| Message ID | 185175d6-227a-7b55-433d-b070929b262c@i-love.sakura.ne.jp (mailing list archive) |
|---|---|
| State | Accepted, archived |
| Headers | show |
| Series | [v2,(repost)] fbmem: don't allow too huge resolutions | expand |
On Wed, Sep 08, 2021 at 07:27:49PM +0900, Tetsuo Handa wrote: > 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> > --- > Changes in v2: > Use check_mul_overflow(), suggested by Geert Uytterhoeven <geert@linux-m68k.org>. Pushed to drm-misc-next-fixes so it should get into current merge window. I also added a cc: stable here, I htink it's needed. Thanks a lot to both you&Geert for handling this! -Daniel > > drivers/video/fbdev/core/fbmem.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c > index 71fb710f1ce3..7420d2c16e47 100644 > --- a/drivers/video/fbdev/core/fbmem.c > +++ b/drivers/video/fbdev/core/fbmem.c > @@ -962,6 +962,7 @@ fb_set_var(struct fb_info *info, struct fb_var_screeninfo *var) > struct fb_var_screeninfo old_var; > struct fb_videomode mode; > struct fb_event event; > + u32 unused; > > if (var->activate & FB_ACTIVATE_INV_MODE) { > struct fb_videomode mode1, mode2; > @@ -1008,6 +1009,11 @@ fb_set_var(struct fb_info *info, struct fb_var_screeninfo *var) > 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) > -- > 2.18.4 > >
diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c index 71fb710f1ce3..7420d2c16e47 100644 --- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c @@ -962,6 +962,7 @@ fb_set_var(struct fb_info *info, struct fb_var_screeninfo *var) struct fb_var_screeninfo old_var; struct fb_videomode mode; struct fb_event event; + u32 unused; if (var->activate & FB_ACTIVATE_INV_MODE) { struct fb_videomode mode1, mode2; @@ -1008,6 +1009,11 @@ fb_set_var(struct fb_info *info, struct fb_var_screeninfo *var) 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)
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> --- Changes in v2: Use check_mul_overflow(), suggested by Geert Uytterhoeven <geert@linux-m68k.org>. drivers/video/fbdev/core/fbmem.c | 6 ++++++ 1 file changed, 6 insertions(+)