audit: type=1400 audit(1516040265.869:11): avc:  denied  { sys_chroot } for  pid=4786 comm="syz-executor6" capability=18  scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=cap_userns permissive=1
==================================================================
BUG: KASAN: double-free or invalid-free in relay_open+0x6a1/0xa40 kernel/relay.c:614

CPU: 1 PID: 4805 Comm: syz-executor6 Not tainted 4.15.0-rc8+ #263
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+0x194/0x257 lib/dump_stack.c:53
 print_address_description+0x73/0x250 mm/kasan/report.c:252
 kasan_report_double_free+0x55/0x80 mm/kasan/report.c:333
 kasan_slab_free+0xa3/0xc0 mm/kasan/kasan.c:514
 __cache_free mm/slab.c:3488 [inline]
 kfree+0xd6/0x260 mm/slab.c:3803
 relay_open+0x6a1/0xa40 kernel/relay.c:614
 do_blk_trace_setup+0x4a4/0xcd0 kernel/trace/blktrace.c:544
 __blk_trace_setup+0xbe/0x150 kernel/trace/blktrace.c:589
 blk_trace_ioctl+0x206/0x2e0 kernel/trace/blktrace.c:728
 blkdev_ioctl+0x1845/0x1e00 block/ioctl.c:587
 block_ioctl+0xde/0x120 fs/block_dev.c:1860
 vfs_ioctl fs/ioctl.c:46 [inline]
 do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
 entry_SYSCALL_64_fastpath+0x29/0xa0
RIP: 0033:0x452cf9
RSP: 002b:00007fe59a4f7c58 EFLAGS: 00000212 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 000000000071bea0 RCX: 0000000000452cf9
RDX: 0000000020beaf68 RSI: 00000000c0481273 RDI: 0000000000000013
RBP: 0000000000000406 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f4130
R13: 00000000ffffffff R14: 00007fe59a4f86d4 R15: 0000000000000000

Allocated by task 4805:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:551
 kmem_cache_alloc_trace+0x136/0x750 mm/slab.c:3610
 kmalloc include/linux/slab.h:499 [inline]
 kzalloc include/linux/slab.h:688 [inline]
 relay_open+0xf2/0xa40 kernel/relay.c:576
 do_blk_trace_setup+0x4a4/0xcd0 kernel/trace/blktrace.c:544
 __blk_trace_setup+0xbe/0x150 kernel/trace/blktrace.c:589
 blk_trace_ioctl+0x206/0x2e0 kernel/trace/blktrace.c:728
 blkdev_ioctl+0x1845/0x1e00 block/ioctl.c:587
 block_ioctl+0xde/0x120 fs/block_dev.c:1860
 vfs_ioctl fs/ioctl.c:46 [inline]
 do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
 entry_SYSCALL_64_fastpath+0x29/0xa0

Freed by task 4805:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524
 __cache_free mm/slab.c:3488 [inline]
 kfree+0xd6/0x260 mm/slab.c:3803
 relay_destroy_channel kernel/relay.c:199 [inline]
 kref_put include/linux/kref.h:70 [inline]
 relay_open+0x84a/0xa40 kernel/relay.c:612
 do_blk_trace_setup+0x4a4/0xcd0 kernel/trace/blktrace.c:544
 __blk_trace_setup+0xbe/0x150 kernel/trace/blktrace.c:589
 blk_trace_ioctl+0x206/0x2e0 kernel/trace/blktrace.c:728
 blkdev_ioctl+0x1845/0x1e00 block/ioctl.c:587
 block_ioctl+0xde/0x120 fs/block_dev.c:1860
 vfs_ioctl fs/ioctl.c:46 [inline]
 do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
 entry_SYSCALL_64_fastpath+0x29/0xa0

The buggy address belongs to the object at ffff8801bc18e540
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 512-byte region [ffff8801bc18e540, ffff8801bc18e740)
The buggy address belongs to the page:
page:ffffea0006f06380 count:1 mapcount:0 mapping:ffff8801bc18e040 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801bc18e040 0000000000000000 0000000100000006
raw: ffffea00070bf120 ffff8801dac01748 ffff8801dac00940 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801bc18e400: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8801bc18e480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8801bc18e500: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
                                           ^
 ffff8801bc18e580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801bc18e600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================