Re: WARNING: refcount bug in __sk_destruct

From: Eric Dumazet
Date: Sun Mar 01 2020 - 21:38:38 EST

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In reply to: Eric Dumazet: "Re: WARNING: refcount bug in __sk_destruct"
Next in thread: Eric Dumazet: "Re: WARNING: refcount bug in __sk_destruct"
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On 3/1/20 6:22 PM, Eric Dumazet wrote:
>
>
> On 3/1/20 5:33 PM, syzbot wrote:
>> Hello,
>>
>> syzbot found the following crash on:
>>
>> HEAD commit: fd786fb1 net: convert suitable drivers to use phy_do_ioctl..
>> git tree: net-next
>> console output: https://syzkaller.appspot.com/x/log.txt?x=14e9726ee00000
>> kernel config: https://syzkaller.appspot.com/x/.config?x=7f93900a7904130d
>> dashboard link: https://syzkaller.appspot.com/bug?extid=dd803bc0e8adf0003261
>> compiler: gcc (GCC) 9.0.0 20181231 (experimental)
>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12af9369e00000
>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10583d76e00000
>>
>> The bug was bisected to:
>>
>> commit 14215108a1fd7e002c0a1f9faf8fbaf41fdda50d
>> Author: Cong Wang <xiyou.wangcong@xxxxxxxxx>
>> Date: Thu Feb 21 05:37:42 2019 +0000
>>
>> net_sched: initialize net pointer inside tcf_exts_init()
>>
>> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=175b66bee00000
>> final crash: https://syzkaller.appspot.com/x/report.txt?x=14db66bee00000
>> console output: https://syzkaller.appspot.com/x/log.txt?x=10db66bee00000
>>
>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> Reported-by: syzbot+dd803bc0e8adf0003261@xxxxxxxxxxxxxxxxxxxxxxxxx
>> Fixes: 14215108a1fd ("net_sched: initialize net pointer inside tcf_exts_init()")
>>
>> RBP: 0000000000000000 R08: 0000000000000002 R09: 00000000bb1414ac
>> R10: 0000000000000000 R11: 0000000000000246 R12: ffffffffffffffff
>> R13: 0000000000000009 R14: 0000000000000000 R15: 0000000000000000
>> ------------[ cut here ]------------
>> refcount_t: underflow; use-after-free.
>> WARNING: CPU: 1 PID: 9577 at lib/refcount.c:28 refcount_warn_saturate+0x1dc/0x1f0 lib/refcount.c:28
>> Kernel panic - not syncing: panic_on_warn set ...
>> CPU: 1 PID: 9577 Comm: syz-executor327 Not tainted 5.5.0-rc6-syzkaller #0
>> 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+0x197/0x210 lib/dump_stack.c:118
>> panic+0x2e3/0x75c kernel/panic.c:221
>> __warn.cold+0x2f/0x3e kernel/panic.c:582
>> report_bug+0x289/0x300 lib/bug.c:195
>> fixup_bug arch/x86/kernel/traps.c:174 [inline]
>> fixup_bug arch/x86/kernel/traps.c:169 [inline]
>> do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:267
>> do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:286
>> invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1027
>> RIP: 0010:refcount_warn_saturate+0x1dc/0x1f0 lib/refcount.c:28
>> Code: e9 d8 fe ff ff 48 89 df e8 c1 f8 16 fe e9 85 fe ff ff e8 a7 77 d8 fd 48 c7 c7 e0 44 71 88 c6 05 9e 86 db 06 01 e8 93 27 a9 fd <0f> 0b e9 ac fe ff ff 0f 1f 00 66 2e 0f 1f 84 00 00 00 00 00 55 48
>> RSP: 0018:ffffc9000c067b00 EFLAGS: 00010282
>> RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
>> RDX: 0000000000000000 RSI: ffffffff815e5dd6 RDI: fffff5200180cf52
>> RBP: ffffc9000c067b10 R08: ffff8880a8630340 R09: ffffed1015d26621
>> R10: ffffed1015d26620 R11: ffff8880ae933107 R12: 0000000000000003
>> R13: ffff888090256000 R14: ffff8880a7e5c040 R15: ffff8880a7e5c044
>> refcount_sub_and_test include/linux/refcount.h:261 [inline]
>> refcount_dec_and_test include/linux/refcount.h:281 [inline]
>> put_net include/net/net_namespace.h:259 [inline]
>> __sk_destruct+0x6d8/0x7f0 net/core/sock.c:1723
>> sk_destruct+0xd5/0x110 net/core/sock.c:1739
>> __sk_free+0xfb/0x3f0 net/core/sock.c:1750
>> sk_free+0x83/0xb0 net/core/sock.c:1761
>> sock_put include/net/sock.h:1719 [inline]
>> __tun_detach+0xbe0/0x1150 drivers/net/tun.c:728
>> tun_detach drivers/net/tun.c:740 [inline]
>> tun_chr_close+0xe0/0x180 drivers/net/tun.c:3455
>> __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
>> exit_task_work include/linux/task_work.h:22 [inline]
>> do_exit+0xba9/0x2f50 kernel/exit.c:801
>> do_group_exit+0x135/0x360 kernel/exit.c:899
>> __do_sys_exit_group kernel/exit.c:910 [inline]
>> __se_sys_exit_group kernel/exit.c:908 [inline]
>> __x64_sys_exit_group+0x44/0x50 kernel/exit.c:908
>> do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
>> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>> RIP: 0033:0x441a48
>> Code: Bad RIP value.
>> RSP: 002b:00007fffe55809a8 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
>> RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 0000000000441a48
>> RDX: 0000000000000001 RSI: 000000000000003c RDI: 0000000000000001
>> RBP: 00000000004c8430 R08: 00000000000000e7 R09: ffffffffffffffd0
>> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
>> R13: 00000000006dba80 R14: 0000000000000000 R15: 0000000000000000
>> Kernel Offset: disabled
>> Rebooting in 86400 seconds..
>>
>>
>> ---
>> 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#status for how to communicate with syzbot.
>> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
>> syzbot can test patches for this bug, for details see:
>> https://goo.gl/tpsmEJ#testing-patches
>>
>
>
> Hmmm... maybe this patch would fix it ?
>
> diff --git a/include/net/pkt_cls.h b/include/net/pkt_cls.h
> index a972244ab1931a2fd52a41efa4f7a6cd78d8746a..6e258a6c1328e38a757d9711f4116a6672995b8f 100644
> --- a/include/net/pkt_cls.h
> +++ b/include/net/pkt_cls.h
> @@ -206,11 +206,12 @@ static inline int tcf_exts_init(struct tcf_exts *exts, struct net *net,
> #ifdef CONFIG_NET_CLS_ACT
> exts->type = 0;
> exts->nr_actions = 0;
> - exts->net = net;
> + exts->net = NULL;
> exts->actions = kcalloc(TCA_ACT_MAX_PRIO, sizeof(struct tc_action *),
> GFP_KERNEL);
> if (!exts->actions)
> return -ENOMEM;
> + exts->net = net;
> #endif
> exts->action = action;
> exts->police = police;
>

