CIFS: make 'nodfs' mount opt a superblock flag

tcon->Flags is only used by SMB1 code and changing it is not permanent
(you lose the setting on tcon reconnect).

* Move the setting to superblock flags (per mount-points).
* Make automount callback exit early when flag present
* Make dfs resolving happening in mount syscall exit early if flag present

Signed-off-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Acked-by: Pavel Shilovsky <pshilov@microsoft.com>

fs/cifs/cifs_dfs_ref.c

@@ -304,12 +304,17 @@ static struct vfsmount *cifs_dfs_do_automount(struct dentry *mntpt)
 	 */
 	mnt = ERR_PTR(-ENOMEM);
 
+	cifs_sb = CIFS_SB(mntpt->d_sb);
+	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_DFS) {
+		mnt = ERR_PTR(-EREMOTE);
+		goto cdda_exit;
+	}
+
 	/* always use tree name prefix */
 	full_path = build_path_from_dentry_optional_prefix(mntpt, true);
 	if (full_path == NULL)
 		goto cdda_exit;
 
-	cifs_sb = CIFS_SB(mntpt->d_sb);
 	tlink = cifs_sb_tlink(cifs_sb);
 	if (IS_ERR(tlink)) {
 		mnt = ERR_CAST(tlink);

fs/cifs/cifs_fs_sb.h

@@ -51,6 +51,7 @@
 					      */
 #define CIFS_MOUNT_UID_FROM_ACL 0x2000000 /* try to get UID via special SID */
 #define CIFS_MOUNT_NO_HANDLE_CACHE 0x4000000 /* disable caching dir handles */
+#define CIFS_MOUNT_NO_DFS 0x8000000 /* disable DFS resolving */
 
 struct cifs_sb_info {
 	struct rb_root tlink_tree;

fs/cifs/cifsfs.c

@@ -500,6 +500,8 @@ cifs_show_options(struct seq_file *s, struct dentry *root)
 		seq_puts(s, ",unix");
 	else
 		seq_puts(s, ",nounix");
+	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_DFS)
+		seq_puts(s, ",nodfs");
 	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_POSIX_PATHS)
 		seq_puts(s, ",posixpaths");
 	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_SET_UID)

fs/cifs/connect.c

@@ -3086,10 +3086,6 @@ cifs_get_tcon(struct cifs_ses *ses, struct smb_vol *volume_info)
 	if (rc)
 		goto out_fail;
 
-	if (volume_info->nodfs) {
-		tcon->Flags &= ~SMB_SHARE_IS_IN_DFS;
-		cifs_dbg(FYI, "DFS disabled (%d)\n", tcon->Flags);
-	}
 	tcon->use_persistent = false;
 	/* check if SMB2 or later, CIFS does not support persistent handles */
 	if (volume_info->persistent) {
@@ -3664,6 +3660,8 @@ int cifs_setup_cifs_sb(struct smb_vol *pvolume_info,
 	cifs_sb->actimeo = pvolume_info->actimeo;
 	cifs_sb->local_nls = pvolume_info->local_nls;
 
+	if (pvolume_info->nodfs)
+		cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_NO_DFS;
 	if (pvolume_info->noperm)
 		cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_NO_PERM;
 	if (pvolume_info->setuids)
@@ -3820,6 +3818,9 @@ expand_dfs_referral(const unsigned int xid, struct cifs_ses *ses,
 	struct dfs_info3_param *referrals = NULL;
 	char *full_path = NULL, *ref_path = NULL, *mdata = NULL;
 
+	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_DFS)
+		return -EREMOTE;
+
 	full_path = build_unc_path_to_root(volume_info, cifs_sb);
 	if (IS_ERR(full_path))
 		return PTR_ERR(full_path);