Am 08.02.22 um 22:08 schrieb Daniel Vetter:
> Half of it is protected by console_lock, but the other half is a lot
> more awkward: Registration/deregistration of fbdev are serialized, but
> we don't really clear out anything in con2fb_map and so there's
> potential for use-after free mixups.
> 
> First step is to encapsulate the lookup.
> 
> Acked-by: Sam Ravnborg <sam@ravnborg.org>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Helge Deller <deller@gmx.de>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Cc: Du Cheng <ducheng2@gmail.com>
> Cc: Claudio Suarez <cssk@net-c.es>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>

Acked-by: Thomas Zimmermann <tzimmermann@suse.de>

> ---
>   drivers/video/fbdev/core/fbcon.c | 76 ++++++++++++++++++--------------
>   1 file changed, 44 insertions(+), 32 deletions(-)
> 
> diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
> index e925bb608e25..b75e638cb83d 100644
> --- a/drivers/video/fbdev/core/fbcon.c
> +++ b/drivers/video/fbdev/core/fbcon.c
> @@ -110,6 +110,18 @@ static struct fbcon_display fb_display[MAX_NR_CONSOLES];
>   static signed char con2fb_map[MAX_NR_CONSOLES];
>   static signed char con2fb_map_boot[MAX_NR_CONSOLES];
>   
> +static struct fb_info *fbcon_info_from_console(int console)
> +{
> +	WARN_CONSOLE_UNLOCKED();
> +
> +	/*
> +	 * Note that only con2fb_map is protected by the console lock,
> +	 * registered_fb is protected by a separate mutex. This lookup can
> +	 * therefore race.
> +	 */
> +	return registered_fb[con2fb_map[console]];
> +}
> +
>   static int logo_lines;
>   /* logo_shown is an index to vc_cons when >= 0; otherwise follows FBCON_LOGO
>      enums.  */
> @@ -199,7 +211,7 @@ static void fbcon_rotate(struct fb_info *info, u32 rotate)
>   	if (!ops || ops->currcon == -1)
>   		return;
>   
> -	fb_info = registered_fb[con2fb_map[ops->currcon]];
> +	fb_info = fbcon_info_from_console(ops->currcon);
>   
>   	if (info == fb_info) {
>   		struct fbcon_display *p = &fb_display[ops->currcon];
> @@ -226,7 +238,7 @@ static void fbcon_rotate_all(struct fb_info *info, u32 rotate)
>   	for (i = first_fb_vc; i <= last_fb_vc; i++) {
>   		vc = vc_cons[i].d;
>   		if (!vc || vc->vc_mode != KD_TEXT ||
> -		    registered_fb[con2fb_map[i]] != info)
> +		    fbcon_info_from_console(i) != info)
>   			continue;
>   
>   		p = &fb_display[vc->vc_num];
> @@ -356,7 +368,7 @@ static void fb_flashcursor(struct work_struct *work)
>   		vc = vc_cons[ops->currcon].d;
>   
>   	if (!vc || !con_is_visible(vc) ||
> - 	    registered_fb[con2fb_map[vc->vc_num]] != info ||
> +	    fbcon_info_from_console(vc->vc_num) != info ||
>   	    vc->vc_deccm != 1) {
>   		console_unlock();
>   		return;
> @@ -791,7 +803,7 @@ static void con2fb_init_display(struct vc_data *vc, struct fb_info *info,
>   	if (show_logo) {
>   		struct vc_data *fg_vc = vc_cons[fg_console].d;
>   		struct fb_info *fg_info =
> -			registered_fb[con2fb_map[fg_console]];
> +			fbcon_info_from_console(fg_console);
>   
>   		fbcon_prepare_logo(fg_vc, fg_info, fg_vc->vc_cols,
>   				   fg_vc->vc_rows, fg_vc->vc_cols,
> @@ -1014,7 +1026,7 @@ static void fbcon_init(struct vc_data *vc, int init)
>   	if (con2fb_map[vc->vc_num] == -1)
>   		con2fb_map[vc->vc_num] = info_idx;
>   
> -	info = registered_fb[con2fb_map[vc->vc_num]];
> +	info = fbcon_info_from_console(vc->vc_num);
>   
>   	if (logo_shown < 0 && console_loglevel <= CONSOLE_LOGLEVEL_QUIET)
>   		logo_shown = FBCON_LOGO_DONTSHOW;
> @@ -1231,7 +1243,7 @@ static void fbcon_deinit(struct vc_data *vc)
