Issue with CIFS mounting of DFS ROOT mount when redirecting from one domain controller to the next

[Thomas Hadig <thomas.hadig@xxxxxxxxxx>]

Hi,

I am using the CIFS module from Linux kernel 3.2.9.

We have the following setup:

In DNS,  domain.net resolves to our secondary AD server   ad2.domain.net
Our primary domain controller is ad1.domain.net and has a DFS redirection set up from \\ad1\share\Users to \\files\share\Users. 

When mounting    \\domain.net\share\Users  I get an error.

I traced this down to the cifs_mount function in fs/cifs/connect.c. In there, rc is set to 0 at the beginning but never reset.
In short, adding an rc=0; line after the label try_mount_again: fixes the issue.

Detailed information:
- Connecting to \\domain.net\share\Users  connects to ad2 with a SMB_COM_NEGOTIATE, SMB_COM_SESSION_SETUP_ANDX, and SMB_COM_TREE_CONNECT_ANDX.
- SMB_COM_TREE_CONNECT_ANDX fails with STATUS_BAD_NETWORK_NAME causing rc to be non-zero and jumping to remote_path_check:
- It connects to ad2's IPC$ share and retrieves the DFS_REFERRAL which leads to \\ad1\share and jumps to try_mount_again:
- It closes the samba session to ad2.
- Now, it connects to ad1 with SMB_COM_NEGOTIATE, SMB_COM_SESSION_SETUP_ANDX, and SMB_COM_TREE_CONNECT_ANDX.
- This time, it succeeds and continues with SMB_COM_TRANSACTION2/ TRANS2_QUERY_FS_INFORMATION/SMB_QUERY_FS_DEVICE_INFO and SMB_QUERY_FS_ATTRIBUTE_INFO.
- It comes to:
        /* check if a whole path is not remote */
        if (!rc && tcon) {
                /* build_path_to_root works only when we have a valid tcon */
                where rc is still non-zero and, thus, does NOT check again for a DFS_REFERRAL.
- I closes the samba session to ad1 and exists with the -6 mount error from the initial tree connect.

The correct behavior would be to reset rc to 0 when connecting to a different samba session.


Patch info:

        rc = bdi_setup_and_register(&cifs_sb->bdi, "cifs", BDI_CAP_MAP_COPY);
        if (rc)
                return rc;

#ifdef CONFIG_CIFS_DFS_UPCALL
try_mount_again:
        /* cleanup activities if we're chasing a referral */
        if (referral_walks_count) {
                if (tcon)
                        cifs_put_tcon(tcon);
                else if (pSesInfo)
                        cifs_put_smb_ses(pSesInfo);
                
                FreeXid(xid);
        }
#endif
        tcon = NULL;
        pSesInfo = NULL;
        srvTcp = NULL;
        full_path = NULL;
        tlink = NULL;
+        rc=0;

        xid = GetXid();

        /* get a reference to a tcp session */
        srvTcp = cifs_get_tcp_session(volume_info);
        if (IS_ERR(srvTcp)) {
                rc = PTR_ERR(srvTcp);
                bdi_destroy(&cifs_sb->bdi);
                goto out;
        }



Thanks
Thomas

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