From af0db3c1f898144846d4c172531a199bb3ca375d Mon Sep 17 00:00:00 2001 From: Sravan Kumar Gundu Date: Thu, 31 Jul 2025 15:36:18 -0500 Subject: [PATCH 1/2] fbdev: Fix vmalloc out-of-bounds write in fast_imageblit This issue triggers when a userspace program does an ioctl FBIOPUT_CON2FBMAP by passing console number and frame buffer number. Ideally this maps console to frame buffer and updates the screen if console is visible. As part of mapping it has to do resize of console according to frame buffer info. if this resize fails and returns from vc_do_resize() and continues further. At this point console and new frame buffer are mapped and sets display vars. Despite failure still it continue to proceed updating the screen at later stages where vc_data is related to previous frame buffer and frame buffer info and display vars are mapped to new frame buffer and eventully leading to out-of-bounds write in fast_imageblit(). This bheviour is excepted only when fg_console is equal to requested console which is a visible console and updates screen with invalid struct references in fbcon_putcs(). Reported-and-tested-by: syzbot+c4b7aa0513823e2ea880@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=c4b7aa0513823e2ea880 Signed-off-by: Sravan Kumar Gundu Cc: stable@vger.kernel.org Signed-off-by: Helge Deller --- drivers/video/fbdev/core/fbcon.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c index 2df48037688d..e71629618e6a 100644 --- a/drivers/video/fbdev/core/fbcon.c +++ b/drivers/video/fbdev/core/fbcon.c @@ -825,7 +825,8 @@ static void con2fb_init_display(struct vc_data *vc, struct fb_info *info, fg_vc->vc_rows); } - update_screen(vc_cons[fg_console].d); + if (fg_console != unit) + update_screen(vc_cons[fg_console].d); } /** @@ -1362,6 +1363,7 @@ static void fbcon_set_disp(struct fb_info *info, struct fb_var_screeninfo *var, struct vc_data *svc; struct fbcon_ops *ops = info->fbcon_par; int rows, cols; + unsigned long ret = 0; p = &fb_display[unit]; @@ -1412,11 +1414,10 @@ static void fbcon_set_disp(struct fb_info *info, struct fb_var_screeninfo *var, rows = FBCON_SWAP(ops->rotate, info->var.yres, info->var.xres); cols /= vc->vc_font.width; rows /= vc->vc_font.height; - vc_resize(vc, cols, rows); + ret = vc_resize(vc, cols, rows); - if (con_is_visible(vc)) { + if (con_is_visible(vc) && !ret) update_screen(vc); - } } static __inline__ void ywrap_up(struct vc_data *vc, int count) From e4fc307d8e24f122402907ebf585248cad52841d Mon Sep 17 00:00:00 2001 From: Helge Deller Date: Sat, 2 Aug 2025 21:34:37 +0200 Subject: [PATCH 2/2] Revert "vgacon: Add check for vc_origin address range in vgacon_scroll()" This reverts commit 864f9963ec6b4b76d104d595ba28110b87158003. The patch is wrong as it checks vc_origin against vc_screenbuf, while in text mode it should compare against vga_vram_base. As such it broke VGA text scrolling, which can be reproduced like this: (1) boot a kernel that is configured to use text mode VGA-console (2) type commands: ls -l /usr/bin | less -S (3) scroll up/down with cursor-down/up keys Reported-by: Jari Ruusu Cc: stable@vger.kernel.org Cc: Yi Yang Cc: GONG Ruiqi Signed-off-by: Helge Deller --- drivers/video/console/vgacon.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c index f9cdbf8c53e3..37bd18730fe0 100644 --- a/drivers/video/console/vgacon.c +++ b/drivers/video/console/vgacon.c @@ -1168,7 +1168,7 @@ static bool vgacon_scroll(struct vc_data *c, unsigned int t, unsigned int b, c->vc_screenbuf_size - delta); c->vc_origin = vga_vram_end - c->vc_screenbuf_size; vga_rolled_over = 0; - } else if (oldo - delta >= (unsigned long)c->vc_screenbuf) + } else c->vc_origin -= delta; c->vc_scr_end = c->vc_origin + c->vc_screenbuf_size; scr_memsetw((u16 *) (c->vc_origin), c->vc_video_erase_char,