Re: KASAN: use-after-free Read in handle_userfault (2)

From: Dmitry Vyukov
Date: Sun Dec 30 2018 - 02:48:39 EST

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On Wed, Dec 12, 2018 at 10:58 AM Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
>
> On Wed, Dec 12, 2018 at 10:45 AM syzbot
> <syzbot+cbc64b24b2b2d54c07a9@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> >
> > Hello,
> >
> > syzbot found the following crash on:
> >
> > HEAD commit: 14cf8c1d5b90 Add linux-next specific files for 20181210
> > git tree: linux-next
> > console output: https://syzkaller.appspot.com/x/log.txt?x=133296db400000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=c9133d0a4284c012
> > dashboard link: https://syzkaller.appspot.com/bug?extid=cbc64b24b2b2d54c07a9
> > compiler: gcc (GCC) 8.0.1 20180413 (experimental)
>
> This is a corrupted/intermixed kernel output, the bug actually
> happened somewhere in net/core/neighbour.c.
> syzkaller has a bunch of code to try to deal to corrupted kernel
> output, but it's not always possible as a parallel thread printing
> something can inject an unrelated frame just in the right place, and
> then it's indistinguishable from a crash happened there.
>
> The question is: what's the significance of that
> "FAULT_FLAG_ALLOW_RETRY missing 70"?
> Is it something to fix in kernel? Can the check be removed? Should it
> be moved somewhere earlier when flags are passed to kernel and cause
> EINVAL? Can it be at least converted to a single-line pr_warn?
> +Sasha go as far as suggesting that any "Call Trace:" in kernel output
> means a kernel bugs. This is one of few places in kernel that dumps
> stacks left and right without a kernel bug (?).

up

anybody maintaining uffd?

