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Date: Wed, 10 Mar 2021 16:54:24 +0200
From: Maxim Mikityanskiy <maximmi@...dia.com>
To: Eric Dumazet <eric.dumazet@...il.com>,
syzbot <syzbot+b53a709f04722ca12a3c@...kaller.appspotmail.com>,
<davem@...emloft.net>, <jhs@...atatu.com>, <jiri@...nulli.us>,
<kuba@...nel.org>, <linux-kernel@...r.kernel.org>,
<maximmi@...lanox.com>, <netdev@...r.kernel.org>,
<syzkaller-bugs@...glegroups.com>, <tariqt@...dia.com>,
<xiyou.wangcong@...il.com>
Subject: Re: [syzbot] BUG: unable to handle kernel NULL pointer dereference in
htb_select_queue
On 2021-03-09 17:20, Eric Dumazet wrote:
>
>
> On 3/9/21 4:13 PM, syzbot wrote:
>> Hello,
>>
>> syzbot found the following issue on:
>>
>> HEAD commit: 38b5133a octeontx2-pf: Fix otx2_get_fecparam()
>> git tree: net-next
>> console output: https://syzkaller.appspot.com/x/log.txt?x=166288a8d00000
>> kernel config: https://syzkaller.appspot.com/x/.config?x=dbc1ca9e55dc1f9f
>> dashboard link: https://syzkaller.appspot.com/bug?extid=b53a709f04722ca12a3c
>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=119454ccd00000
>>
>> The issue was bisected to:
>>
>> commit d03b195b5aa015f6c11988b86a3625f8d5dbac52
>> Author: Maxim Mikityanskiy <maximmi@...lanox.com>
>> Date: Tue Jan 19 12:08:13 2021 +0000
>>
>> sch_htb: Hierarchical QoS hardware offload
>>
>> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=13ab12ecd00000
>> final oops: https://syzkaller.appspot.com/x/report.txt?x=106b12ecd00000
>> console output: https://syzkaller.appspot.com/x/log.txt?x=17ab12ecd00000
>>
>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>> Reported-by: syzbot+b53a709f04722ca12a3c@...kaller.appspotmail.com
>> Fixes: d03b195b5aa0 ("sch_htb: Hierarchical QoS hardware offload")
>>
>> BUG: kernel NULL pointer dereference, address: 0000000000000000
>> #PF: supervisor instruction fetch in kernel mode
>> #PF: error_code(0x0010) - not-present page
>> PGD 183fe067 P4D 183fe067 PUD 21aef067 PMD 0
>> Oops: 0010 [#1] PREEMPT SMP KASAN
>> CPU: 0 PID: 10125 Comm: syz-executor.0 Not tainted 5.11.0-rc7-syzkaller #0
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
>> RIP: 0010:0x0
>> Code: Unable to access opcode bytes at RIP 0xffffffffffffffd6.
>> RSP: 0018:ffffc9000a9c74e8 EFLAGS: 00010246
>> RAX: dffffc0000000000 RBX: 1ffff92001538e9e RCX: 0000000000000000
>> RDX: ffffc9000a9c7520 RSI: 0000000000000012 RDI: ffff88802d158000
>> RBP: ffff88802d158000 R08: 00000000fffffff1 R09: 0000000000000400
>> R10: ffffffff871631c4 R11: 0000000000000000 R12: ffffffff89ea6b40
>> R13: dffffc0000000000 R14: ffff888012b79c00 R15: 00000000ffff0000
>> FS: 00007f73f9698700(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
>> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: ffffffffffffffd6 CR3: 00000000173b5000 CR4: 00000000001506f0
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> Call Trace:
>> htb_offload net/sched/sch_htb.c:1011 [inline]
>> htb_select_queue+0x17f/0x2c0 net/sched/sch_htb.c:1349
>> tc_modify_qdisc+0x44a/0x1a50 net/sched/sch_api.c:1657
>> rtnetlink_rcv_msg+0x44e/0xad0 net/core/rtnetlink.c:5553
>> netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2502
>> netlink_unicast_kernel net/netlink/af_netlink.c:1312 [inline]
>> netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1338
>> netlink_sendmsg+0x856/0xd90 net/netlink/af_netlink.c:1927
>> sock_sendmsg_nosec net/socket.c:652 [inline]
>> sock_sendmsg+0xcf/0x120 net/socket.c:672
>> ____sys_sendmsg+0x6e8/0x810 net/socket.c:2348
>> ___sys_sendmsg+0xf3/0x170 net/socket.c:2402
>> __sys_sendmsg+0xe5/0x1b0 net/socket.c:2435
>> do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>> entry_SYSCALL_64_after_hwframe+0x44/0xa9
>> RIP: 0033:0x466019
>> Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
>> RSP: 002b:00007f73f9698188 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
>> RAX: ffffffffffffffda RBX: 000000000056bf60 RCX: 0000000000466019
>> RDX: 0000000000000000 RSI: 00000000200007c0 RDI: 0000000000000004
>> RBP: 00000000004bd067 R08: 0000000000000000 R09: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000246 R12: 000000000056bf60
>> R13: 00007fffefccc11f R14: 00007f73f9698300 R15: 0000000000022000
>> Modules linked in:
>> CR2: 0000000000000000
>> ---[ end trace e1544e8206616773 ]---
>> RIP: 0010:0x0
>> Code: Unable to access opcode bytes at RIP 0xffffffffffffffd6.
