audit: type=1400 audit(1517745179.393:14): avc:  denied  { write } for  pid=5635 comm="syz-executor1" scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=netlink_fib_lookup_socket permissive=1
==================================================================
BUG: KASAN: double-free or invalid-free in relay_open+0x603/0x860 kernel/relay.c:614

CPU: 1 PID: 5641 Comm: syz-executor6 Not tainted 4.9.80-gb30d2b5 #28
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801c556f8b8 ffffffff81d94b69 ffffea0006f12c80 ffff8801bc4b2780
 ffff8801da001280 ffffffff8137d8a3 0000000000000282 ffff8801c556f8f0
 ffffffff8153e093 ffff8801bc4b2780 ffffffff8137d8a3 ffff8801da001280
Call Trace:
 [<ffffffff81d94b69>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d94b69>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff8153e093>] print_address_description+0x73/0x280 mm/kasan/report.c:252
 [<ffffffff8153e304>] kasan_report_double_free+0x64/0xa0 mm/kasan/report.c:333
 [<ffffffff8153da34>] kasan_slab_free+0xa4/0xc0 mm/kasan/kasan.c:572
 [<ffffffff8153a583>] slab_free_hook mm/slub.c:1355 [inline]
 [<ffffffff8153a583>] slab_free_freelist_hook mm/slub.c:1377 [inline]
 [<ffffffff8153a583>] slab_free mm/slub.c:2958 [inline]
 [<ffffffff8153a583>] kfree+0x103/0x300 mm/slub.c:3878
 [<ffffffff8137d8a3>] relay_open+0x603/0x860 kernel/relay.c:614
 [<ffffffff813bf609>] do_blk_trace_setup+0x3e9/0x950 kernel/trace/blktrace.c:501
 [<ffffffff813bfc50>] blk_trace_setup+0xe0/0x1a0 kernel/trace/blktrace.c:545
 [<ffffffff813c013e>] blk_trace_ioctl+0x1de/0x300 kernel/trace/blktrace.c:654
 [<ffffffff81d38310>] blkdev_ioctl+0xb00/0x1a60 block/ioctl.c:576
 [<ffffffff8162c5fe>] block_ioctl+0xde/0x120 fs/block_dev.c:1688
 [<ffffffff815ae71a>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff815ae71a>] do_vfs_ioctl+0x1aa/0x1140 fs/ioctl.c:679
 [<ffffffff815af73f>] SYSC_ioctl fs/ioctl.c:694 [inline]
 [<ffffffff815af73f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 [<ffffffff838b346e>] entry_SYSCALL_64_fastpath+0x29/0xe8

Allocated by task 5641:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
 save_stack+0x43/0xd0 mm/kasan/kasan.c:505
 set_track mm/kasan/kasan.c:517 [inline]
 kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:609
 kmem_cache_alloc_trace+0xfb/0x2a0 mm/slub.c:2742
 kmalloc include/linux/slab.h:490 [inline]
 kzalloc include/linux/slab.h:636 [inline]
 relay_open+0x91/0x860 kernel/relay.c:576
 do_blk_trace_setup+0x3e9/0x950 kernel/trace/blktrace.c:501
 blk_trace_setup+0xe0/0x1a0 kernel/trace/blktrace.c:545
 blk_trace_ioctl+0x1de/0x300 kernel/trace/blktrace.c:654
 blkdev_ioctl+0xb00/0x1a60 block/ioctl.c:576
 block_ioctl+0xde/0x120 fs/block_dev.c:1688
 vfs_ioctl fs/ioctl.c:43 [inline]
 do_vfs_ioctl+0x1aa/0x1140 fs/ioctl.c:679
 SYSC_ioctl fs/ioctl.c:694 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 entry_SYSCALL_64_fastpath+0x29/0xe8

Freed by task 5641:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
 save_stack+0x43/0xd0 mm/kasan/kasan.c:505
 set_track mm/kasan/kasan.c:517 [inline]
 kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:582
 slab_free_hook mm/slub.c:1355 [inline]
 slab_free_freelist_hook mm/slub.c:1377 [inline]
 slab_free mm/slub.c:2958 [inline]
 kfree+0x103/0x300 mm/slub.c:3878
 relay_destroy_channel+0x16/0x20 kernel/relay.c:199
 kref_sub include/linux/kref.h:73 [inline]
 kref_put include/linux/kref.h:98 [inline]
 relay_open+0x5ea/0x860 kernel/relay.c:612
 do_blk_trace_setup+0x3e9/0x950 kernel/trace/blktrace.c:501
 blk_trace_setup+0xe0/0x1a0 kernel/trace/blktrace.c:545
 blk_trace_ioctl+0x1de/0x300 kernel/trace/blktrace.c:654
 blkdev_ioctl+0xb00/0x1a60 block/ioctl.c:576
 block_ioctl+0xde/0x120 fs/block_dev.c:1688
 vfs_ioctl fs/ioctl.c:43 [inline]
 do_vfs_ioctl+0x1aa/0x1140 fs/ioctl.c:679
 SYSC_ioctl fs/ioctl.c:694 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 entry_SYSCALL_64_fastpath+0x29/0xe8

The buggy address belongs to the object at ffff8801bc4b2780
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 512-byte region [ffff8801bc4b2780, ffff8801bc4b2980)
The buggy address belongs to the page:
page:ffffea0006f12c80 count:1 mapcount:0 mapping:          (null) index:0x0 compound_mapcount: 0
flags: 0x8000000000004080(slab|head)
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801bc4b2680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801bc4b2700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8801bc4b2780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff8801bc4b2800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801bc4b2880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================