smb: client: fix shared DFS root mounts with different prefixes

When having two DFS root mounts that are connected to same namespace,
same mount options but different prefix paths, we can't really use the
shared @server->origin_fullpath when chasing DFS links in them.

Move the origin_fullpath field to cifs_tcon structure so when having
shared DFS root mounts with different prefix paths, and we need to
chase any DFS links, dfs_get_automount_devname() will pick up the
correct full path out of the @tcon that will be used for the new
mount.

Before patch

  mount.cifs //dom/dfs/dir /mnt/1 -o ...
  mount.cifs //dom/dfs /mnt/2 -o ...
  # shared server, ses, tcon
  # server: origin_fullpath=//dom/dfs/dir

  # @server->origin_fullpath + '/dir/link1'
  $ ls /mnt/2/dir/link1
  ls: cannot open directory '/mnt/2/dir/link1': No such file or directory

After patch

  mount.cifs //dom/dfs/dir /mnt/1 -o ...
  mount.cifs //dom/dfs /mnt/2 -o ...
  # shared server & ses
  # tcon_1: origin_fullpath=//dom/dfs/dir
  # tcon_2: origin_fullpath=//dom/dfs

  # @tcon_2->origin_fullpath + '/dir/link1'
  $ ls /mnt/2/dir/link1
  dir0  dir1  dir10  dir3  dir5  dir6  dir7  dir9  target2_file.txt  tsub

Fixes: 8e3554150d6c ("cifs: fix sharing of DFS connections")
Signed-off-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

1 files changed, 29 insertions, 9 deletions

diff --git a/fs/smb/client/misc.c b/fs/smb/client/misc.c
index 609d0c0d9eca..70dbfe6584f9 100644
--- a/fs/smb/client/misc.c
+++ b/fs/smb/client/misc.c
@@ -156,6 +156,7 @@ tconInfoFree(struct cifs_tcon *tcon)
 #ifdef CONFIG_CIFS_DFS_UPCALL
 	dfs_put_root_smb_sessions(&tcon->dfs_ses_list);
 #endif
+	kfree(tcon->origin_fullpath);
 	kfree(tcon);
 }
 
@@ -1106,20 +1107,25 @@ struct super_cb_data {
 	struct super_block *sb;
 };
 
-static void tcp_super_cb(struct super_block *sb, void *arg)
+static void tcon_super_cb(struct super_block *sb, void *arg)
 {
 	struct super_cb_data *sd = arg;
-	struct TCP_Server_Info *server = sd->data;
 	struct cifs_sb_info *cifs_sb;
-	struct cifs_tcon *tcon;
+	struct cifs_tcon *t1 = sd->data, *t2;
 
 	if (sd->sb)
 		return;
 
 	cifs_sb = CIFS_SB(sb);
-	tcon = cifs_sb_master_tcon(cifs_sb);
-	if (tcon->ses->server == server)
+	t2 = cifs_sb_master_tcon(cifs_sb);
+
+	spin_lock(&t2->tc_lock);
+	if (t1->ses == t2->ses &&
+	    t1->ses->server == t2->ses->server &&
+	    t2->origin_fullpath &&
+	    dfs_src_pathname_equal(t2->origin_fullpath, t1->origin_fullpath))
 		sd->sb = sb;
+	spin_unlock(&t2->tc_lock);
 }
 
 static struct super_block *__cifs_get_super(void (*f)(struct super_block *, void *),
@@ -1145,6 +1151,7 @@ static struct super_block *__cifs_get_super(void (*f)(struct super_block *, void
 			return sd.sb;
 		}
 	}
+	pr_warn_once("%s: could not find dfs superblock\n", __func__);
 	return ERR_PTR(-EINVAL);
 }
 
@@ -1154,9 +1161,15 @@ static void __cifs_put_super(struct super_block *sb)
 		cifs_sb_deactive(sb);
 }
 
-struct super_block *cifs_get_tcp_super(struct TCP_Server_Info *server)
+struct super_block *cifs_get_dfs_tcon_super(struct cifs_tcon *tcon)
 {
-	return __cifs_get_super(tcp_super_cb, server);
+	spin_lock(&tcon->tc_lock);
+	if (!tcon->origin_fullpath) {
+		spin_unlock(&tcon->tc_lock);
+		return ERR_PTR(-ENOENT);
+	}
+	spin_unlock(&tcon->tc_lock);
+	return __cifs_get_super(tcon_super_cb, tcon);
 }
 
 void cifs_put_tcp_super(struct super_block *sb)
@@ -1243,9 +1256,16 @@ int cifs_inval_name_dfs_link_error(const unsigned int xid,
 	 */
 	if (strlen(full_path) < 2 || !cifs_sb ||
 	    (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_DFS) ||
-	    !is_tcon_dfs(tcon) || !ses->server->origin_fullpath)
+	    !is_tcon_dfs(tcon))
 		return 0;
 
+	spin_lock(&tcon->tc_lock);
+	if (!tcon->origin_fullpath) {
+		spin_unlock(&tcon->tc_lock);
+		return 0;
+	}
+	spin_unlock(&tcon->tc_lock);
+
 	/*
 	 * Slow path - tcon is DFS and @full_path has prefix path, so attempt
 	 * to get a referral to figure out whether it is an DFS link.
@@ -1269,7 +1289,7 @@ int cifs_inval_name_dfs_link_error(const unsigned int xid,
 
 		/*
 		 * XXX: we are not using dfs_cache_find() here because we might
-		 * end filling all the DFS cache and thus potentially
+		 * end up filling all the DFS cache and thus potentially
 		 * removing cached DFS targets that the client would eventually
 		 * need during failover.
 		 */