>> RSP: 0018:ffffc9000a9c74e8 EFLAGS: 00010246
>> RAX: dffffc0000000000 RBX: 1ffff92001538e9e RCX: 0000000000000000
>> RDX: ffffc9000a9c7520 RSI: 0000000000000012 RDI: ffff88802d158000
>> RBP: ffff88802d158000 R08: 00000000fffffff1 R09: 0000000000000400
>> R10: ffffffff871631c4 R11: 0000000000000000 R12: ffffffff89ea6b40
>> R13: dffffc0000000000 R14: ffff888012b79c00 R15: 00000000ffff0000
>> FS: 00007f73f9698700(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
>> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: ffffffffffffffd6 CR3: 00000000173b5000 CR4: 00000000001506e0
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>>
>>
>> ---
>> This report 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.
>>
>> syzbot will keep track of this issue. 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 issue, for details see:
>> https://goo.gl/tpsmEJ#testing-patches
>>
>
>
> Hmm... what about this :
>
> diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
> index f87d07736a1404edcfd17a792321758cd4bdd173..680afb5bfe2294a5531c7aaeed698b95ea3ab20c 100644
> --- a/net/sched/sch_api.c
> +++ b/net/sched/sch_api.c
> @@ -1651,15 +1651,16 @@ static int tc_modify_qdisc(struct sk_buff *skb, struct nlmsghdr *n,
> err = -ENOENT;
> }
> } else {
> - struct netdev_queue *dev_queue;
> + struct netdev_queue *dev_queue = NULL;
>
> if (p && p->ops->cl_ops && p->ops->cl_ops->select_queue)
> dev_queue = p->ops->cl_ops->select_queue(p, tcm);
> - else if (p)
> - dev_queue = p->dev_queue;
> - else
> - dev_queue = netdev_get_tx_queue(dev, 0);
> -
> + if (!dev_queue) {
> + if (p)
> + dev_queue = p->dev_queue;
> + else
> + dev_queue = netdev_get_tx_queue(dev, 0);
> + }
> q = qdisc_create(dev, dev_queue, p,
> tcm->tcm_parent, tcm->tcm_handle,
> tca, &err, extack);
> diff --git a/net/sched/sch_htb.c b/net/sched/sch_htb.c
> index dff3adf5a9156c2412c64a10ad1b2ce9e1367433..cc6eccd688701ae00255f07e32fb4b0efbaf45ce 100644
> --- a/net/sched/sch_htb.c
> +++ b/net/sched/sch_htb.c
> @@ -1008,6 +1008,8 @@ static void htb_set_lockdep_class_child(struct Qdisc *q)
>
> static int htb_offload(struct net_device *dev, struct tc_htb_qopt_offload *opt)
> {
> + if (!tc_can_offload(dev) || !dev->netdev_ops->ndo_setup_tc)
> + return -EOPNOTSUPP;
My fault, all calls to htb_offload must be protected by if (q->offload).
Rather than checking tc_can_offload and ndo_setup_tc in htb_offload
every time, I suggest to fix htb_select_queue:
diff --git a/net/sched/sch_htb.c b/net/sched/sch_htb.c
index dff3adf5a915..b23203159996 100644
--- a/net/sched/sch_htb.c
+++ b/net/sched/sch_htb.c
@@ -1340,8 +1340,12 @@ htb_select_queue(struct Qdisc *sch, struct tcmsg
*tcm)
{
struct net_device *dev = qdisc_dev(sch);
struct tc_htb_qopt_offload offload_opt;
+ struct htb_sched *q = qdisc_priv(sch);
int err;
+ if (!q->offload)
+ return sch->dev_queue;
+
offload_opt = (struct tc_htb_qopt_offload) {
.command = TC_HTB_LEAF_QUERY_QUEUE,
.classid = TC_H_MIN(tcm->tcm_parent),
htb_init ensures that tc_can_offload and ndo_setup_tc are checked if
q->offload is true. Also, we can avoid changing tc_modify_qdisc if
htb_select_queue mimics its behavior in non-offload mode, as shown above.
There is also a case where htb_select_queue returns NULL on errors, and
that is handled in qdisc_create (the error message will be "No device
queue given"), which I think is a sane behavior.
What do you think of this fix? If it fits, I'll send it as a patch.
> return dev->netdev_ops->ndo_setup_tc(dev, TC_SETUP_QDISC_HTB, opt);
> }
>
>
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