From patchwork Mon Oct 25 22:26:22 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Maciej W. Rozycki" X-Patchwork-Id: 12583087 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 71637C433F5 for ; Mon, 25 Oct 2021 22:26:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5B2DE61039 for ; Mon, 25 Oct 2021 22:26:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234033AbhJYW2x (ORCPT ); Mon, 25 Oct 2021 18:28:53 -0400 Received: from angie.orcam.me.uk ([78.133.224.34]:34528 "EHLO angie.orcam.me.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233692AbhJYW2v (ORCPT ); Mon, 25 Oct 2021 18:28:51 -0400 Received: by angie.orcam.me.uk (Postfix, from userid 500) id 3C03492009C; Tue, 26 Oct 2021 00:26:22 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by angie.orcam.me.uk (Postfix) with ESMTP id 378FE92009B; Tue, 26 Oct 2021 00:26:22 +0200 (CEST) Date: Tue, 26 Oct 2021 00:26:22 +0200 (CEST) From: "Maciej W. Rozycki" To: Greg Kroah-Hartman cc: Wim Osterholt , "Pavel V. Panteleev" , dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] vgacon: Propagate console boot parameters before calling `vc_resize' Message-ID: User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-fbdev@vger.kernel.org Fix a division by zero in `vgacon_resize' with a backtrace like: vgacon_resize vc_do_resize vgacon_init do_bind_con_driver do_unbind_con_driver fbcon_fb_unbind do_unregister_framebuffer do_register_framebuffer register_framebuffer __drm_fb_helper_initial_config_and_unlock drm_helper_hpd_irq_event dw_hdmi_irq irq_thread kthread caused by `c->vc_cell_height' not having been initialized. This has only started to trigger with commit 860dafa90259 ("vt: Fix character height handling with VT_RESIZEX"), however the ultimate offender is commit 50ec42edd978 ("[PATCH] Detaching fbcon: fix vgacon to allow retaking of the console"). Said commit has added a call to `vc_resize' whenever `vgacon_init' is called with the `init' argument set to 0, which did not happen before. And the call is made before a key vgacon boot parameter retrieved in `vgacon_startup' has been propagated in `vgacon_init' for `vc_resize' to use to the console structure being worked on. Previously the parameter was `c->vc_font.height' and now it is `c->vc_cell_height'. In this particular scenario the registration of fbcon has failed and vt resorts to vgacon. Now fbcon does have initialized `c->vc_font.height' somehow, unlike `c->vc_cell_height', which is why this code did not crash before, but either way the boot parameters should have been copied to the console structure ahead of the call to `vc_resize' rather than afterwards, so that first the call has a chance to use them and second they do not change the console structure to something possibly different from what was used by `vc_resize'. Move the propagation of the vgacon boot parameters ahead of the call to `vc_resize' then. Adjust the comment accordingly. Signed-off-by: Maciej W. Rozycki Reported-by: Wim Osterholt Reported-by: Pavel V. Panteleev Fixes: 50ec42edd978 ("[PATCH] Detaching fbcon: fix vgacon to allow retaking of the console") Cc: stable@vger.kernel.org # v2.6.18+ --- drivers/video/console/vgacon.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) linux-vt-vgacon-init-cell-height-fix.diff Index: linux-macro-ide-tty/drivers/video/console/vgacon.c =================================================================== --- linux-macro-ide-tty.orig/drivers/video/console/vgacon.c +++ linux-macro-ide-tty/drivers/video/console/vgacon.c @@ -366,11 +366,17 @@ static void vgacon_init(struct vc_data * struct uni_pagedir *p; /* - * We cannot be loaded as a module, therefore init is always 1, - * but vgacon_init can be called more than once, and init will - * not be 1. + * We cannot be loaded as a module, therefore init will be 1 + * if we are the default console, however if we are a fallback + * console, for example if fbcon has failed registration, then + * init will be 0, so we need to make sure our boot parameters + * have been copied to the console structure for vgacon_resize + * ultimately called by vc_resize. Any subsequent calls to + * vgacon_init init will have init set to 0 too. */ c->vc_can_do_color = vga_can_do_color; + c->vc_scan_lines = vga_scan_lines; + c->vc_font.height = c->vc_cell_height = vga_video_font_height; /* set dimensions manually if init != 0 since vc_resize() will fail */ if (init) { @@ -379,8 +385,6 @@ static void vgacon_init(struct vc_data * } else vc_resize(c, vga_video_num_columns, vga_video_num_lines); - c->vc_scan_lines = vga_scan_lines; - c->vc_font.height = c->vc_cell_height = vga_video_font_height; c->vc_complement_mask = 0x7700; if (vga_512_chars) c->vc_hi_font_mask = 0x0800;