cifs: fix reconnect with SMB1 UNIX Extensions

When mounting with the SMB1 Unix Extensions (e.g. mounts
to Samba with vers=1.0), reconnects no longer reset the
Unix Extensions (SetFSInfo SET_FILE_UNIX_BASIC) after tcon so most
operations (e.g. stat, ls, open, statfs) will fail continuously
with:
        "Operation not supported"
if the connection ever resets (e.g. due to brief network disconnect)

Cc: stable@vger.kernel.org
Reviewed-by: Paulo Alcantara (Red Hat) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: Steve French

fs/smb/client/connect.c

@@ -3686,6 +3686,7 @@ int cifs_mount(struct cifs_sb_info *cifs_sb, struct smb3_fs_context *ctx)
 }
 #endif
 
+#ifdef CONFIG_CIFS_ALLOW_INSECURE_LEGACY
 /*
  * Issue a TREE_CONNECT request.
  */
@@ -3807,11 +3808,25 @@ CIFSTCon(const unsigned int xid, struct cifs_ses *ses,
 		else
 			tcon->Flags = 0;
 		cifs_dbg(FYI, "Tcon flags: 0x%x\n", tcon->Flags);
-	}
 
+		/*
+		 * reset_cifs_unix_caps calls QFSInfo which requires
+		 * need_reconnect to be false, but we would not need to call
+		 * reset_caps if this were not a reconnect case so must check
+		 * need_reconnect flag here.  The caller will also clear
+		 * need_reconnect when tcon was successful but needed to be
+		 * cleared earlier in the case of unix extensions reconnect
+		 */
+		if (tcon->need_reconnect && tcon->unix_ext) {
+			cifs_dbg(FYI, "resetting caps for %s\n", tcon->tree_name);
+			tcon->need_reconnect = false;
+			reset_cifs_unix_caps(xid, tcon, NULL, NULL);
+		}
+	}
 	cifs_buf_release(smb_buffer);
 	return rc;
 }
+#endif /* CONFIG_CIFS_ALLOW_INSECURE_LEGACY */
 
 static void delayed_free(struct rcu_head *p)
 {