KASAN: use-after-free Read in drm_gem_object_release

Fri Jul 10 08:24:03 UTC 2020

I report a bug (in linux-5.8.0-rc4) found by syzkaller.

kernel config: https://github.com/butterflyhack/syzkaller-fuzz/blob/master/v5.8.0-rc4.config

I test the reproducer and crash too.

In the drm_em_vram_t() function,  ttm_bo_init() function call
ttm_bo_init_reserved(),
the ttm_bo_init_reserved() function  call ttm_bo_put(), it will free
gbo->bo that is struct ttm_buffer_object.

then, goto the err_drm_gem_object_release lable,
drm_gem_object_release() function will free gbo->bo.base, so cause use
after free.

crash log:
==================================================================
BUG: KASAN: use-after-free in drm_gem_object_release+0xf7/0x120
drivers/gpu/drm/drm_gem.c:953
Read of size 8 at addr ffff888064dfd928 by task syz-executor.2/1320

CPU: 1 PID: 1320 Comm: syz-executor.2 Not tainted 5.8.0-rc4+ #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.10.2-1ubuntu1 04/01/2014
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x18f/0x20d lib/dump_stack.c:118
 print_address_description.constprop.0.cold+0xae/0x436 mm/kasan/report.c:383
 __kasan_report mm/kasan/report.c:513 [inline]
 kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530
 drm_gem_object_release+0xf7/0x120 drivers/gpu/drm/drm_gem.c:953
 drm_gem_vram_init drivers/gpu/drm/drm_gem_vram_helper.c:211 [inline]
 drm_gem_vram_create+0x3e6/0x5e0 drivers/gpu/drm/drm_gem_vram_helper.c:244
 drm_gem_vram_fill_create_dumb+0x17a/0x310
drivers/gpu/drm/drm_gem_vram_helper.c:615
 drm_gem_vram_driver_dumb_create+0x51/0xb0
drivers/gpu/drm/drm_gem_vram_helper.c:710
 drm_mode_create_dumb+0x27c/0x300 drivers/gpu/drm/drm_dumb_buffers.c:94
 drm_ioctl_kernel+0x220/0x2e0 drivers/gpu/drm/drm_ioctl.c:787
 drm_ioctl+0x4d2/0x96f drivers/gpu/drm/drm_ioctl.c:887
 vfs_ioctl fs/ioctl.c:48 [inline]
 ksys_ioctl+0x11a/0x180 fs/ioctl.c:753
 __do_sys_ioctl fs/ioctl.c:762 [inline]
 __se_sys_ioctl fs/ioctl.c:760 [inline]
 __x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:760
 do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x467a29
Code: Bad RIP value.
RSP: 002b:00007f98f2d40c48 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 000000000076bf00 RCX: 0000000000467a29
RDX: 0000000020000040 RSI: 00000000c02064b2 RDI: 0000000000000003
RBP: 000000000070c600 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f98f2d416bc
R13: 0000000000000297 R14: 0000000000702040 R15: 00000000004d2418

Allocated by task 1320:
 save_stack+0x1b/0x40 mm/kasan/common.c:48
 set_track mm/kasan/common.c:56 [inline]
 __kasan_kmalloc.constprop.0+0xc2/0xd0 mm/kasan/common.c:494
 kmem_cache_alloc_trace+0x14f/0x2d0 mm/slab.c:3551
 kmalloc include/linux/slab.h:555 [inline]
 kzalloc include/linux/slab.h:669 [inline]
 drm_gem_vram_create+0x425/0x5e0 drivers/gpu/drm/drm_gem_vram_helper.c:239
 drm_gem_vram_fill_create_dumb+0x17a/0x310
drivers/gpu/drm/drm_gem_vram_helper.c:615
 drm_gem_vram_driver_dumb_create+0x51/0xb0
drivers/gpu/drm/drm_gem_vram_helper.c:710
 drm_mode_create_dumb+0x27c/0x300 drivers/gpu/drm/drm_dumb_buffers.c:94
 drm_ioctl_kernel+0x220/0x2e0 drivers/gpu/drm/drm_ioctl.c:787
 drm_ioctl+0x4d2/0x96f drivers/gpu/drm/drm_ioctl.c:887
 vfs_ioctl fs/ioctl.c:48 [inline]
 ksys_ioctl+0x11a/0x180 fs/ioctl.c:753
 __do_sys_ioctl fs/ioctl.c:762 [inline]
 __se_sys_ioctl fs/ioctl.c:760 [inline]
 __x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:760
 do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Freed by task 1320:
 save_stack+0x1b/0x40 mm/kasan/common.c:48
 set_track mm/kasan/common.c:56 [inline]
 kasan_set_free_info mm/kasan/common.c:316 [inline]
 __kasan_slab_free+0xf5/0x140 mm/kasan/common.c:455
 __cache_free mm/slab.c:3426 [inline]
 kfree+0x103/0x2c0 mm/slab.c:3757
 ttm_bo_release+0xae1/0x1350 drivers/gpu/drm/ttm/ttm_bo.c:632
 kref_put include/linux/kref.h:65 [inline]
 ttm_bo_put drivers/gpu/drm/ttm/ttm_bo.c:638 [inline]
 ttm_bo_init_reserved+0xb04/0xd00 drivers/gpu/drm/ttm/ttm_bo.c:1339
 ttm_bo_init+0x10e/0x330 drivers/gpu/drm/ttm/ttm_bo.c:1366
 drm_gem_vram_init drivers/gpu/drm/drm_gem_vram_helper.c:202 [inline]
 drm_gem_vram_create+0x3c1/0x5e0 drivers/gpu/drm/drm_gem_vram_helper.c:244
 drm_gem_vram_fill_create_dumb+0x17a/0x310
drivers/gpu/drm/drm_gem_vram_helper.c:615
 drm_gem_vram_driver_dumb_create+0x51/0xb0
drivers/gpu/drm/drm_gem_vram_helper.c:710
 drm_mode_create_dumb+0x27c/0x300 drivers/gpu/drm/drm_dumb_buffers.c:94
 drm_ioctl_kernel+0x220/0x2e0 drivers/gpu/drm/drm_ioctl.c:787
 drm_ioctl+0x4d2/0x96f drivers/gpu/drm/drm_ioctl.c:887
 vfs_ioctl fs/ioctl.c:48 [inline]
 ksys_ioctl+0x11a/0x180 fs/ioctl.c:753
 __do_sys_ioctl fs/ioctl.c:762 [inline]
 __se_sys_ioctl fs/ioctl.c:760 [inline]
 __x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:760
 do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:384
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

The buggy address belongs to the object at ffff888064dfd800
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 296 bytes inside of
 1024-byte region [ffff888064dfd800, ffff888064dfdc00)
The buggy address belongs to the page:
page:ffffea0001937f40 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea0000f3c248 ffffea0001ad7388 ffff88806bc00c40
raw: 0000000000000000 ffff888064dfd000 0000000100000002 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888064dfd800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888064dfd880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888064dfd900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                  ^
 ffff888064dfd980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888064dfda00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Regards,
 butt3rflyh4ck.