==================================================================
BUG: KASAN: double-free or invalid-free in relay_open+0x6a1/0xa40 kernel/relay.c:614

CPU: 3 PID: 2976 Comm: syzkaller407767 Not tainted 4.14.0-rc5-next-20171018+ #8
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:16 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:52
 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:3492 [inline]
 kfree+0xca/0x250 mm/slab.c:3807
 relay_open+0x6a1/0xa40 kernel/relay.c:614
 do_blk_trace_setup+0x4a4/0xcf0 kernel/trace/blktrace.c:517
 blk_trace_setup+0xbd/0x180 kernel/trace/blktrace.c:564
 sg_ioctl+0xc71/0x2d90 drivers/scsi/sg.c:1089
 vfs_ioctl fs/ioctl.c:45 [inline]
 do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:685
 SYSC_ioctl fs/ioctl.c:700 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
 entry_SYSCALL_64_fastpath+0x1f/0xbe
RIP: 0033:0x439149
RSP: 002b:00007ffea4ba2668 EFLAGS: 00000206 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000439149
RDX: 000000002084cf90 RSI: 00000000c0481273 RDI: 0000000000000003
RBP: 0000000000000082 R08: 00000000000000fe R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
R13: 0000000000401da0 R14: 0000000000401e30 R15: 0000000000000000

Allocated by task 2976:
 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:3614
 kmalloc include/linux/slab.h:502 [inline]
 kzalloc include/linux/slab.h:691 [inline]
 relay_open+0xf2/0xa40 kernel/relay.c:576
 do_blk_trace_setup+0x4a4/0xcf0 kernel/trace/blktrace.c:517
 blk_trace_setup+0xbd/0x180 kernel/trace/blktrace.c:564
 sg_ioctl+0xc71/0x2d90 drivers/scsi/sg.c:1089
 vfs_ioctl fs/ioctl.c:45 [inline]
 do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:685
 SYSC_ioctl fs/ioctl.c:700 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
 entry_SYSCALL_64_fastpath+0x1f/0xbe

Freed by task 2976:
 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:3492 [inline]
 kfree+0xca/0x250 mm/slab.c:3807
 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+0x4a4/0xcf0 kernel/trace/blktrace.c:517
 blk_trace_setup+0xbd/0x180 kernel/trace/blktrace.c:564
 sg_ioctl+0xc71/0x2d90 drivers/scsi/sg.c:1089
 vfs_ioctl fs/ioctl.c:45 [inline]
 do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:685
 SYSC_ioctl fs/ioctl.c:700 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
 entry_SYSCALL_64_fastpath+0x1f/0xbe

The buggy address belongs to the object at ffff8800692f80c0
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 0 bytes inside of
 512-byte region [ffff8800692f80c0, ffff8800692f82c0)
The buggy address belongs to the page:
page:ffffea0001a4be00 count:1 mapcount:0 mapping:ffff8800692f80c0 index:0xffff8800692f8340
flags: 0x500000000000100(slab)
raw: 0500000000000100 ffff8800692f80c0 ffff8800692f8340 0000000100000004
raw: ffffea0001a436a0 ffffea0001a28d60 ffff88003e800940 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8800692f7f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8800692f8000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8800692f8080: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
                                           ^
 ffff8800692f8100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8800692f8180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================