cifs: set DFS root session in cifs_get_smb_ses()

BugLink: https://bugs.launchpad.net/bugs/2036450

Set the DFS root session pointer earlier when creating a new SMB
session to prevent racing with smb2_reconnect(), cifs_reconnect_tcon()
and DFS cache refresher.

Signed-off-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Cc: stable@vger.kernel.org # 6.2
Signed-off-by: Steve French <stfrench@microsoft.com>
(cherry picked from commit b56bce5)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
[john-cabaj: context changes]
Signed-off-by: John Cabaj <john.cabaj@canonical.com>

Author: Paulo Alcantara

fs/cifs/cifs_dfs_ref.c

@@ -195,6 +195,7 @@ static struct vfsmount *cifs_dfs_do_automount(struct path *path)
 	tmp.leaf_fullpath = NULL;
 	tmp.UNC = tmp.prepath = NULL;
 	fs_context_set_ids(&tmp);
+	tmp.dfs_root_ses = NULL;
 
 	rc = smb3_fs_context_dup(ctx, &tmp);
 	if (rc) {

fs/cifs/cifsglob.h

@@ -1767,7 +1767,6 @@ struct cifs_mount_ctx {
 	struct TCP_Server_Info *server;
 	struct cifs_ses *ses;
 	struct cifs_tcon *tcon;
-	struct cifs_ses *root_ses;
 	uuid_t mount_id;
 	char *origin_fullpath, *leaf_fullpath;
 };

fs/cifs/connect.c

@@ -2240,6 +2240,7 @@ cifs_get_smb_ses(struct TCP_Server_Info *server, struct smb3_fs_context *ctx)
 	 * need to lock before changing something in the session.
 	 */
 	spin_lock(&cifs_tcp_ses_lock);
+	ses->dfs_root_ses = ctx->dfs_root_ses;
 	list_add(&ses->smb_ses_list, &server->smb_ses_list);
 	spin_unlock(&cifs_tcp_ses_lock);
 

fs/cifs/dfs.c

@@ -95,25 +95,22 @@ static int get_session(struct cifs_mount_ctx *mnt_ctx, const char *full_path)
 	ctx->leaf_fullpath = (char *)full_path;
 	rc = cifs_mount_get_session(mnt_ctx);
 	ctx->leaf_fullpath = NULL;
-	if (!rc) {
-		struct cifs_ses *ses = mnt_ctx->ses;
 
-		mutex_lock(&ses->session_mutex);
-		ses->dfs_root_ses = mnt_ctx->root_ses;
-		mutex_unlock(&ses->session_mutex);
-	}
 	return rc;
 }
 
 static void set_root_ses(struct cifs_mount_ctx *mnt_ctx)
 {
-	if (mnt_ctx->ses) {
+	struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
+	struct cifs_ses *ses = mnt_ctx->ses;
+
+	if (ses) {
 		spin_lock(&cifs_tcp_ses_lock);
-		mnt_ctx->ses->ses_count++;
+		ses->ses_count++;
 		spin_unlock(&cifs_tcp_ses_lock);
-		dfs_cache_add_refsrv_session(&mnt_ctx->mount_id, mnt_ctx->ses);
+		dfs_cache_add_refsrv_session(&mnt_ctx->mount_id, ses);
 	}
-	mnt_ctx->root_ses = mnt_ctx->ses;
+	ctx->dfs_root_ses = mnt_ctx->ses;
 }
 
 static int get_dfs_conn(struct cifs_mount_ctx *mnt_ctx, const char *ref_path, const char *full_path,
@@ -260,7 +257,7 @@ int dfs_mount_share(struct cifs_mount_ctx *mnt_ctx, bool *isdfs)
 	rc = get_session(mnt_ctx, NULL);
 	if (rc)
 		return rc;
-	mnt_ctx->root_ses = mnt_ctx->ses;
+	ctx->dfs_root_ses = mnt_ctx->ses;
 	/*
 	 * If called with 'nodfs' mount option, then skip DFS resolving.  Otherwise unconditionally
 	 * try to get an DFS referral (even cached) to determine whether it is an DFS mount.

fs/cifs/dfs.h

@@ -22,9 +22,10 @@ static inline char *dfs_get_path(struct cifs_sb_info *cifs_sb, const char *path)
 static inline int dfs_get_referral(struct cifs_mount_ctx *mnt_ctx, const char *path,
 				   struct dfs_info3_param *ref, struct dfs_cache_tgt_list *tl)
 {
+	struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
 	struct cifs_sb_info *cifs_sb = mnt_ctx->cifs_sb;
 
-	return dfs_cache_find(mnt_ctx->xid, mnt_ctx->root_ses, cifs_sb->local_nls,
+	return dfs_cache_find(mnt_ctx->xid, ctx->dfs_root_ses, cifs_sb->local_nls,
 			      cifs_remap(cifs_sb), path, ref, tl);
 }
 

fs/cifs/fs_context.h

@@ -267,6 +267,7 @@ struct smb3_fs_context {
 	bool rootfs:1; /* if it's a SMB root file system */
 	bool witness:1; /* use witness protocol */
 	char *leaf_fullpath;
+	struct cifs_ses *dfs_root_ses;
 };
 
 extern const struct fs_parameter_spec smb3_fs_parameters[];