On Thu, Sep 2, 2021 at 9:15 PM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote: > > Hi Dongliang, > > On Thu, Sep 2, 2021 at 8:04 AM Dongliang Mu <mudongliangabcd@xxxxxxxxx> wrote: > > [ Upstream commit a49145acfb975d921464b84fe00279f99827d816 ] > > Oops, looks like I missed when that one was submitted for review... This patch cannot directly apply to old stable trees. Maybe that's the reason. > > > A fb_ioctl() FBIOPUT_VSCREENINFO call with invalid xres setting > > or yres setting in struct fb_var_screeninfo will result in a > > KASAN: vmalloc-out-of-bounds failure in bitfill_aligned() as > > the margins are being cleared. The margins are cleared in > > chunks and if the xres setting or yres setting is a value of > > zero upto the chunk size, the failure will occur. > > > > Add a margin check to validate xres and yres settings. > > Shouldn't (the caller of) bitfill_aligned() be fixed instead? > Can this be triggered by e.g. using the mini_4x6 font? I am sorry. I don't know much detail about this subsystem. I just found syzkaller can still trigger this bug in linux-4.19. Combined with the bug information, I found this patch is not merged into the old kernel trees. So I send this patch rebased on linux-4.19. Also I have tested it on linux-4.14 and below. > > > Note that, this patch needs special handling to backport it to linux > > kernel 4.19, 4.14, 4.9, 4.4. > > > > Signed-off-by: George Kennedy <george.kennedy@xxxxxxxxxx> > > Reported-by: syzbot+e5fd3e65515b48c02a30@xxxxxxxxxxxxxxxxxxxxxxxxx > > Reviewed-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx> > > Cc: Dhaval Giani <dhaval.giani@xxxxxxxxxx> > > Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx> > > Link: https://patchwork.freedesktop.org/patch/msgid/1594149963-13801-1-git-send-email-george.kennedy@xxxxxxxxxx > > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> > > --- > > drivers/video/fbdev/core/fbmem.c | 4 ++++ > > 1 file changed, 4 insertions(+) > > > > diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c > > index 84845275dbef..de04c097d67c 100644 > > --- a/drivers/video/fbdev/core/fbmem.c > > +++ b/drivers/video/fbdev/core/fbmem.c > > @@ -991,6 +991,10 @@ fb_set_var(struct fb_info *info, struct fb_var_screeninfo *var) > > goto done; > > } > > > > + /* bitfill_aligned() assumes that it's at least 8x8 */ > > + if (var->xres < 8 || var->yres < 8) > > + return -EINVAL; > > Are you sure there don't exist such small displays (e.g. OLED)? > > > + > > ret = info->fbops->fb_check_var(var, info); > > > > if (ret) > > Gr{oetje,eeting}s, > > Geert > > -- > Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx > > In personal conversations with technical people, I call myself a hacker. But > when I'm talking to journalists I just say "programmer" or something like that. > -- Linus Torvalds
