<div dir="ltr">Hello, We would like to report a slab-use-after-free 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. In amdgpu_bo_move, struct ttm_resource *old_mem = bo->resource is assigned. As you can see on the alloc & free stack calls, on the same function amdgpu_bo_move, amdgpu_move_blit in the end frees bo->resource at ttm_bo_move_accel_cleanup with ttm_bo_wait_free_node(bo, man->use_tt). But amdgpu_bo_move continues after that, reaching trace_amdgpu_bo_move(abo, new_mem->mem_type, old_mem->mem_type) at the end, causing the use-after-free bug. Steps to reproduce are as below. union drm_amdgpu_gem_create *arg1; arg1 = malloc(sizeof(union drm_amdgpu_gem_create)); arg1->in.bo_size = 0x8; arg1->in.alignment = 0x0; arg1->in.domains = 0x4; arg1->in.domain_flags = 0x9; ioctl(fd, 0xc0206440, arg1); arg1->in.bo_size = 0x7fffffff; arg1->in.alignment = 0x0; arg1->in.domains = 0x4; arg1->in.domain_flags = 0x9; ioctl(fd, 0xc0206440, arg1); The KASAN report is as follows: ================================================================== BUG: KASAN: slab-use-after-free in amdgpu_bo_move+0x1479/0x1550 Read of size 4 at addr ffff88800f5bee80 by task syz-executor/219 Call Trace: <TASK> amdgpu_bo_move+0x1479/0x1550 ttm_bo_handle_move_mem+0x4d0/0x700 ttm_mem_evict_first+0x945/0x1230 ttm_bo_mem_space+0x6c7/0x940 ttm_bo_validate+0x286/0x650 ttm_bo_init_reserved+0x34c/0x490 amdgpu_bo_create+0x94b/0x1610 amdgpu_bo_create_user+0xa3/0x130 amdgpu_gem_create_ioctl+0x4bc/0xc10 drm_ioctl_kernel+0x300/0x410 drm_ioctl+0x648/0xb30 amdgpu_drm_ioctl+0xc8/0x160 </TASK> Allocated by task 219: kmalloc_trace+0x211/0x390 amdgpu_vram_mgr_new+0x1d6/0xbe0 ttm_resource_alloc+0xfd/0x1e0 ttm_bo_mem_space+0x255/0x940 ttm_bo_validate+0x286/0x650 ttm_bo_init_reserved+0x34c/0x490 amdgpu_bo_create+0x94b/0x1610 amdgpu_bo_create_user+0xa3/0x130 amdgpu_gem_create_ioctl+0x4bc/0xc10 drm_ioctl_kernel+0x300/0x410 drm_ioctl+0x648/0xb30 amdgpu_drm_ioctl+0xc8/0x160 Freed by task 219: kfree+0x111/0x2d0 ttm_resource_free+0x17e/0x1e0 ttm_bo_move_accel_cleanup+0x77e/0x9b0 amdgpu_move_blit+0x3db/0x670 amdgpu_bo_move+0xfa2/0x1550 ttm_bo_handle_move_mem+0x4d0/0x700 ttm_mem_evict_first+0x945/0x1230 ttm_bo_mem_space+0x6c7/0x940 ttm_bo_validate+0x286/0x650 ttm_bo_init_reserved+0x34c/0x490 amdgpu_bo_create+0x94b/0x1610 amdgpu_bo_create_user+0xa3/0x130 amdgpu_gem_create_ioctl+0x4bc/0xc10 drm_ioctl_kernel+0x300/0x410 drm_ioctl+0x648/0xb30 amdgpu_drm_ioctl+0xc8/0x160 The buggy address belongs to the object at ffff88800f5bee70 which belongs to the cache kmalloc-96 of size 96 The buggy address is located 16 bytes inside of freed 96-byte region [ffff88800f5bee70, ffff88800f5beed0) Should you need any more information, please do not hesitate to contact us. Best regards, Joonkyo Jung </div>