>   static void fbcon_clear(struct vc_data *vc, int sy, int sx, int height,
>   			int width)
>   {
> -	struct fb_info *info = registered_fb[con2fb_map[vc->vc_num]];
> +	struct fb_info *info = fbcon_info_from_console(vc->vc_num);
>   	struct fbcon_ops *ops = info->fbcon_par;
>   
>   	struct fbcon_display *p = &fb_display[vc->vc_num];
> @@ -1269,7 +1281,7 @@ static void fbcon_clear(struct vc_data *vc, int sy, int sx, int height,
>   static void fbcon_putcs(struct vc_data *vc, const unsigned short *s,
>   			int count, int ypos, int xpos)
>   {
> -	struct fb_info *info = registered_fb[con2fb_map[vc->vc_num]];
> +	struct fb_info *info = fbcon_info_from_console(vc->vc_num);
>   	struct fbcon_display *p = &fb_display[vc->vc_num];
>   	struct fbcon_ops *ops = info->fbcon_par;
>   
> @@ -1289,7 +1301,7 @@ static void fbcon_putc(struct vc_data *vc, int c, int ypos, int xpos)
>   
>   static void fbcon_clear_margins(struct vc_data *vc, int bottom_only)
>   {
> -	struct fb_info *info = registered_fb[con2fb_map[vc->vc_num]];
> +	struct fb_info *info = fbcon_info_from_console(vc->vc_num);
>   	struct fbcon_ops *ops = info->fbcon_par;
>   
>   	if (!fbcon_is_inactive(vc, info))
> @@ -1298,7 +1310,7 @@ static void fbcon_clear_margins(struct vc_data *vc, int bottom_only)
>   
>   static void fbcon_cursor(struct vc_data *vc, int mode)
>   {
> -	struct fb_info *info = registered_fb[con2fb_map[vc->vc_num]];
> +	struct fb_info *info = fbcon_info_from_console(vc->vc_num);
>   	struct fbcon_ops *ops = info->fbcon_par;
>    	int c = scr_readw((u16 *) vc->vc_pos);
>   
> @@ -1392,7 +1404,7 @@ static void fbcon_set_disp(struct fb_info *info, struct fb_var_screeninfo *var,
>   
>   static __inline__ void ywrap_up(struct vc_data *vc, int count)
>   {
> -	struct fb_info *info = registered_fb[con2fb_map[vc->vc_num]];
> +	struct fb_info *info = fbcon_info_from_console(vc->vc_num);
>   	struct fbcon_ops *ops = info->fbcon_par;
>   	struct fbcon_display *p = &fb_display[vc->vc_num];
>   
> @@ -1411,7 +1423,7 @@ static __inline__ void ywrap_up(struct vc_data *vc, int count)
>   
>   static __inline__ void ywrap_down(struct vc_data *vc, int count)
>   {
> -	struct fb_info *info = registered_fb[con2fb_map[vc->vc_num]];
> +	struct fb_info *info = fbcon_info_from_console(vc->vc_num);
>   	struct fbcon_ops *ops = info->fbcon_par;
>   	struct fbcon_display *p = &fb_display[vc->vc_num];
>   
> @@ -1430,7 +1442,7 @@ static __inline__ void ywrap_down(struct vc_data *vc, int count)
>   
>   static __inline__ void ypan_up(struct vc_data *vc, int count)
>   {
> -	struct fb_info *info = registered_fb[con2fb_map[vc->vc_num]];
> +	struct fb_info *info = fbcon_info_from_console(vc->vc_num);
>   	struct fbcon_display *p = &fb_display[vc->vc_num];
>   	struct fbcon_ops *ops = info->fbcon_par;
>   
> @@ -1454,7 +1466,7 @@ static __inline__ void ypan_up(struct vc_data *vc, int count)
>   
>   static __inline__ void ypan_up_redraw(struct vc_data *vc, int t, int count)
>   {
> -	struct fb_info *info = registered_fb[con2fb_map[vc->vc_num]];
> +	struct fb_info *info = fbcon_info_from_console(vc->vc_num);
>   	struct fbcon_ops *ops = info->fbcon_par;
>   	struct fbcon_display *p = &fb_display[vc->vc_num];
>   
> @@ -1478,7 +1490,7 @@ static __inline__ void ypan_up_redraw(struct vc_data *vc, int t, int count)
>   
>   static __inline__ void ypan_down(struct vc_data *vc, int count)
>   {
> -	struct fb_info *info = registered_fb[con2fb_map[vc->vc_num]];
> +	struct fb_info *info = fbcon_info_from_console(vc->vc_num);
>   	struct fbcon_display *p = &fb_display[vc->vc_num];
