Reporting a use-after-free in amdgpu

[정준교]

Hello,

We would like to report a use-after-free bug in the AMDGPU DRM driver in
the linux kernel 6.2 that we found with our customized Syzkaller.
The bug can be triggered by sending a single amdgpu_gem_userptr_ioctl to
the AMDGPU DRM driver, with invalid addr and size.
We have tested that this bug can still be triggered in the latest RC
kernel, v6.8-rc4.

Steps to reproduce are as below.

struct drm_amdgpu_gem_userptr *arg;
arg = malloc(sizeof(struct drm_amdgpu_gem_userptr));
arg->addr = 0xffffffffffff0000;
arg->size = 0x80000000;
arg->flags = 0x7;
ioctl(AMDGPU_renderD128_DEVICE_FILE, 0xc1186451, arg);

The KASAN report is as follows:
==================================================================
BUG: KASAN: use-after-free in switch_mm_irqs_off+0x89d/0xb70
Read of size 8 at addr ffff88801f17bc00 by task syz-executor/386
Call Trace:
<TASK>
switch_mm_irqs_off+0x89d/0xb70
__schedule+0xa62/0x2630
preempt_schedule_common+0x45/0xd0
vfree+0x4d/0x60
ttm_tt_fini+0xdf/0x1c0
amdgpu_ttm_backend_destroy+0x9f/0xe0
ttm_bo_cleanup_memtype_use+0x142/0x1f0
ttm_bo_release+0x67d/0xc00
ttm_bo_put+0x7c/0xa0
amdgpu_bo_unref+0x3b/0x80
amdgpu_gem_object_free+0x7f/0xc0
drm_gem_object_free+0x5d/0x90
amdgpu_gem_userptr_ioctl+0x452/0x7e0
drm_ioctl_kernel+0x284/0x500
drm_ioctl+0x55e/0xa50
amdgpu_drm_ioctl+0xe3/0x1d0
</TASK>

Allocated by task 385:
kmem_cache_alloc+0x174/0x300
copy_process+0x32d1/0x6640
kernel_clone+0xcd/0x690

Freed by task 386:
kmem_cache_free+0x13b/0x550
mmu_interval_notifier_remove+0x4c8/0x610
amdgpu_hmm_unregister+0x47/0x90
amdgpu_gem_object_free+0x75/0xc0
drm_gem_object_free+0x5d/0x90
amdgpu_gem_userptr_ioctl+0x452/0x7e0
drm_ioctl_kernel+0x284/0x500
drm_ioctl+0x55e/0xa50
amdgpu_drm_ioctl+0xe3/0x1d0

The buggy address belongs to the object at ffff88801f17bb80
which belongs to the cache mm_struct of size 2016
The buggy address is located 128 bytes inside of
2016-byte region [ffff88801f17bb80, ffff88801f17c360)

The buggy address belongs to the physical page:
page:000000002c2a61bd refcount:1 mapcount:0 mapping:0000000000000000
index:0x0 pfn:0x1f178
head:000000002c2a61bd order:3 compound_mapcount:0 subpages_mapcount:0
compound_pincount:0
memcg:ffff8880141aa301
flags: 0x100000000010200(slab|head|node=0|zone=1)
raw: 0100000000010200 ffff88800a44fc80 ffffea00006ca400 dead000000000004
raw: 0000000000000000 00000000800f000f 00000001ffffffff ffff8880141aa301
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88801f17bb00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88801f17bb80: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88801f17bc00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88801f17bc80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88801f17bd00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
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