Messages in this thread | | | Subject | Re: [syzbot] BUG: unable to handle kernel NULL pointer dereference in htb_select_queue | From | Maxim Mikityanskiy <> | Date | Wed, 10 Mar 2021 20:55:36 +0200 |
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On 2021-03-10 19:03, Eric Dumazet wrote: > > > On 3/10/21 3:54 PM, Maxim Mikityanskiy wrote: >> 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@mellanox.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@syzkaller.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@googlegroups.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. > > > I think that it is not enough, since you overwrite q->offload in htb_init() > even if an error will be provided. > > So a malicious user will find its way.
I doubt that, because if htb_init returns an error, the qdisc gets destroyed immediately (well, after a call to htb_destroy), and I believe all these operations are protected by RTNL, so a malicious user has no way to insert a call to another callback.
> You probably also need this :
However, I'll likely need something like this anyway, because HTB must not call ndo_setup_tc on destroy if it didn't call it on init. It may crash in a similar way if ndo_setup_tc is not implemented. Thanks for helping me spot that - if you don't mind, I'll base my second patch on your code below.
> > > diff --git a/net/sched/sch_htb.c b/net/sched/sch_htb.c > index dff3adf5a9156c2412c64a10ad1b2ce9e1367433..d15ee7cf33b34221d09dfc81105dcb6c2b2fd489 100644 > --- a/net/sched/sch_htb.c > +++ b/net/sched/sch_htb.c > @@ -1020,6 +1020,7 @@ static int htb_init(struct Qdisc *sch, struct nlattr *opt, > struct nlattr *tb[TCA_HTB_MAX + 1]; > struct tc_htb_glob *gopt; > unsigned int ntx; > + bool offload; > int err; > > qdisc_watchdog_init(&q->watchdog, sch); > @@ -1044,9 +1045,9 @@ static int htb_init(struct Qdisc *sch, struct nlattr *opt, > if (gopt->version != HTB_VER >> 16) > return -EINVAL; > > - q->offload = nla_get_flag(tb[TCA_HTB_OFFLOAD]); > + offload = nla_get_flag(tb[TCA_HTB_OFFLOAD]); > > - if (q->offload) { > + if (offload) { > if (sch->parent != TC_H_ROOT) > return -EOPNOTSUPP; > > @@ -1060,6 +1061,7 @@ static int htb_init(struct Qdisc *sch, struct nlattr *opt, > if (!q->direct_qdiscs) > return -ENOMEM; > } > + q->offload = offload; > > err = qdisc_class_hash_init(&q->clhash); > if (err < 0) >
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