Hmm no.

Instead, make sure cls_u32 gets a reference so that calls
to u32_destroy_key(new, false); do not end up decrementing netns refcount.

diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index e15ff335953deef36e55901d8f4ce34e15ed676f..587d71def49157680cf54f84558c4f4e5dad37f1 100644
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -898,6 +898,7 @@ static int u32_change(struct net *net, struct sk_buff *in_skb,
new = u32_init_knode(net, tp, n);
if (!new)
return -ENOMEM;
+ tcf_exts_get_net(&new->exts);

err = u32_set_parms(net, tp, base, new, tb,
tca[TCA_RATE], ovr, extack);
@@ -918,7 +919,6 @@ static int u32_change(struct net *net, struct sk_buff *in_skb,

u32_replace_knode(tp, tp_c, new);
tcf_unbind_filter(tp, &n->res);
- tcf_exts_get_net(&n->exts);
tcf_queue_work(&n->rwork, u32_delete_key_work);
return 0;
}

Next message: Pingfan Liu: "Re: [PATCHv5 3/3] mm/gup_benchemark: add LONGTERM_BENCHMARK test in gup fast path"
Previous message: Ye Bin: "[PATCH] vt: fix CVE-2020-8647"
In reply to: Eric Dumazet: "Re: WARNING: refcount bug in __sk_destruct"
Next in thread: Eric Dumazet: "Re: WARNING: refcount bug in __sk_destruct"
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