entry);
 		/*
 		 * Cancel and wait for the work to finish in case we are racing
@@ -608,6 +620,8 @@ static void cfids_laundromat_worker(struct work_struct *work)
 			spin_unlock(&cfids->cfid_list_lock);
 			kref_put(&cfid->refcount, smb2_close_cached_fid);
 		}
+		/* Drop the extra reference opened above */
+		kref_put(&cfid->refcount, smb2_close_cached_fid);
 	}
 	queue_delayed_work(cifsiod_wq, &cfids->laundromat_work,
 			   dir_cache_timeout * HZ);