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@xxxxxxxxx> 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? -Daniel > --- > drivers/gpu/drm/drm_bufs.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/drm_bufs.c b/drivers/gpu/drm/drm_bufs.c > index fcca21e8efac..4fe2363b1e34 100644 > --- a/drivers/gpu/drm/drm_bufs.c > +++ b/drivers/gpu/drm/drm_bufs.c > @@ -734,7 +734,7 @@ int drm_legacy_addbufs_agp(struct drm_device *dev, > int i, valid; > struct drm_buf **temp_buflist; > > - if (!dma) > + if (!dma || !dev->agp) > return -EINVAL; > > count = request->count; > -- > 2.25.1 > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
