smb: client: sync the root session and superblock context passwords before automounting

In some cases, when password2 becomes the working password, the
client swaps the two password fields in the root session struct, but
not in the smb3_fs_context struct in cifs_sb. DFS automounts inherit
fs context from their parent mounts. Therefore, they might end up
getting the passwords in the stale order.
The automount should succeed, because the mount function will end up
retrying with the actual password anyway. But to reduce these
unnecessary session setup retries for automounts, we can sync the
parent context's passwords with the root session's passwords before
duplicating it to the child's fs context.

Cc: stable@vger.kernel.org
Signed-off-by: Meetakshi Setiya <msetiya@microsoft.com>
Reviewed-by: Shyam Prasad N <sprasad@microsoft.com>
Acked-by: Paulo Alcantara (Red Hat) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: meetakshi253

fs/smb/client/namespace.c

@@ -196,11 +196,28 @@ static struct vfsmount *cifs_do_automount(struct path *path)
 	struct smb3_fs_context tmp;
 	char *full_path;
 	struct vfsmount *mnt;
+	struct cifs_sb_info *mntpt_sb;
+	struct cifs_ses *ses;
 
 	if (IS_ROOT(mntpt))
 		return ERR_PTR(-ESTALE);
 
-	cur_ctx = CIFS_SB(mntpt->d_sb)->ctx;
+	mntpt_sb = CIFS_SB(mntpt->d_sb);
+	ses = cifs_sb_master_tcon(mntpt_sb)->ses;
+	cur_ctx = mntpt_sb->ctx;
+
+	/*
+	 * At this point, the root session should be in the mntpt sb. We should
+	 * bring the sb context passwords in sync with the root session's
+	 * passwords. This would help prevent unnecessary retries and password
+	 * swaps for automounts.
+	 */
+	mutex_lock(&ses->session_mutex);
+	rc = smb3_sync_session_ctx_passwords(mntpt_sb, ses);
+	mutex_unlock(&ses->session_mutex);
+
+	if (rc)
+		return ERR_PTR(rc);
 
 	fc = fs_context_for_submount(path->mnt->mnt_sb->s_type, mntpt);
 	if (IS_ERR(fc))