[syzbot] BUG: unable to handle kernel NULL pointer dereference in htb_select_queue

[syzbot]

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 <max...@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+b53a70...@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 syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
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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

[Eric Dumazet]

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;
return dev->netdev_ops->ndo_setup_tc(dev, TC_SETUP_QDISC_HTB, opt);
}

[Maxim Mikityanskiy]

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.

[Eric Dumazet]

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.

You probably also need this :


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)

[Maxim Mikityanskiy]

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.

[Eric Dumazet]

Yes, but htb_destroy() will crash, as I tried to point out ;)

>
>> 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.

Sure.

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
BUG: unable to handle kernel NULL pointer dereference in htb_select_queue

BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor instruction fetch in kernel mode
#PF: error_code(0x0010) - not-present page

PGD 1829d067 P4D 1829d067 PUD 334b7067 PMD 0

Oops: 0010 [#1] PREEMPT SMP KASAN

CPU: 1 PID: 11142 Comm: syz-executor.3 Not tainted 5.12.0-rc2-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:ffffc900021774e8 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: 1ffff9200042ee9e RCX: 0000000000000000
RDX: ffffc90002177520 RSI: 0000000000000012 RDI: ffff888022e94000
RBP: ffff888022e94000 R08: 00000000fffffff1 R09: 0000000000000400
R10: ffffffff871a8554 R11: 0000000000000000 R12: ffffffff89eb1300
R13: dffffc0000000000 R14: ffff888016344000 R15: 00000000ffff0000
FS: 00007f55a9dbc700(0000) GS:ffff8880b9f00000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: ffffffffffffffd6 CR3: 0000000034ad4000 CR4: 00000000001506e0

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:654 [inline]
sock_sendmsg+0xcf/0x120 net/socket.c:674
____sys_sendmsg+0x6e8/0x810 net/socket.c:2350
___sys_sendmsg+0xf3/0x170 net/socket.c:2404
__sys_sendmsg+0xe5/0x1b0 net/socket.c:2433
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xae

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:00007f55a9dbc188 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: 00007ffeb05219af R14: 00007f55a9dbc300 R15: 0000000000022000

Modules linked in:
CR2: 0000000000000000

---[ end trace e88486434fe01eaa ]---

RIP: 0010:0x0
Code: Unable to access opcode bytes at RIP 0xffffffffffffffd6.

RSP: 0018:ffffc900021774e8 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: 1ffff9200042ee9e RCX: 0000000000000000
RDX: ffffc90002177520 RSI: 0000000000000012 RDI: ffff888022e94000
RBP: ffff888022e94000 R08: 00000000fffffff1 R09: 0000000000000400
R10: ffffffff871a8554 R11: 0000000000000000 R12: ffffffff89eb1300
R13: dffffc0000000000 R14: ffff888016344000 R15: 00000000ffff0000
FS: 00007f55a9dbc700(0000) GS:ffff8880b9f00000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: ffffffffffffffd6 CR3: 0000000034ad4000 CR4: 00000000001506e0

DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

Tested on:

commit: a74e6a01 Merge tag 's390-5.12-3' of git://git.kernel.org/p..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=147fa48ad00000
kernel config: https://syzkaller.appspot.com/x/.config?x=db54a40779209160
dashboard link: https://syzkaller.appspot.com/bug?extid=b53a709f04722ca12a3c
compiler: