[PATCH] drm: drm_bufs: Error out if 'dev->agp' is a null pointer

[Daniel Vetter]

On Mon, Mar 21, 2022 at 09:02:47PM +0800, Zheyu Ma wrote:
> On Thu, Mar 17, 2022 at 6:49 PM Daniel Vetter <daniel at ffwll.ch> wrote:
> >
> > On Fri, Mar 11, 2022 at 07:23:02AM +0000, Zheyu Ma wrote:
> > > The user program can control the 'drm_buf_desc::flags' via ioctl system
> > > call and enter the function drm_legacy_addbufs_agp(). If the driver
> > > doesn't initialize the agp resources, the driver will cause a null
> > > pointer dereference.
> > >
> > > The following log reveals it:
> > >     general protection fault, probably for non-canonical address
> > >     0xdffffc000000000f: 0000 [#1] PREEMPT SMP KASAN PTI
> > >     KASAN: null-ptr-deref in range [0x0000000000000078-0x000000000000007f]
> > >     Call Trace:
> > >      <TASK>
> > >      drm_ioctl_kernel+0x342/0x450 drivers/gpu/drm/drm_ioctl.c:785
> > >      drm_ioctl+0x592/0x940 drivers/gpu/drm/drm_ioctl.c:885
> > >      vfs_ioctl fs/ioctl.c:51 [inline]
> > >      __do_sys_ioctl fs/ioctl.c:874 [inline]
> > >      __se_sys_ioctl+0xaa/0xf0 fs/ioctl.c:860
> > >      do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> > >      do_syscall_64+0x43/0x90 arch/x86/entry/common.c:80
> > >      entry_SYSCALL_64_after_hwframe+0x44/0xae
> > >
> > > Fix this bug by adding a check.
> > >
> > > Signed-off-by: Zheyu Ma <zheyuma97 at gmail.com>
> >
> > You can only hit this if you enabled a DRIVER_LEGACY drm driver, which
> > opens you up to tons of other CVEs and issues. What's your .config?
> 
> Yes, I enable the DRM_LEGACY option in the config.
> I think you mean this is not a normal configuration file? Do you have
> a recommended configuration option for when I want to test the GPU
> driver?

Yeah DRM_LEGACY gives you all kinds of horrible and known-broken
interfaces. Don't enable that :-)

You have a bunch of other drivers enable which require DRM_LEGACY, so
those will disable too. Anything else I think would be an upstream bug and
we'd need to adjust Kconfig (or fix the code).

Cheers, Daniel
> 
> Actually, I use the following configs related to GPU:
> 
> CONFIG_AGP=y
> CONFIG_AGP_AMD64=y
> CONFIG_AGP_INTEL=y
> CONFIG_AGP_SIS=y
> CONFIG_AGP_VIA=y
> CONFIG_INTEL_GTT=y
> CONFIG_VGA_ARB=y
> CONFIG_VGA_ARB_MAX_GPUS=16
> CONFIG_DRM=y
> CONFIG_DRM_MIPI_DSI=y
> CONFIG_DRM_KMS_HELPER=y
> CONFIG_DRM_DEBUG_MODESET_LOCK=y
> CONFIG_DRM_FBDEV_EMULATION=y
> CONFIG_DRM_FBDEV_OVERALLOC=100
> CONFIG_DRM_TTM=y
> CONFIG_DRM_VRAM_HELPER=y
> CONFIG_DRM_TTM_HELPER=y
> CONFIG_DRM_GEM_SHMEM_HELPER=y
> CONFIG_DRM_SCHED=y
> CONFIG_DRM_RADEON=y
> CONFIG_DRM_AMDGPU=y
> CONFIG_DRM_AMD_DC=y
> CONFIG_DRM_AMD_DC_DCN=y
> CONFIG_DRM_I915=y
> CONFIG_DRM_I915_FORCE_PROBE=""
> CONFIG_DRM_I915_CAPTURE_ERROR=y
> CONFIG_DRM_I915_COMPRESS_ERROR=y
> CONFIG_DRM_I915_USERPTR=y
> CONFIG_DRM_I915_REQUEST_TIMEOUT=20000
> CONFIG_DRM_I915_FENCE_TIMEOUT=10000
> CONFIG_DRM_I915_USERFAULT_AUTOSUSPEND=250
> CONFIG_DRM_I915_HEARTBEAT_INTERVAL=2500
> CONFIG_DRM_I915_PREEMPT_TIMEOUT=640
> CONFIG_DRM_I915_MAX_REQUEST_BUSYWAIT=8000
> CONFIG_DRM_I915_STOP_TIMEOUT=100
> CONFIG_DRM_I915_TIMESLICE_DURATION=1
> CONFIG_DRM_VMWGFX=y
> CONFIG_DRM_GMA500=y
> CONFIG_DRM_UDL=y
> CONFIG_DRM_AST=y
> CONFIG_DRM_MGAG200=y
> CONFIG_DRM_QXL=y
> CONFIG_DRM_VIRTIO_GPU=y
> CONFIG_DRM_PANEL=y
> CONFIG_DRM_BRIDGE=y
> CONFIG_DRM_PANEL_BRIDGE=y
> CONFIG_DRM_BOCHS=y
> CONFIG_DRM_CIRRUS_QEMU=y
> CONFIG_DRM_GM12U320=y
> CONFIG_DRM_VBOXVIDEO=y
> CONFIG_DRM_GUD=y
> CONFIG_DRM_HYPERV=y
> CONFIG_DRM_LEGACY=y
> CONFIG_DRM_TDFX=y
> CONFIG_DRM_R128=y
> CONFIG_DRM_MGA=y
> CONFIG_DRM_SIS=y
> CONFIG_DRM_VIA=y
> CONFIG_DRM_SAVAGE=y
> CONFIG_DRM_PANEL_ORIENTATION_QUIRKS=y
> 
> Thanks,
> Zheyu Ma

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch