==================================================================
BUG: KASAN: use-after-free in p9_poll_mux net/9p/trans_fd.c:622 [inline]
BUG: KASAN: use-after-free in p9_poll_workfn+0x2cc/0x330 net/9p/trans_fd.c:1097
Read of size 4 at addr ffff8801c3fa62a8 by task kworker/1:3/1837

CPU: 1 PID: 1837 Comm: kworker/1:3 Not tainted 4.9.122-g54068d6 #26
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events p9_poll_workfn
 ffff8801ce2bfb60 ffffffff81eb8829 ffffea00070fe980 ffff8801c3fa62a8
 0000000000000000 ffff8801c3fa62a8 ffff8801db321280 ffff8801ce2bfb98
 ffffffff8156b6be ffff8801c3fa62a8 0000000000000004 0000000000000000
Call Trace:
 [<ffffffff81eb8829>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb8829>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff8156b6be>] print_address_description+0x6c/0x234 mm/kasan/report.c:256
 [<ffffffff8156bac8>] kasan_report_error mm/kasan/report.c:355 [inline]
 [<ffffffff8156bac8>] kasan_report.cold.6+0x242/0x2fe mm/kasan/report.c:412
 [<ffffffff8153f2e4>] __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:432
 [<ffffffff839ca24c>] p9_poll_mux net/9p/trans_fd.c:622 [inline]
 [<ffffffff839ca24c>] p9_poll_workfn+0x2cc/0x330 net/9p/trans_fd.c:1097
 [<ffffffff8118f421>] process_one_work+0x7e1/0x1500 kernel/workqueue.c:2092
 [<ffffffff81190216>] worker_thread+0xd6/0x10a0 kernel/workqueue.c:2226
 [<ffffffff8119f38d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff83a00e9c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373

Allocated by task 15274:
 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+0xc7/0xe0 mm/kasan/kasan.c:609
 kmem_cache_alloc_trace+0xfd/0x2b0 mm/slub.c:2742
 kmalloc include/linux/slab.h:490 [inline]
 kzalloc include/linux/slab.h:636 [inline]
 p9_fd_open net/9p/trans_fd.c:792 [inline]
 p9_fd_create+0xf3/0x330 net/9p/trans_fd.c:1029
 p9_client_create+0x6ff/0x10a0 net/9p/client.c:1036
 v9fs_session_init+0x333/0x13a0 fs/9p/v9fs.c:343
 v9fs_mount+0x7d/0x810 fs/9p/vfs_super.c:130
 mount_fs+0x28c/0x370 fs/super.c:1206
 vfs_kern_mount.part.29+0xd1/0x3d0 fs/namespace.c:1000
 vfs_kern_mount fs/namespace.c:982 [inline]
 do_new_mount fs/namespace.c:2537 [inline]
 do_mount+0x3c9/0x2740 fs/namespace.c:2859
 SYSC_mount fs/namespace.c:3075 [inline]
 SyS_mount+0xfe/0x110 fs/namespace.c:3052
 do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 entry_SYSCALL_64_after_swapgs+0x5d/0xdb

Freed by task 15274:
 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+0xfb/0x310 mm/slub.c:3878
 p9_fd_close+0x298/0x330 net/9p/trans_fd.c:890
 p9_client_destroy+0x73/0x570 net/9p/client.c:1070
 v9fs_session_close+0x46/0x110 fs/9p/v9fs.c:434
 v9fs_kill_super+0x4e/0xa0 fs/9p/vfs_super.c:226
 deactivate_locked_super+0x75/0xd0 fs/super.c:310
 v9fs_mount+0x3c6/0x810 fs/9p/vfs_super.c:207
 mount_fs+0x28c/0x370 fs/super.c:1206
 vfs_kern_mount.part.29+0xd1/0x3d0 fs/namespace.c:1000
 vfs_kern_mount fs/namespace.c:982 [inline]
 do_new_mount fs/namespace.c:2537 [inline]
 do_mount+0x3c9/0x2740 fs/namespace.c:2859
 SYSC_mount fs/namespace.c:3075 [inline]
 SyS_mount+0xfe/0x110 fs/namespace.c:3052
 do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 entry_SYSCALL_64_after_swapgs+0x5d/0xdb

The buggy address belongs to the object at ffff8801c3fa6280
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 40 bytes inside of
 512-byte region [ffff8801c3fa6280, ffff8801c3fa6480)
The buggy address belongs to the page:
page:ffffea00070fe980 count:1 mapcount:0 mapping:          (null) index:0xffff8801c3fa6500 compound_mapcount: 0
flags: 0x8000000000004080(slab|head)
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801c3fa6180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801c3fa6200: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8801c3fa6280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                  ^
 ffff8801c3fa6300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801c3fa6380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================