On Thu, Oct 28, 2021 at 08:57:17AM -0500, George Kennedy wrote: > Do a sanity check on struct drm_format_info hsub and vsub values to > avoid divide by zero. > > Syzkaller reported a divide error in framebuffer_check() when the > DRM_FORMAT_Q410 or DRM_FORMAT_Q401 pixel_format is passed in via > the DRM_IOCTL_MODE_ADDFB2 ioctl. The drm_format_info struct for > the DRM_FORMAT_Q410 pixel_pattern has ".hsub = 0" and ".vsub = 0". > fb_plane_width() uses hsub as a divisor and fb_plane_height() uses > vsub as a divisor. These divisors need to be sanity checked for > zero before use. > > divide error: 0000 [#1] SMP KASAN NOPTI > CPU: 0 PID: 14995 Comm: syz-executor709 Not tainted 5.15.0-rc6-syzk #1 > Hardware name: Red Hat KVM, BIOS 1.13.0-2 > RIP: 0010:framebuffer_check drivers/gpu/drm/drm_framebuffer.c:199 [inline] > RIP: 0010:drm_internal_framebuffer_create+0x604/0xf90 > drivers/gpu/drm/drm_framebuffer.c:317 > > Call Trace: > drm_mode_addfb2+0xdc/0x320 drivers/gpu/drm/drm_framebuffer.c:355 > drm_mode_addfb2_ioctl+0x2a/0x40 drivers/gpu/drm/drm_framebuffer.c:391 > drm_ioctl_kernel+0x23a/0x2e0 drivers/gpu/drm/drm_ioctl.c:795 > drm_ioctl+0x589/0xac0 drivers/gpu/drm/drm_ioctl.c:898 > vfs_ioctl fs/ioctl.c:51 [inline] > __do_sys_ioctl fs/ioctl.c:874 [inline] > __se_sys_ioctl fs/ioctl.c:860 [inline] > __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860 > do_syscall_x64 arch/x86/entry/common.c:50 [inline] > do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80 > entry_SYSCALL_64_after_hwframe+0x44/0xae > > Signed-off-by: George Kennedy <george.kennedy@xxxxxxxxxx> > --- > drivers/gpu/drm/drm_framebuffer.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/drivers/gpu/drm/drm_framebuffer.c b/drivers/gpu/drm/drm_framebuffer.c > index 07f5abc..a146e4b 100644 > --- a/drivers/gpu/drm/drm_framebuffer.c > +++ b/drivers/gpu/drm/drm_framebuffer.c > @@ -195,6 +195,16 @@ static int framebuffer_check(struct drm_device *dev, > /* now let the driver pick its own format info */ > info = drm_get_format_info(dev, r); > > + if (info->hsub == 0) { > + DRM_DEBUG_KMS("bad horizontal chroma subsampling factor %u\n", info->hsub); > + return -EINVAL; > + } > + > + if (info->vsub == 0) { > + DRM_DEBUG_KMS("bad vertical chroma subsampling factor %u\n", info->vsub); > + return -EINVAL; > + } Looks like duct tape to me. I think we need to either fix those formats to have valid format info, or just revert the whole patch that added such broken things. > + > for (i = 0; i < info->num_planes; i++) { > unsigned int width = fb_plane_width(r->width, info, i); > unsigned int height = fb_plane_height(r->height, info, i); > -- > 1.8.3.1 -- Ville Syrjälä Intel