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BUG: KASAN: use-after-free in vgem_gem_dumb_create+0x22c/0x240 drivers/gpu/drm/vgem/vgem_drv.c:214
Read of size 8 at addr ffff8880a2d21b00 by task syz-executor041/8440

CPU: 0 PID: 8440 Comm: syz-executor041 Not tainted 4.19.188-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1fc/0x2ef lib/dump_stack.c:118
 print_address_description.cold+0x54/0x219 mm/kasan/report.c:256
 kasan_report_error.cold+0x8a/0x1b9 mm/kasan/report.c:354
 kasan_report mm/kasan/report.c:412 [inline]
 __asan_report_load8_noabort+0x88/0x90 mm/kasan/report.c:433
 vgem_gem_dumb_create+0x22c/0x240 drivers/gpu/drm/vgem/vgem_drv.c:214
 drm_mode_create_dumb+0x27c/0x300 drivers/gpu/drm/drm_dumb_buffers.c:92
 drm_ioctl_kernel+0x208/0x2a0 drivers/gpu/drm/drm_ioctl.c:757
 drm_ioctl+0x507/0x9c0 drivers/gpu/drm/drm_ioctl.c:857
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:501 [inline]
 do_vfs_ioctl+0xcdb/0x12e0 fs/ioctl.c:688
 ksys_ioctl+0x9b/0xc0 fs/ioctl.c:705
 __do_sys_ioctl fs/ioctl.c:712 [inline]
 __se_sys_ioctl fs/ioctl.c:710 [inline]
 __x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:710
 do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x449fc9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 11 15 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f06b03c3308 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004ca448 RCX: 0000000000449fc9
RDX: 00000000200000c0 RSI: 00000000c02064b2 RDI: 0000000000000006
RBP: 00000000004ca440 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000004ca44c
R13: 000000000049a074 R14: 6972642f7665642f R15: 0000000000022000

Allocated by task 8440:
 kmem_cache_alloc_trace+0x12f/0x380 mm/slab.c:3625
 kmalloc include/linux/slab.h:515 [inline]
 kzalloc include/linux/slab.h:709 [inline]
 __vgem_gem_create+0x44/0xf0 drivers/gpu/drm/vgem/vgem_drv.c:158
 vgem_gem_create drivers/gpu/drm/vgem/vgem_drv.c:187 [inline]
 vgem_gem_dumb_create+0xcf/0x240 drivers/gpu/drm/vgem/vgem_drv.c:210
 drm_mode_create_dumb+0x27c/0x300 drivers/gpu/drm/drm_dumb_buffers.c:92
 drm_ioctl_kernel+0x208/0x2a0 drivers/gpu/drm/drm_ioctl.c:757
 drm_ioctl+0x507/0x9c0 drivers/gpu/drm/drm_ioctl.c:857
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:501 [inline]
 do_vfs_ioctl+0xcdb/0x12e0 fs/ioctl.c:688
 ksys_ioctl+0x9b/0xc0 fs/ioctl.c:705
 __do_sys_ioctl fs/ioctl.c:712 [inline]
 __se_sys_ioctl fs/ioctl.c:710 [inline]
 __x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:710
 do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 8440:
 __cache_free mm/slab.c:3503 [inline]
 kfree+0xcc/0x210 mm/slab.c:3822
 drm_gem_object_free+0x91/0x1c0 drivers/gpu/drm/drm_gem.c:837
 kref_put include/linux/kref.h:70 [inline]
 drm_gem_object_put_unlocked+0xd1/0x180 drivers/gpu/drm/drm_gem.c:866
 vgem_gem_create drivers/gpu/drm/vgem/vgem_drv.c:192 [inline]
 vgem_gem_dumb_create+0x10c/0x240 drivers/gpu/drm/vgem/vgem_drv.c:210
 drm_mode_create_dumb+0x27c/0x300 drivers/gpu/drm/drm_dumb_buffers.c:92
 drm_ioctl_kernel+0x208/0x2a0 drivers/gpu/drm/drm_ioctl.c:757
 drm_ioctl+0x507/0x9c0 drivers/gpu/drm/drm_ioctl.c:857
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:501 [inline]
 do_vfs_ioctl+0xcdb/0x12e0 fs/ioctl.c:688
 ksys_ioctl+0x9b/0xc0 fs/ioctl.c:705
 __do_sys_ioctl fs/ioctl.c:712 [inline]
 __se_sys_ioctl fs/ioctl.c:710 [inline]
 __x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:710
 do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8880a2d21a00
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 256 bytes inside of
 512-byte region [ffff8880a2d21a00, ffff8880a2d21c00)
The buggy address belongs to the page:
page:ffffea00028b4840 count:1 mapcount:0 mapping:ffff88813bff0940 index:0x0
flags: 0xfff00000000100(slab)
raw: 00fff00000000100 ffffea00025d8008 ffffea0002843648 ffff88813bff0940
raw: 0000000000000000 ffff8880a2d21000 0000000100000006 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8880a2d21a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880a2d21a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8880a2d21b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff8880a2d21b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880a2d21c00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
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