>   	struct fbcon_ops *ops = info->fbcon_par;
>   
> @@ -1502,7 +1514,7 @@ static __inline__ void ypan_down(struct vc_data *vc, int count)
>   
>   static __inline__ void ypan_down_redraw(struct vc_data *vc, int t, int count)
>   {
> -	struct fb_info *info = registered_fb[con2fb_map[vc->vc_num]];
> +	struct fb_info *info = fbcon_info_from_console(vc->vc_num);
>   	struct fbcon_ops *ops = info->fbcon_par;
>   	struct fbcon_display *p = &fb_display[vc->vc_num];
>   
> @@ -1666,7 +1678,7 @@ static void fbcon_redraw(struct vc_data *vc, struct fbcon_display *p,
>   static void fbcon_bmove_rec(struct vc_data *vc, struct fbcon_display *p, int sy, int sx,
>   			    int dy, int dx, int height, int width, u_int y_break)
>   {
> -	struct fb_info *info = registered_fb[con2fb_map[vc->vc_num]];
> +	struct fb_info *info = fbcon_info_from_console(vc->vc_num);
>   	struct fbcon_ops *ops = info->fbcon_par;
>   	u_int b;
>   
> @@ -1708,7 +1720,7 @@ static void fbcon_bmove_rec(struct vc_data *vc, struct fbcon_display *p, int sy,
>   static void fbcon_bmove(struct vc_data *vc, int sy, int sx, int dy, int dx,
>   			int height, int width)
>   {
> -	struct fb_info *info = registered_fb[con2fb_map[vc->vc_num]];
> +	struct fb_info *info = fbcon_info_from_console(vc->vc_num);
>   	struct fbcon_display *p = &fb_display[vc->vc_num];
>   
>   	if (fbcon_is_inactive(vc, info))
> @@ -1731,7 +1743,7 @@ static void fbcon_bmove(struct vc_data *vc, int sy, int sx, int dy, int dx,
>   static bool fbcon_scroll(struct vc_data *vc, unsigned int t, unsigned int b,
>   		enum con_scroll dir, unsigned int count)
>   {
> -	struct fb_info *info = registered_fb[con2fb_map[vc->vc_num]];
> +	struct fb_info *info = fbcon_info_from_console(vc->vc_num);
>   	struct fbcon_display *p = &fb_display[vc->vc_num];
>   	int scroll_partial = info->flags & FBINFO_PARTIAL_PAN_OK;
>   
> @@ -1996,7 +2008,7 @@ static void updatescrollmode(struct fbcon_display *p,
>   static int fbcon_resize(struct vc_data *vc, unsigned int width,
>   			unsigned int height, unsigned int user)
>   {
> -	struct fb_info *info = registered_fb[con2fb_map[vc->vc_num]];
> +	struct fb_info *info = fbcon_info_from_console(vc->vc_num);
>   	struct fbcon_ops *ops = info->fbcon_par;
>   	struct fbcon_display *p = &fb_display[vc->vc_num];
>   	struct fb_var_screeninfo var = info->var;
> @@ -2065,7 +2077,7 @@ static int fbcon_switch(struct vc_data *vc)
>   	struct fb_var_screeninfo var;
>   	int i, ret, prev_console;
>   
> -	info = registered_fb[con2fb_map[vc->vc_num]];
> +	info = fbcon_info_from_console(vc->vc_num);
>   	ops = info->fbcon_par;
>   
>   	if (logo_shown >= 0) {
> @@ -2079,7 +2091,7 @@ static int fbcon_switch(struct vc_data *vc)
>   
>   	prev_console = ops->currcon;
>   	if (prev_console != -1)
> -		old_info = registered_fb[con2fb_map[prev_console]];
> +		old_info = fbcon_info_from_console(prev_console);
>   	/*
>   	 * FIXME: If we have multiple fbdev's loaded, we need to
>   	 * update all info->currcon.  Perhaps, we can place this
> @@ -2202,7 +2214,7 @@ static void fbcon_generic_blank(struct vc_data *vc, struct fb_info *info,
>   
>   static int fbcon_blank(struct vc_data *vc, int blank, int mode_switch)
>   {
> -	struct fb_info *info = registered_fb[con2fb_map[vc->vc_num]];
> +	struct fb_info *info = fbcon_info_from_console(vc->vc_num);
>   	struct fbcon_ops *ops = info->fbcon_par;
>   
>   	if (mode_switch) {
> @@ -2244,7 +2256,7 @@ static int fbcon_blank(struct vc_data *vc, int blank, int mode_switch)
>   
>   static int fbcon_debug_enter(struct vc_data *vc)
