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BUG: KASAN: slab-out-of-bounds in css_task_iter_advance+0x49b/0x540 kernel/cgroup/cgroup.c:4507
Read of size 4 at addr ffff88808c12d01c by task syz-executor.1/20217

CPU: 0 PID: 20217 Comm: syz-executor.1 Not tainted 5.2.0-rc3-next-20190607 #11
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+0x172/0x1f0 lib/dump_stack.c:113
 print_address_description.cold+0xd4/0x306 mm/kasan/report.c:351
 __kasan_report.cold+0x1b/0x36 mm/kasan/report.c:482
 kasan_report+0x12/0x20 mm/kasan/common.c:614
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/generic_report.c:131
 css_task_iter_advance+0x49b/0x540 kernel/cgroup/cgroup.c:4507
 css_task_iter_start+0x18b/0x230 kernel/cgroup/cgroup.c:4543
 pidlist_array_load+0x181/0xa80 kernel/cgroup/cgroup-v1.c:372
 cgroup_pidlist_start+0x37e/0x4c0 kernel/cgroup/cgroup-v1.c:442
 cgroup_seqfile_start+0xa4/0xd0 kernel/cgroup/cgroup.c:3752
 kernfs_seq_start+0xdc/0x190 fs/kernfs/file.c:118
 seq_read+0x2a7/0x1110 fs/seq_file.c:224
 kernfs_fop_read+0xed/0x560 fs/kernfs/file.c:252
 do_loop_readv_writev fs/read_write.c:714 [inline]
 do_loop_readv_writev fs/read_write.c:701 [inline]
 do_iter_read+0x4a4/0x660 fs/read_write.c:935
 vfs_readv+0xf0/0x160 fs/read_write.c:997
 kernel_readv fs/splice.c:359 [inline]
 default_file_splice_read+0x475/0x890 fs/splice.c:414
 do_splice_to+0x127/0x180 fs/splice.c:877
 splice_direct_to_actor+0x2d2/0x970 fs/splice.c:954
 do_splice_direct+0x1da/0x2a0 fs/splice.c:1063
 do_sendfile+0x597/0xd00 fs/read_write.c:1464
 __do_sys_sendfile64 fs/read_write.c:1525 [inline]
 __se_sys_sendfile64 fs/read_write.c:1511 [inline]
 __x64_sys_sendfile64+0x1dd/0x220 fs/read_write.c:1511
 do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x459279
Code: fd b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 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 0f 83 cb b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fb057255c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 0000000000459279
RDX: 0000000000000000 RSI: 0000000000000005 RDI: 0000000000000006
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 000000000000fffc R11: 0000000000000246 R12: 00007fb0572566d4
R13: 00000000004c6835 R14: 00000000004db7a8 R15: 00000000ffffffff

Allocated by task 19563:
 save_stack+0x23/0x90 mm/kasan/common.c:71
 set_track mm/kasan/common.c:79 [inline]
 __kasan_kmalloc mm/kasan/common.c:489 [inline]
 __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:462
 kasan_kmalloc+0x9/0x10 mm/kasan/common.c:503
 __do_kmalloc_node mm/slab.c:3614 [inline]
 __kmalloc_node_track_caller+0x4e/0x70 mm/slab.c:3628
 __kmalloc_reserve.isra.0+0x40/0xf0 net/core/skbuff.c:139
 __alloc_skb+0x10b/0x5e0 net/core/skbuff.c:207
 alloc_skb include/linux/skbuff.h:1054 [inline]
 __ip6_append_data.isra.0+0x2a24/0x3640 net/ipv6/ip6_output.c:1514
 ip6_append_data+0x1e5/0x320 net/ipv6/ip6_output.c:1683
 rawv6_sendmsg+0x1347/0x35d0 net/ipv6/raw.c:947
 inet_sendmsg+0x141/0x5d0 net/ipv4/af_inet.c:798
 sock_sendmsg_nosec net/socket.c:646 [inline]
 sock_sendmsg+0xd7/0x130 net/socket.c:665
 ___sys_sendmsg+0x3e2/0x920 net/socket.c:2287
 __sys_sendmmsg+0x1bf/0x4d0 net/socket.c:2389
 __do_sys_sendmmsg net/socket.c:2418 [inline]
 __se_sys_sendmmsg net/socket.c:2415 [inline]
 __x64_sys_sendmmsg+0x9d/0x100 net/socket.c:2415
 do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 19563:
 save_stack+0x23/0x90 mm/kasan/common.c:71
 set_track mm/kasan/common.c:79 [inline]
 __kasan_slab_free+0x102/0x150 mm/kasan/common.c:451
 kasan_slab_free+0xe/0x10 mm/kasan/common.c:459
 __cache_free mm/slab.c:3426 [inline]
 kfree+0x106/0x2a0 mm/slab.c:3753
 skb_free_head+0x93/0xb0 net/core/skbuff.c:589
 skb_release_data+0x42d/0x7c0 net/core/skbuff.c:609
 skb_release_all+0x4d/0x60 net/core/skbuff.c:663
 __kfree_skb net/core/skbuff.c:677 [inline]
 kfree_skb net/core/skbuff.c:695 [inline]
 kfree_skb+0xe8/0x390 net/core/skbuff.c:689
 __skb_queue_purge include/linux/skbuff.h:2719 [inline]
 inet_sock_destruct+0x10b/0x830 net/ipv4/af_inet.c:134
 __sk_destruct+0x53/0x6e0 net/core/sock.c:1694
 sk_destruct+0x7b/0x90 net/core/sock.c:1733
 __sk_free+0xce/0x300 net/core/sock.c:1744
 sk_free+0x42/0x50 net/core/sock.c:1755
 sock_put include/net/sock.h:1723 [inline]
 sk_common_release+0x21c/0x330 net/core/sock.c:3175
 rawv6_close+0x68/0x90 net/ipv6/raw.c:1245
 inet_release+0xe0/0x1f0 net/ipv4/af_inet.c:427
 inet6_release+0x53/0x80 net/ipv6/af_inet6.c:470
 __sock_release+0xce/0x2a0 net/socket.c:601
 sock_close+0x1b/0x30 net/socket.c:1273
 __fput+0x2ff/0x890 fs/file_table.c:280
 ____fput+0x16/0x20 fs/file_table.c:313
 task_work_run+0x145/0x1c0 kernel/task_work.c:113
 get_signal+0x2007/0x2490 kernel/signal.c:2522
 do_signal+0x87/0x1990 arch/x86/kernel/signal.c:815
 exit_to_usermode_loop+0x244/0x2c0 arch/x86/entry/common.c:164
 prepare_exit_to_usermode arch/x86/entry/common.c:199 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:279 [inline]
 do_syscall_64+0x58e/0x680 arch/x86/entry/common.c:304
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff88808c12d080
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 100 bytes to the left of
 512-byte region [ffff88808c12d080, ffff88808c12d280)
The buggy address belongs to the page:
page:ffffea0002304b40 refcount:1 mapcount:0 mapping:ffff8880aa400940 index:0x0
flags: 0x1fffc0000000200(slab)
raw: 01fffc0000000200 ffffea000293c088 ffffea000235c408 ffff8880aa400940
raw: 0000000000000000 ffff88808c12d080 0000000100000006 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88808c12cf00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff88808c12cf80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88808c12d000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                            ^
 ffff88808c12d080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88808c12d100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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