==================================================================
BUG: KASAN: use-after-free in vgem_gem_dumb_create+0x200/0x210 drivers/gpu/drm/vgem/vgem_drv.c:215
Read of size 8 at addr ffff8880a9669680 by task syz-executor.0/20537

CPU: 0 PID: 20537 Comm: syz-executor.0 Not tainted 4.14.275-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x1b2/0x281 lib/dump_stack.c:58
 print_address_description.cold+0x54/0x1d3 mm/kasan/report.c:252
 kasan_report_error.cold+0x8a/0x191 mm/kasan/report.c:351
 kasan_report mm/kasan/report.c:409 [inline]
 __asan_report_load8_noabort+0x68/0x70 mm/kasan/report.c:430
 vgem_gem_dumb_create+0x200/0x210 drivers/gpu/drm/vgem/vgem_drv.c:215
 drm_mode_create_dumb_ioctl+0x221/0x2b0 drivers/gpu/drm/drm_dumb_buffers.c:92
 drm_ioctl_kernel+0x14c/0x200 drivers/gpu/drm/drm_ioctl.c:737
 drm_ioctl+0x42e/0x890 drivers/gpu/drm/drm_ioctl.c:840
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x75a/0xff0 fs/ioctl.c:684
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x7f/0xb0 fs/ioctl.c:692
 do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x7febafe24049
RSP: 002b:00007febae778168 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007febaff37030 RCX: 00007febafe24049
RDX: 0000000020000040 RSI: 00000000c02064b2 RDI: 0000000000000003
RBP: 00007febafe7e08d R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fff49033c3f R14: 00007febae778300 R15: 0000000000022000

Allocated by task 20537:
 save_stack mm/kasan/kasan.c:447 [inline]
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc+0xeb/0x160 mm/kasan/kasan.c:551
 kmem_cache_alloc_trace+0x131/0x3d0 mm/slab.c:3618
 kmalloc include/linux/slab.h:488 [inline]
 kzalloc include/linux/slab.h:661 [inline]
 __vgem_gem_create+0x44/0xe0 drivers/gpu/drm/vgem/vgem_drv.c:159
 vgem_gem_create drivers/gpu/drm/vgem/vgem_drv.c:188 [inline]
 vgem_gem_dumb_create+0xc5/0x210 drivers/gpu/drm/vgem/vgem_drv.c:211
 drm_mode_create_dumb_ioctl+0x221/0x2b0 drivers/gpu/drm/drm_dumb_buffers.c:92
 drm_ioctl_kernel+0x14c/0x200 drivers/gpu/drm/drm_ioctl.c:737
 drm_ioctl+0x42e/0x890 drivers/gpu/drm/drm_ioctl.c:840
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x75a/0xff0 fs/ioctl.c:684
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x7f/0xb0 fs/ioctl.c:692
 do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x46/0xbb

Freed by task 20537:
 save_stack mm/kasan/kasan.c:447 [inline]
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0xc3/0x1a0 mm/kasan/kasan.c:524
 __cache_free mm/slab.c:3496 [inline]
 kfree+0xc9/0x250 mm/slab.c:3815
 drm_gem_object_free+0x8f/0x150 drivers/gpu/drm/drm_gem.c:836
 kref_put include/linux/kref.h:70 [inline]
 drm_gem_object_put_unlocked+0xc3/0x160 drivers/gpu/drm/drm_gem.c:865
 vgem_gem_create drivers/gpu/drm/vgem/vgem_drv.c:193 [inline]
 vgem_gem_dumb_create+0xf2/0x210 drivers/gpu/drm/vgem/vgem_drv.c:211
 drm_mode_create_dumb_ioctl+0x221/0x2b0 drivers/gpu/drm/drm_dumb_buffers.c:92
 drm_ioctl_kernel+0x14c/0x200 drivers/gpu/drm/drm_ioctl.c:737
 drm_ioctl+0x42e/0x890 drivers/gpu/drm/drm_ioctl.c:840
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x75a/0xff0 fs/ioctl.c:684
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x7f/0xb0 fs/ioctl.c:692
 do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x46/0xbb

The buggy address belongs to the object at ffff8880a9669580
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 256 bytes inside of
 512-byte region [ffff8880a9669580, ffff8880a9669780)
The buggy address belongs to the page:
page:ffffea0002a59a40 count:1 mapcount:0 mapping:ffff8880a9669080 index:0xffff8880a9669800
flags: 0xfff00000000100(slab)
raw: 00fff00000000100 ffff8880a9669080 ffff8880a9669800 0000000100000004
raw: ffffea00026fc360 ffffea0002958b60 ffff88813fe74940 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8880a9669580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880a9669600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8880a9669680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff8880a9669700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880a9669780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================