> > 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+cbc64b24b2b2d54c07a9@xxxxxxxxxxxxxxxxxxxxxxxxx
> >
> > RDX: 00000000000003ff RSI: 0000000020012fe0 RDI: 00007f5dbe489850
> > RBP: 000000000072bf00 R08: 00000000000003ff R09: 0000000000000000
> > R10: 0000000000000000 R11: 0000000000000246 R12: 00007f5dbe48a6d4
> > R13: 00000000004c578a R14: 00000000004d9d90 R15: 00000000ffffffff
> > ==================================================================
> > BUG: KASAN: use-after-free in __list_del_entry_valid+0xf1/0x100
> > lib/list_debug.c:51
> > CPU: 1 PID: 20306 Comm: syz-executor2 Not tainted 4.20.0-rc6-next-20181210+
> > #164
> > Read of size 8 at addr ffff8881c5e72bb0 by task kworker/0:1/12
> > 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+0x244/0x39d lib/dump_stack.c:113
> > handle_userfault.cold.30+0x47/0x62 fs/userfaultfd.c:431
> > do_anonymous_page mm/memory.c:2938 [inline]
> > handle_pte_fault mm/memory.c:3780 [inline]
> > __handle_mm_fault+0x4d26/0x5b70 mm/memory.c:3906
> > handle_mm_fault+0x54f/0xc70 mm/memory.c:3943
> > do_user_addr_fault arch/x86/mm/fault.c:1475 [inline]
> > __do_page_fault+0x5f6/0xd70 arch/x86/mm/fault.c:1541
> > do_page_fault+0xf2/0x7e0 arch/x86/mm/fault.c:1572
> > page_fault+0x1e/0x30 arch/x86/entry/entry_64.S:1143
> > RIP: 0033:0x4510a0
> > Code: 0f 84 c4 0f 00 00 48 89 f1 48 89 f8 48 83 e1 3f 48 83 f9 20 0f 86 7b
> > 02 00 00 48 83 e6 f0 48 83 e1 0f 66 0f ef c0 66 0f ef c9 <66> 0f 74 0e 66
> > 0f d7 d1 48 d3 ea 49 c7 c2 11 00 00 00 49 29 ca 4d
> > RSP: 002b:00007fab1fbba7a8 EFLAGS: 00010202
> > RAX: 00007fab1fbba850 RBX: 0000000000000003 RCX: 000000000000000e
> > RDX: 00000000000003ff RSI: 0000000020012fe0 RDI: 00007fab1fbba850
> > RBP: 000000000072bf00 R08: 00000000000003ff R09: 0000000000000000
> > R10: 0000000000000000 R11: 0000000000000246 R12: 00007fab1fbbb6d4
> > R13: 00000000004c578a R14: 00000000004d9d90 R15: 00000000ffffffff
> > CPU: 0 PID: 12 Comm: kworker/0:1 Not tainted 4.20.0-rc6-next-20181210+ #164
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> > Google 01/01/2011
> > Workqueue: events_power_efficient neigh_periodic_work
> > Call Trace:
> > __dump_stack lib/dump_stack.c:77 [inline]
> > dump_stack+0x244/0x39d lib/dump_stack.c:113
> > print_address_description.cold.4+0x9/0x1ff mm/kasan/report.c:187
> > kasan_report.cold.5+0x1b/0x39 mm/kasan/report.c:317
> > __asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:135
> > __list_del_entry_valid+0xf1/0x100 lib/list_debug.c:51
> > __list_del_entry include/linux/list.h:117 [inline]
> > list_del_init include/linux/list.h:159 [inline]
> > neigh_mark_dead+0x13b/0x410 net/core/neighbour.c:125
> > neigh_periodic_work+0x89a/0xc30 net/core/neighbour.c:905
> > process_one_work+0xc90/0x1c40 kernel/workqueue.c:2153
> > worker_thread+0x17f/0x1390 kernel/workqueue.c:2296
> > kthread+0x35a/0x440 kernel/kthread.c:246
> > ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352
> >
> > Allocated by task 8166:
> > save_stack+0x43/0xd0 mm/kasan/common.c:73
> > set_track mm/kasan/common.c:85 [inline]
> > kasan_kmalloc+0xcb/0xd0 mm/kasan/common.c:482
> > __do_kmalloc_node mm/slab.c:3671 [inline]
> > __kmalloc_node_track_caller+0x4d/0x70 mm/slab.c:3685
> > __kmalloc_reserve.isra.38+0x41/0xe0 net/core/skbuff.c:137
> > __alloc_skb+0x155/0x770 net/core/skbuff.c:205
> > alloc_skb include/linux/skbuff.h:1008 [inline]
> > netlink_alloc_large_skb net/netlink/af_netlink.c:1182 [inline]
> > netlink_sendmsg+0xb29/0xfc0 net/netlink/af_netlink.c:1892
> > sock_sendmsg_nosec net/socket.c:622 [inline]
> > sock_sendmsg+0xd5/0x120 net/socket.c:632
> > ___sys_sendmsg+0x7fd/0x930 net/socket.c:2117
> > __sys_sendmsg+0x11d/0x280 net/socket.c:2155
> > __do_sys_sendmsg net/socket.c:2164 [inline]
> > __se_sys_sendmsg net/socket.c:2162 [inline]
> > __x64_sys_sendmsg+0x78/0xb0 net/socket.c:2162
> > do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
> > entry_SYSCALL_64_after_hwframe+0x49/0xbe
> >
> > Freed by task 8166:
> > save_stack+0x43/0xd0 mm/kasan/common.c:73
> > set_track mm/kasan/common.c:85 [inline]
> > __kasan_slab_free+0x102/0x150 mm/kasan/common.c:444
> > kasan_slab_free+0xe/0x10 mm/kasan/common.c:452
> > __cache_free mm/slab.c:3485 [inline]
> > kfree+0xcf/0x230 mm/slab.c:3804
> > skb_free_head+0x99/0xc0 net/core/skbuff.c:550
> > skb_release_data+0x70c/0x9a0 net/core/skbuff.c:570
> > skb_release_all+0x4a/0x60 net/core/skbuff.c:627
> > __kfree_skb net/core/skbuff.c:641 [inline]
> > consume_skb+0x1ae/0x570 net/core/skbuff.c:701
> > netlink_unicast_kernel net/netlink/af_netlink.c:1311 [inline]
> > netlink_unicast+0x5ad/0x760 net/netlink/af_netlink.c:1336
> > netlink_sendmsg+0xa18/0xfc0 net/netlink/af_netlink.c:1917
> > sock_sendmsg_nosec net/socket.c:622 [inline]
> > sock_sendmsg+0xd5/0x120 net/socket.c:632
> > ___sys_sendmsg+0x7fd/0x930 net/socket.c:2117
> > __sys_sendmsg+0x11d/0x280 net/socket.c:2155
> > __do_sys_sendmsg net/socket.c:2164 [inline]
> > __se_sys_sendmsg net/socket.c:2162 [inline]
> > __x64_sys_sendmsg+0x78/0xb0 net/socket.c:2162
> > do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
> > entry_SYSCALL_64_after_hwframe+0x49/0xbe
> >
> > The buggy address belongs to the object at ffff8881c5e72940
> > which belongs to the cache kmalloc-1k of size 1024
> > The buggy address is located 624 bytes inside of
> > 1024-byte region [ffff8881c5e72940, ffff8881c5e72d40)
> > The buggy address belongs to the page:
> > page:ffffea0007179c80 count:1 mapcount:0 mapping:ffff8881da800ac0
> > index:0xffff8881c5e72dc0 compound_mapcount: 0
> > flags: 0x2fffc0000010200(slab|head)
> > raw: 02fffc0000010200 ffffea00072cf188 ffffea00075d0c08 ffff8881da800ac0
> > raw: ffff8881c5e72dc0 ffff8881c5e72040 0000000100000005 0000000000000000
> > page dumped because: kasan: bad access detected
> >
> > Memory state around the buggy address:
> > ffff8881c5e72a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > ffff8881c5e72b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > > ffff8881c5e72b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > ^
> > ffff8881c5e72c00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > ffff8881c5e72c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > ==================================================================
> > kobject: 'loop5' (00000000a3f9d928): kobject_uevent_env
> >
> >
> > ---
> > 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@xxxxxxxxxxxxxxxxx
> >
> > syzbot will keep track of this bug report. See:
> > https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with
> > syzbot.
> >
> > --
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