From: Maciej W. Rozycki macro@orcam.me.uk
commit 3dfac26e2ef29ff2abc2a75aa4cd48fce25a2c4b upstream.
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.
Fixes: 50ec42edd978 ("[PATCH] Detaching fbcon: fix vgacon to allow retaking of the console") Cc: stable@vger.kernel.org # v2.6.18+ Reported-by: Wim Osterholt wim@djo.tudelft.nl Reported-by: Pavel V. Panteleev panteleev_p@mcst.ru Signed-off-by: Maciej W. Rozycki macro@orcam.me.uk Link: https://lore.kernel.org/r/alpine.DEB.2.21.2110252317110.58149@angie.orcam.me... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/video/console/vgacon.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-)
--- a/drivers/video/console/vgacon.c +++ b/drivers/video/console/vgacon.c @@ -365,11 +365,17 @@ 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) { @@ -378,8 +384,6 @@ 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;