CIFS: implement get_dfs_refer for SMB2+

in SMB2+ the get_dfs_refer operation uses a FSCTL. The request can be
made on any Tree Connection according to the specs. Since Samba only
accepted it on an IPC connection until recently, try that first.

https://lists.samba.org/archive/samba-technical/2017-February/118859.html

3.2.4.20.3 Application Requests DFS Referral Information:
> The client MUST search for an existing Session and TreeConnect to any
> share on the server identified by ServerName for the user identified by
> UserCredentials. If no Session and TreeConnect are found, the client
> MUST establish a new Session and TreeConnect to IPC$ on the target
> server as described in section 3.2.4.2 using the supplied ServerName and
> UserCredentials.

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

2 files changed, 109 insertions, 0 deletions

diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
index eba00cd3bd16..b360c381b00e 100644
--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -1104,6 +1104,103 @@ smb2_new_lease_key(struct cifs_fid *fid)
         generate_random_uuid(fid->lease_key);
 }
 
+static int
+smb2_get_dfs_refer(const unsigned int xid, struct cifs_ses *ses,
+                   const char *search_name,
+                   struct dfs_info3_param **target_nodes,
+                   unsigned int *num_of_nodes,
+                   const struct nls_table *nls_codepage, int remap)
+{
+        int rc;
+        __le16 *utf16_path = NULL;
+        int utf16_path_len = 0;
+        struct cifs_tcon *tcon;
+        struct fsctl_get_dfs_referral_req *dfs_req = NULL;
+        struct get_dfs_referral_rsp *dfs_rsp = NULL;
+        u32 dfs_req_size = 0, dfs_rsp_size = 0;
+
+        cifs_dbg(FYI, "smb2_get_dfs_refer path <%s>\n", search_name);
+
+        /*
+         * Use any tcon from the current session. Here, the first one.
+         */
+        spin_lock(&cifs_tcp_ses_lock);
+        tcon = list_first_entry_or_null(&ses->tcon_list, struct cifs_tcon,
+                                        tcon_list);
+        if (tcon)
+                tcon->tc_count++;
+        spin_unlock(&cifs_tcp_ses_lock);
+
+        if (!tcon) {
+                cifs_dbg(VFS, "session %p has no tcon available for a dfs referral request\n",
+                         ses);
+                rc = -ENOTCONN;
+                goto out;
+        }
+
+        utf16_path = cifs_strndup_to_utf16(search_name, PATH_MAX,
+                                           &utf16_path_len,
+                                           nls_codepage, remap);
+        if (!utf16_path) {
+                rc = -ENOMEM;
+                goto out;
+        }
+
+        dfs_req_size = sizeof(*dfs_req) + utf16_path_len;
+        dfs_req = kzalloc(dfs_req_size, GFP_KERNEL);
+        if (!dfs_req) {
+                rc = -ENOMEM;
+                goto out;
+        }
+
+        /* Highest DFS referral version understood */
+        dfs_req->MaxReferralLevel = DFS_VERSION;
+
+        /* Path to resolve in an UTF-16 null-terminated string */
+        memcpy(dfs_req->RequestFileName, utf16_path, utf16_path_len);
+
+        do {
+                /* try first with IPC */
+                rc = SMB2_ioctl(xid, tcon, NO_FILE_ID, NO_FILE_ID,
+                                FSCTL_DFS_GET_REFERRALS,
+                                true /* is_fsctl */, true /* use_ipc */,
+                                (char *)dfs_req, dfs_req_size,
+                                (char **)&dfs_rsp, &dfs_rsp_size);
+                if (rc == -ENOTCONN) {
+                        /* try with normal tcon */
+                        rc = SMB2_ioctl(xid, tcon, NO_FILE_ID, NO_FILE_ID,
+                                        FSCTL_DFS_GET_REFERRALS,
+                                        true /* is_fsctl */, false /*use_ipc*/,
+                                        (char *)dfs_req, dfs_req_size,
+                                        (char **)&dfs_rsp, &dfs_rsp_size);
+                }
+        } while (rc == -EAGAIN);
+
+        if (rc) {
+                cifs_dbg(VFS, "ioctl error in smb2_get_dfs_refer rc=%d\n", rc);
+                goto out;
+        }
+
+        rc = parse_dfs_referrals(dfs_rsp, dfs_rsp_size,
+                                 num_of_nodes, target_nodes,
+                                 nls_codepage, remap, search_name,
+                                 true /* is_unicode */);
+        if (rc) {
+                cifs_dbg(VFS, "parse error in smb2_get_dfs_refer rc=%d\n", rc);
+                goto out;
+        }
+
+ out:
+        if (tcon) {
+                spin_lock(&cifs_tcp_ses_lock);
+                tcon->tc_count--;
+                spin_unlock(&cifs_tcp_ses_lock);
+        }
+        kfree(utf16_path);
+        kfree(dfs_req);
+        kfree(dfs_rsp);
+        return rc;
+}
 #define SMB2_SYMLINK_STRUCT_SIZE \
         (sizeof(struct smb2_err_rsp) - 1 + sizeof(struct smb2_symlink_err_rsp))
 
@@ -2283,6 +2380,7 @@ struct smb_version_operations smb20_operations = {
         .clone_range = smb2_clone_range,
         .wp_retry_size = smb2_wp_retry_size,
         .dir_needs_close = smb2_dir_needs_close,
+        .get_dfs_refer = smb2_get_dfs_refer,
 };
 
 struct smb_version_operations smb21_operations = {
@@ -2364,6 +2462,7 @@ struct smb_version_operations smb21_operations = {
         .wp_retry_size = smb2_wp_retry_size,
         .dir_needs_close = smb2_dir_needs_close,
         .enum_snapshots = smb3_enum_snapshots,
+        .get_dfs_refer = smb2_get_dfs_refer,
 };
 
 struct smb_version_operations smb30_operations = {
@@ -2455,6 +2554,7 @@ struct smb_version_operations smb30_operations = {
         .free_transform_rq = smb3_free_transform_rq,
         .is_transform_hdr = smb3_is_transform_hdr,
         .receive_transform = smb3_receive_transform,
+        .get_dfs_refer = smb2_get_dfs_refer,
 };
 
 #ifdef CONFIG_CIFS_SMB311
@@ -2547,6 +2647,7 @@ struct smb_version_operations smb311_operations = {
         .free_transform_rq = smb3_free_transform_rq,
         .is_transform_hdr = smb3_is_transform_hdr,
         .receive_transform = smb3_receive_transform,
+        .get_dfs_refer = smb2_get_dfs_refer,
 };
 #endif /* CIFS_SMB311 */
 
diff --git a/fs/cifs/smb2pdu.h b/fs/cifs/smb2pdu.h
index c03b252501a1..18700fd25a0b 100644
--- a/fs/cifs/smb2pdu.h
+++ b/fs/cifs/smb2pdu.h
@@ -695,6 +695,14 @@ struct fsctl_get_integrity_information_rsp {
 /* Integrity flags for above */
 #define FSCTL_INTEGRITY_FLAG_CHECKSUM_ENFORCEMENT_OFF   0x00000001
 
+/* See MS-DFSC 2.2.2 */
+struct fsctl_get_dfs_referral_req {
+        __le16 MaxReferralLevel;
+        __u8 RequestFileName[];
+} __packed;
+
+/* DFS response is struct get_dfs_refer_rsp */
+
 /* See MS-SMB2 2.2.31.3 */
 struct network_resiliency_req {
         __le32 Timeout;