smb: client: guarantee refcounted children from parent session

[ Upstream commit 062a7f0ff46eb57aff526897bd2bebfdb1d3046a ]

Avoid potential use-after-free bugs when walking DFS referrals,
mounting and performing DFS failover by ensuring that all children
from parent @tcon->ses are also refcounted.  They're all needed across
the entire DFS mount.  Get rid of @tcon->dfs_ses_list while we're at
it, too.

Cc: stable@vger.kernel.org # 6.4+
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202404021527.ZlRkIxgv-lkp@intel.com/
Signed-off-by: Paulo Alcantara (Red Hat) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

1 files changed, 20 insertions, 5 deletions

diff --git a/fs/smb/client/connect.c b/fs/smb/client/connect.c
index ae35855966af..c5705de7f9de 100644
--- a/fs/smb/client/connect.c
+++ b/fs/smb/client/connect.c
@@ -1863,6 +1863,9 @@ static int match_session(struct cifs_ses *ses, struct smb3_fs_context *ctx)
 	    ctx->sectype != ses->sectype)
 		return 0;
 
+	if (ctx->dfs_root_ses != ses->dfs_root_ses)
+		return 0;
+
 	/*
 	 * If an existing session is limited to less channels than
 	 * requested, it should not be reused
@@ -2355,9 +2358,9 @@ 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);
+	if (ctx->dfs_root_ses)
+		cifs_smb_ses_inc_refcount(ctx->dfs_root_ses);
 	ses->dfs_root_ses = ctx->dfs_root_ses;
-	if (ses->dfs_root_ses)
-		ses->dfs_root_ses->ses_count++;
 	list_add(&ses->smb_ses_list, &server->smb_ses_list);
 	spin_unlock(&cifs_tcp_ses_lock);
 
@@ -3301,6 +3304,9 @@ void cifs_mount_put_conns(struct cifs_mount_ctx *mnt_ctx)
 		cifs_put_smb_ses(mnt_ctx->ses);
 	else if (mnt_ctx->server)
 		cifs_put_tcp_session(mnt_ctx->server, 0);
+	mnt_ctx->ses = NULL;
+	mnt_ctx->tcon = NULL;
+	mnt_ctx->server = NULL;
 	mnt_ctx->cifs_sb->mnt_cifs_flags &= ~CIFS_MOUNT_POSIX_PATHS;
 	free_xid(mnt_ctx->xid);
 }
@@ -3579,8 +3585,6 @@ int cifs_mount(struct cifs_sb_info *cifs_sb, struct smb3_fs_context *ctx)
 	bool isdfs;
 	int rc;
 
-	INIT_LIST_HEAD(&mnt_ctx.dfs_ses_list);
-
 	rc = dfs_mount_share(&mnt_ctx, &isdfs);
 	if (rc)
 		goto error;
@@ -3611,7 +3615,6 @@ out:
 	return rc;
 
 error:
-	dfs_put_root_smb_sessions(&mnt_ctx.dfs_ses_list);
 	cifs_mount_put_conns(&mnt_ctx);
 	return rc;
 }
@@ -3626,6 +3629,18 @@ int cifs_mount(struct cifs_sb_info *cifs_sb, struct smb3_fs_context *ctx)
 		goto error;
 
 	rc = cifs_mount_get_tcon(&mnt_ctx);
+	if (!rc) {
+		/*
+		 * Prevent superblock from being created with any missing
+		 * connections.
+		 */
+		if (WARN_ON(!mnt_ctx.server))
+			rc = -EHOSTDOWN;
+		else if (WARN_ON(!mnt_ctx.ses))
+			rc = -EACCES;
+		else if (WARN_ON(!mnt_ctx.tcon))
+			rc = -ENOENT;
+	}
 	if (rc)
 		goto error;