From: Tetsuo Handa penguin-kernel@i-love.sakura.ne.jp
commit 8c28051cdcbe9dfcec6bd0a4709d67a09df6edae upstream.
syzbot is reporting page fault at vga16fb_fillrect() [1], for vga16fb_check_var() is failing to detect multiplication overflow.
if (vxres * vyres > maxmem) { vyres = maxmem / vxres; if (vyres < yres) return -ENOMEM; }
Since no module would accept too huge resolutions where multiplication overflow happens, let's reject in the common path.
Link: https://syzkaller.appspot.com/bug?extid=04168c8063cfdde1db5e [1] Reported-by: syzbot syzbot+04168c8063cfdde1db5e@syzkaller.appspotmail.com Debugged-by: Randy Dunlap rdunlap@infradead.org Signed-off-by: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp Reviewed-by: Geert Uytterhoeven geert+renesas@glider.be Cc: stable@vger.kernel.org Signed-off-by: Daniel Vetter daniel.vetter@ffwll.ch Link: https://patchwork.freedesktop.org/patch/msgid/185175d6-227a-7b55-433d-b07092... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/video/fbdev/core/fbmem.c | 7 +++++++ 1 file changed, 7 insertions(+)
--- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c @@ -34,6 +34,7 @@ #include <linux/fb.h> #include <linux/fbcon.h> #include <linux/mem_encrypt.h> +#include <linux/overflow.h>
#include <asm/fb.h>
@@ -983,6 +984,7 @@ fb_set_var(struct fb_info *info, struct if ((var->activate & FB_ACTIVATE_FORCE) || memcmp(&info->var, var, sizeof(struct fb_var_screeninfo))) { u32 activate = var->activate; + u32 unused;
/* When using FOURCC mode, make sure the red, green, blue and * transp fields are set to 0. @@ -1007,6 +1009,11 @@ fb_set_var(struct fb_info *info, struct if (var->xres < 8 || var->yres < 8) return -EINVAL;
+ /* Too huge resolution causes multiplication overflow. */ + if (check_mul_overflow(var->xres, var->yres, &unused) || + check_mul_overflow(var->xres_virtual, var->yres_virtual, &unused)) + return -EINVAL; + ret = info->fbops->fb_check_var(var, info);
if (ret)