Hello, We would like to report a null-ptr-deref bug in the AMDGPU DRM driver in the linux kernel v6.8-rc4 that we found with our customized Syzkaller. The bug can be triggered by sending two ioctls to the AMDGPU DRM driver in succession.
The first ioctl amdgpu_ctx_ioctl will create a ctx, and return ctx_id = 1 to the userspace. Second ioctl, actually any ioctl that will eventually call amdgpu_ctx_get_entity, carries this ctx_id and passes the context check. Here, for example, drm_amdgpu_wait_cs. Validations in amdgpu_ctx_get_entity can also be passed by the user-provided values from the ioctl arguments. This eventually leads to drm_sched_entity_init, where the null-ptr-deref will trigger on RCU_INIT_POINTER(entity->last_scheduled, NULL); Steps to reproduce are as below. union drm_amdgpu_ctx *arg1; union drm_amdgpu_wait_cs *arg2; arg1 = malloc(sizeof(union drm_amdgpu_ctx)); arg2 = malloc(sizeof(union drm_amdgpu_wait_cs)); arg1->in.op = 0x1; ioctl(AMDGPU_renderD128_DEVICE_FILE, 0x140106442, arg1); arg2->in.handle = 0x0; arg2->in.timeout = 0x2000000000000; arg2->in.ip_type = 0x9; arg2->in.ip_instance = 0x0; arg2->in.ring = 0x0; arg2->in.ctx_id = 0x1; ioctl(AMDGPU_renderD128_DEVICE_FILE, 0xc0206449, arg2); The KASAN report is as follows: general protection fault, probably for non-canonical address 0xdffffc0000000005: 0000 [#1] PREEMPT SMP KASAN NOPTI KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f] Call Trace: <TASK> ? drm_sched_entity_init+0x16e/0x650 ? drm_sched_entity_init+0x208/0x650 amdgpu_ctx_get_entity+0x944/0xc30 amdgpu_cs_wait_ioctl+0x13d/0x3f0 drm_ioctl_kernel+0x300/0x410 drm_ioctl+0x648/0xb30 amdgpu_drm_ioctl+0xc8/0x160 </TASK> Should you need any more information, please do not hesitate to contact us. Best regards, Joonkyo Jung