>   {
> -	struct fb_info *info = registered_fb[con2fb_map[vc->vc_num]];
> +	struct fb_info *info = fbcon_info_from_console(vc->vc_num);
>   	struct fbcon_ops *ops = info->fbcon_par;
>   
>   	ops->save_graphics = ops->graphics;
> @@ -2257,7 +2269,7 @@ static int fbcon_debug_enter(struct vc_data *vc)
>   
>   static int fbcon_debug_leave(struct vc_data *vc)
>   {
> -	struct fb_info *info = registered_fb[con2fb_map[vc->vc_num]];
> +	struct fb_info *info = fbcon_info_from_console(vc->vc_num);
>   	struct fbcon_ops *ops = info->fbcon_par;
>   
>   	ops->graphics = ops->save_graphics;
> @@ -2393,7 +2405,7 @@ static void set_vc_hi_font(struct vc_data *vc, bool set)
>   static int fbcon_do_set_font(struct vc_data *vc, int w, int h, int charcount,
>   			     const u8 * data, int userfont)
>   {
> -	struct fb_info *info = registered_fb[con2fb_map[vc->vc_num]];
> +	struct fb_info *info = fbcon_info_from_console(vc->vc_num);
>   	struct fbcon_ops *ops = info->fbcon_par;
>   	struct fbcon_display *p = &fb_display[vc->vc_num];
>   	int resize;
> @@ -2447,7 +2459,7 @@ static int fbcon_do_set_font(struct vc_data *vc, int w, int h, int charcount,
>   static int fbcon_set_font(struct vc_data *vc, struct console_font *font,
>   			  unsigned int flags)
>   {
> -	struct fb_info *info = registered_fb[con2fb_map[vc->vc_num]];
> +	struct fb_info *info = fbcon_info_from_console(vc->vc_num);
>   	unsigned charcount = font->charcount;
>   	int w = font->width;
>   	int h = font->height;
> @@ -2511,7 +2523,7 @@ static int fbcon_set_font(struct vc_data *vc, struct console_font *font,
>   
>   static int fbcon_set_def_font(struct vc_data *vc, struct console_font *font, char *name)
>   {
> -	struct fb_info *info = registered_fb[con2fb_map[vc->vc_num]];
> +	struct fb_info *info = fbcon_info_from_console(vc->vc_num);
>   	const struct font_desc *f;
>   
>   	if (!name)
> @@ -2535,7 +2547,7 @@ static struct fb_cmap palette_cmap = {
>   
>   static void fbcon_set_palette(struct vc_data *vc, const unsigned char *table)
>   {
> -	struct fb_info *info = registered_fb[con2fb_map[vc->vc_num]];
> +	struct fb_info *info = fbcon_info_from_console(vc->vc_num);
>   	int i, j, k, depth;
>   	u8 val;
>   
> @@ -2651,7 +2663,7 @@ static void fbcon_modechanged(struct fb_info *info)
>   		return;
>   	vc = vc_cons[ops->currcon].d;
>   	if (vc->vc_mode != KD_TEXT ||
> -	    registered_fb[con2fb_map[ops->currcon]] != info)
> +	    fbcon_info_from_console(ops->currcon) != info)
>   		return;
>   
>   	p = &fb_display[vc->vc_num];
> @@ -2691,7 +2703,7 @@ static void fbcon_set_all_vcs(struct fb_info *info)
>   	for (i = first_fb_vc; i <= last_fb_vc; i++) {
>   		vc = vc_cons[i].d;
>   		if (!vc || vc->vc_mode != KD_TEXT ||
> -		    registered_fb[con2fb_map[i]] != info)
> +		    fbcon_info_from_console(i) != info)
>   			continue;
>   
>   		if (con_is_visible(vc)) {
> @@ -2954,7 +2966,7 @@ void fbcon_fb_blanked(struct fb_info *info, int blank)
>   
>   	vc = vc_cons[ops->currcon].d;
>   	if (vc->vc_mode != KD_TEXT ||
> -			registered_fb[con2fb_map[ops->currcon]] != info)
> +			fbcon_info_from_console(ops->currcon) != info)
>   		return;
>   
>   	if (con_is_visible(vc)) {
> @@ -2974,7 +2986,7 @@ void fbcon_new_modelist(struct fb_info *info)
>   	const struct fb_videomode *mode;
>   
>   	for (i = first_fb_vc; i <= last_fb_vc; i++) {
> -		if (registered_fb[con2fb_map[i]] != info)
> +		if (fbcon_info_from_console(i) != info)
>   			continue;
>   		if (!fb_display[i].mode)
>   			continue;

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev