Date:   Sun, 1 Sep 2019 20:31:47 -0700
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     syzbot <syzbot+0025447b4cb6f208558f@...kaller.appspotmail.com>
Cc:     David Miller <davem@...emloft.net>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: KASAN: use-after-free Write in __xfrm_policy_unlink (2)

On Thu, May 16, 2019 at 3:35 AM syzbot
<syzbot+0025447b4cb6f208558f@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    3b0f31f2 genetlink: make policy common to family
> git tree:       net-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=12a319df200000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=f05902bca21d8935
> dashboard link: https://syzkaller.appspot.com/bug?extid=0025447b4cb6f208558f
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
>
> Unfortunately, I don't have any reproducer for this crash yet.
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+0025447b4cb6f208558f@...kaller.appspotmail.com

This looks like what has been fixed by:

#syz fix:
xfrm: policy: Fix out-of-bound array accesses in __xfrm_policy_unlink


> ==================================================================
> BUG: KASAN: use-after-free in __write_once_size
> include/linux/compiler.h:220 [inline]
> BUG: KASAN: use-after-free in __hlist_del include/linux/list.h:713 [inline]
> BUG: KASAN: use-after-free in hlist_del_rcu include/linux/rculist.h:455
> [inline]
> BUG: KASAN: use-after-free in __xfrm_policy_unlink+0x4b1/0x5c0
> net/xfrm/xfrm_policy.c:2212
> Write of size 8 at addr ffff8880a55a9e80 by task kworker/u4:6/7431
>
> CPU: 1 PID: 7431 Comm: kworker/u4:6 Not tainted 5.0.0+ #106
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Workqueue: netns cleanup_net
> Call Trace:
>   __dump_stack lib/dump_stack.c:77 [inline]
>   dump_stack+0x172/0x1f0 lib/dump_stack.c:113
>   print_address_description.cold+0x7c/0x20d mm/kasan/report.c:187
>   kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317
>   __asan_report_store8_noabort+0x17/0x20 mm/kasan/generic_report.c:137
>   __write_once_size include/linux/compiler.h:220 [inline]
>   __hlist_del include/linux/list.h:713 [inline]
>   hlist_del_rcu include/linux/rculist.h:455 [inline]
>   __xfrm_policy_unlink+0x4b1/0x5c0 net/xfrm/xfrm_policy.c:2212
>   xfrm_policy_flush+0x331/0x460 net/xfrm/xfrm_policy.c:1789
>   xfrm_policy_fini+0x49/0x3a0 net/xfrm/xfrm_policy.c:3871
>   xfrm_net_exit+0x1d/0x70 net/xfrm/xfrm_policy.c:3933
>   ops_exit_list.isra.0+0xb0/0x160 net/core/net_namespace.c:153
>   cleanup_net+0x3fb/0x960 net/core/net_namespace.c:551
>   process_one_work+0x98e/0x1790 kernel/workqueue.c:2269
>   worker_thread+0x98/0xe40 kernel/workqueue.c:2415
>   kthread+0x357/0x430 kernel/kthread.c:253
>   ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352
>
> Allocated by task 7242:
>   save_stack+0x45/0xd0 mm/kasan/common.c:75
>   set_track mm/kasan/common.c:87 [inline]
>   __kasan_kmalloc mm/kasan/common.c:497 [inline]
>   __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:470
>   kasan_kmalloc+0x9/0x10 mm/kasan/common.c:511
>   __do_kmalloc mm/slab.c:3726 [inline]
>   __kmalloc+0x15c/0x740 mm/slab.c:3735
>   kmalloc include/linux/slab.h:550 [inline]
>   kzalloc include/linux/slab.h:740 [inline]
>   ext4_htree_store_dirent+0x8a/0x650 fs/ext4/dir.c:450
>   htree_dirblock_to_tree+0x4fe/0x910 fs/ext4/namei.c:1021
>   ext4_htree_fill_tree+0x252/0xa50 fs/ext4/namei.c:1098
>   ext4_dx_readdir fs/ext4/dir.c:574 [inline]
>   ext4_readdir+0x1999/0x3490 fs/ext4/dir.c:121
>   iterate_dir+0x489/0x5f0 fs/readdir.c:51
>   __do_sys_getdents fs/readdir.c:231 [inline]
>   __se_sys_getdents fs/readdir.c:212 [inline]
>   __x64_sys_getdents+0x1dd/0x370 fs/readdir.c:212
>   do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> Freed by task 7242:
>   save_stack+0x45/0xd0 mm/kasan/common.c:75
>   set_track mm/kasan/common.c:87 [inline]
>   __kasan_slab_free+0x102/0x150 mm/kasan/common.c:459
>   kasan_slab_free+0xe/0x10 mm/kasan/common.c:467
>   __cache_free mm/slab.c:3498 [inline]
>   kfree+0xcf/0x230 mm/slab.c:3821
>   free_rb_tree_fname+0x87/0xe0 fs/ext4/dir.c:402
>   ext4_htree_free_dir_info fs/ext4/dir.c:424 [inline]
>   ext4_release_dir+0x46/0x70 fs/ext4/dir.c:622
>   __fput+0x2e5/0x8d0 fs/file_table.c:278
>   ____fput+0x16/0x20 fs/file_table.c:309
>   task_work_run+0x14a/0x1c0 kernel/task_work.c:113
>   tracehook_notify_resume include/linux/tracehook.h:188 [inline]
>   exit_to_usermode_loop+0x273/0x2c0 arch/x86/entry/common.c:166
>   prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
>   syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
>   do_syscall_64+0x52d/0x610 arch/x86/entry/common.c:293
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> The buggy address belongs to the object at ffff8880a55a9e80
>   which belongs to the cache kmalloc-64 of size 64
> The buggy address is located 0 bytes inside of
>   64-byte region [ffff8880a55a9e80, ffff8880a55a9ec0)
> The buggy address belongs to the page:
> page:ffffea0002956a40 count:1 mapcount:0 mapping:ffff88812c3f0340 index:0x0
> flags: 0x1fffc0000000200(slab)
> raw: 01fffc0000000200 ffffea0002a0d748 ffffea00018af1c8 ffff88812c3f0340
> raw: 0000000000000000 ffff8880a55a9000 0000000100000020 0000000000000000
> page dumped because: kasan: bad access detected
>
> Memory state around the buggy address:
>   ffff8880a55a9d80: 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc
>   ffff8880a55a9e00: 00 00 00 00 04 fc fc fc fc fc fc fc fc fc fc fc
> > ffff8880a55a9e80: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>                     ^
>   ffff8880a55a9f00: 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc fc
>   ffff8880a55a9f80: 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc fc
> ==================================================================
>
>
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
>
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>
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