From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 84EA52D5A01; Mon, 17 Aug 2026 14:00:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786975228; cv=none; b=scgwKqvRMyOdDCo3stjUKUwIv55lYRWd2ToSCGbR9Eb/IqRAs9HyQ+8yinnkJvw5tz3S9xHY+00dbfkNEuOBxiOu7ciDfdKzhvQaDC7zZSQPM4I7/+KbPkybg9cSotDZinApmZ8yXiLvO4oetsNO23+vASU2fd0m8+7dbfl5smk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786975228; c=relaxed/simple; bh=AB+ZgZ6T51Y0vgEGKZeWFNc0B1MsKET+at72F/JDWlA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Pz2BPz5nfPCNyYdmeenXt7WkE1bQK9RNSH+7mbKfgy4X7m46TBW2/ou6AqXaWLhaLzDhycZcjJNZCz0SEdowGfjDq4nteazh+LiwcFw0Z26XzmFa9iOmjQKYxUHRHzvFG2Sz9a79alafNkAFxYx5wgc5MP9YODf9YFW+rBq2Ik8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=KUZoE7IP; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="KUZoE7IP" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DCAD81F000E9; Mon, 17 Aug 2026 14:00:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1786975227; bh=sqz6Nx8hAmr4nW/e/tR8Kr5mnTe9WT2CAMDTgT/VNMc=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=KUZoE7IPPAZ+QJI26z86Q5KTy8JKB8V+URZqY7RTwwHJeg+alOq2+nCrb1dNDgTYB vLDxafL7w0PcXknLP0wNHO8cb4HzAcKnqC26U2wVgWOqFD6VVXU9tam3o63nze8XIo loJdb1B5TooHoNOu+Jv/rlOg8oM46W1wO0/wn8uU= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Jan Kara , "Christian Brauner (Amutable)" Subject: [PATCH 6.18 207/250] ovl: dont warn when the mount is completed from another user namespace Date: Mon, 17 Aug 2026 15:32:48 +0200 Message-ID: <20260817132544.995814962@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260817132536.466235697@linuxfoundation.org> References: <20260817132536.466235697@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Christian Brauner commit 63981fc786daaa626cb14d9be1406f674d79f98f upstream. fsopen() records the caller's user namespace in fc->user_ns and hands back an ordinary file descriptor. Nothing ties the task that calls fsconfig(FSCONFIG_CMD_CREATE) to the task that created the context. The fd is inherited across fork() and exec() and it can be passed over a unix socket. Completing a context from another user namespace is allowed on purpose. vfs_cmd_create() authorizes the create with mount_capable(), which for FS_USERNS_MOUNT checks ns_capable(fc->user_ns, CAP_SYS_ADMIN), and that succeeds for a task holding CAP_SYS_ADMIN in an ancestor of fc->user_ns. So an unprivileged task can reach the WARN_ON() in ovl_fill_super(): create a user and a mount namespace in a child, call fsopen("overlay") there, send the fscontext fd to the parent and let the parent issue FSCONFIG_CMD_CREATE. Both namespaces come from a plain unshare(1) and no capability is needed anywhere: WARNING: fs/overlayfs/super.c:1551 at ovl_fill_super+0x7b9/0x1e20 [overlay] CPU: 3 UID: 1000 PID: 3243376 Comm: fswarn Call Trace: get_tree_nodev+0x71/0xa0 ovl_get_tree+0x15/0x20 [overlay] vfs_get_tree+0x2a/0x100 vfs_cmd_create+0x60/0xf0 __do_sys_fsconfig+0x4b2/0x500 The child needs the mount namespace because fsopen() itself gates on may_mount(), which asks for CAP_SYS_ADMIN in the user namespace owning the caller's mount namespace. fsconfig() doesn't repeat that check. It is a WARN_ON() and not a WARN_ON_ONCE(), so the condition can be raised in a loop to taint the kernel and flood the log, and it panics a kernel booted with panic_on_warn. Keep refusing the mount and stop warning about it. ovl_parse_param() already spells a user namespace check this way for Opt_override_creds. Fixes: 1784fbc2ed9c ("ovl: port to new mount api") Cc: stable@vger.kernel.org # v6.5+ Link: https://patch.msgid.link/20260802-work-fill_super-warn-v1-1-4e987911a39a@kernel.org Reviewed-by: Jan Kara Signed-off-by: Christian Brauner (Amutable) Signed-off-by: Greg Kroah-Hartman --- fs/overlayfs/super.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/fs/overlayfs/super.c +++ b/fs/overlayfs/super.c @@ -1381,7 +1381,8 @@ int ovl_fill_super(struct super_block *s int err; err = -EIO; - if (WARN_ON(fc->user_ns != current_user_ns())) + /* The fscontext fd may have been passed to another user namespace. */ + if (fc->user_ns != current_user_ns()) goto out_err; ovl_set_d_op(sb);