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Date: Wed, 16 Sep 2020 09:01:06 +0900 From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp> To: syzbot <syzbot+b38b1ef6edf0c74a8d97@...kaller.appspotmail.com>, george.kennedy@...cle.com, gregkh@...uxfoundation.org, jirislaby@...nel.org, syzkaller-bugs@...glegroups.com Cc: b.zolnierkie@...sung.com, daniel.vetter@...ll.ch, dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org, natechancellor@...il.com Subject: Re: [PATCH] fbcon: Fix user font detection test at fbcon_resize(). Greg, will you pick up this patch? It seems that finding the real cause of [3] and actually fixing [3] will be difficult. Since I can't reproduce [3] locally, I will have to try flood of "#syz test" requests for debug printk() patches. On 2020/09/11 7:57, Tetsuo Handa wrote: > syzbot is reporting OOB read at fbcon_resize() [1], for > commit 39b3cffb8cf31117 ("fbcon: prevent user font height or width change > from causing potential out-of-bounds access") is by error using > registered_fb[con2fb_map[vc->vc_num]]->fbcon_par->p->userfont (which was > set to non-zero) instead of fb_display[vc->vc_num].userfont (which remains > zero for that display). > > We could remove tricky userfont flag [2], for we can determine it by > comparing address of the font data and addresses of built-in font data. > But since that commit is failing to fix the original OOB read [3], this > patch keeps the change minimal in case we decide to revert altogether. > > [1] https://syzkaller.appspot.com/bug?id=ebcbbb6576958a496500fee9cf7aa83ea00b5920 > [2] https://syzkaller.appspot.com/text?tag=Patch&x=14030853900000 > [3] https://syzkaller.appspot.com/bug?id=6fba8c186d97cf1011ab17660e633b1cc4e080c9 > > Reported-by: syzbot <syzbot+b38b1ef6edf0c74a8d97@...kaller.appspotmail.com> > Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp> > Fixes: 39b3cffb8cf31117 ("fbcon: prevent user font height or width change from causing potential out-of-bounds access") > Cc: George Kennedy <george.kennedy@...cle.com> > --- > drivers/video/fbdev/core/fbcon.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c > index 66167830fefd..dae7ae7f225a 100644 > --- a/drivers/video/fbdev/core/fbcon.c > +++ b/drivers/video/fbdev/core/fbcon.c > @@ -2203,7 +2203,7 @@ static int fbcon_resize(struct vc_data *vc, unsigned int width, > struct fb_var_screeninfo var = info->var; > int x_diff, y_diff, virt_w, virt_h, virt_fw, virt_fh; > > - if (ops->p && ops->p->userfont && FNTSIZE(vc->vc_font.data)) { > + if (p->userfont && FNTSIZE(vc->vc_font.data)) { > int size; > int pitch = PITCH(vc->vc_font.width); > >
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