netdev - Re: [PATCH net-next] net_sched: fix a regression in tcf_proto_lookup

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Date:	Fri, 20 Dec 2013 12:11:20 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Cong Wang <xiyou.wangcong@...il.com>
Cc:	Jamal Hadi Salim <jhs@...atatu.com>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH net-next] net_sched: fix a regression in
 tcf_proto_lookup_ops()

On Fri, 2013-12-20 at 11:57 -0800, Cong Wang wrote:

> Then why mirred_cleanup_module() appears in the top of your backtrace?

Because you have not understood the trace ?

Thats exactly why its not useful at all.


[   76.656061] RIP: 0010:[<ffffffffa008d882>]  [<ffffffffa008d882>] mirred_cleanup_module+0x13a/0x2a [act_mirred]^M


This means RIP is _after_ mirred_cleanup_module() body, as this function size if 0x2a bytes

We were trying to execute a data portion which happens to be in
the neighboring of innocent mirred_cleanup_module()

When not using module, trace was different and made no sense anyway :

[   86.909685] kernel tried to execute NX-protected page - exploit attempt? (uid: 0)^M
[   86.917183] BUG: unable to handle kernel paging request at ffffffff818a4b80^M
[   86.924190] IP: [<ffffffff818a4b80>] 0xffffffff818a4b80^M
[   86.929439] PGD 180c067 PUD 180d063 PMD 202e851063 PTE 80000000018a4163^M
[   86.936144] Oops: 0011 [#1] SMP ^M
[   86.939405] Modules linked in: cls_tcindex sch_dsmark xt_multiport iptable_mangle w1_therm wire cdc_acm uhci_hcd ehci_hcd i2c_dev i2c_i801 i2c_core msr cpuid ib_uverbs mlx4_ib ib_sa ib_mad mlx4_en ib_core mlx4_core ipv6^M
[   86.959307] CPU: 11 PID: 11378 Comm: BweTCTree_DoWor Not tainted 3.13.0-smp-DEV #413^M
[   86.973964] task: ffff880078fc6690 ti: ffff882016886000 task.ti: ffff882016886000^M
[   86.981467] RIP: 0010:[<ffffffff818a4b80>]  [<ffffffff818a4b80>] 0xffffffff818a4b80^M
[   86.989153] RSP: 0018:ffff8820168879b0  EFLAGS: 00010206^M
[   86.994482] RAX: 0000000000010000 RBX: ffff881015c59480 RCX: 0000000000000000^M
[   87.001635] RDX: ffffffff818a4b50 RSI: ffffffffa0059790 RDI: ffff881015c59480^M
[   87.008772] RBP: ffff882016887aa8 R08: ffff88107f4004c0 R09: ffff881015c59480^M
[   87.015922] R10: ffff880000077680 R11: 00000000ffffff97 R12: ffff881016ae9160^M
[   87.023094] R13: ffff881016ae9000 R14: ffff881016ae9000 R15: ffff88102e405800^M
[   87.030277] FS:  00007f29f3858700(0000) GS:ffff88107fb60000(0000) knlGS:0000000000000000^M
[   87.038386] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033^M
[   87.044146] CR2: ffffffff818a4b80 CR3: 0000002030af1000 CR4: 00000000001407e0^M
[   87.051301] Stack:^M
[   87.053314]  ffffffff814dd0e1 0000000000000028 00000000ffffffff ffffffff818a4b50^M
[   87.060774]  ffff880000077680 ffff88102e405824 0000000800000000 ffffffff818a1940^M
[   87.068232]  0000000000000000 ffffffff8169ca80 0001000000010000 ffff882016887a68^M
[   87.075750] Call Trace:^M
[   87.078202]  [<ffffffff814dd0e1>] ? tc_ctl_tfilter+0x4a1/0x760^M
[   87.084071]  [<ffffffff814e6fb6>] ? __netlink_sendskb+0x56/0x130^M
[   87.090108]  [<ffffffff814caa04>] rtnetlink_rcv_msg+0xa4/0x240^M
[   87.095945]  [<ffffffff814ca960>] ? __rtnl_unlock+0x20/0x20^M
[   87.101538]  [<ffffffff814e9e91>] netlink_rcv_skb+0xb1/0xc0^M
[   87.107118]  [<ffffffff814c7635>] rtnetlink_rcv+0x25/0x40^M
[   87.112528]  [<ffffffff814e973d>] netlink_unicast+0x14d/0x1f0^M
[   87.118314]  [<ffffffff814e9ae3>] netlink_sendmsg+0x303/0x410^M
[   87.124092]  [<ffffffff814a048c>] sock_sendmsg+0x9c/0xd0^M
[   87.129451]  [<ffffffff814a0da0>] ? move_addr_to_kernel+0x40/0xa0^M
[   87.135566]  [<ffffffff814add21>] ? verify_iovec+0x51/0xd0^M
[   87.141064]  [<ffffffff814a0c21>] ___sys_sendmsg+0x3c1/0x3d0^M
[   87.146747]  [<ffffffff815690bc>] ? __do_page_fault+0x26c/0x500^M
[   87.152689]  [<ffffffff811821ab>] ? do_brk+0x1bb/0x320^M
[   87.157830]  [<ffffffff814a1809>] __sys_sendmsg+0x49/0x90^M
[   87.163250]  [<ffffffff814a1862>] SyS_sendmsg+0x12/0x20^M
[   87.168484]  [<ffffffff8156d992>] system_call_fastpath+0x16/0x1b^M
[   87.174518] Code: ff ff ff 80 97 05 a0 ff ff ff ff 00 00 10 00 00 00 00 00 00 00 00 00 00 00 00 00 80 4b 8a 81 ff ff ff ff 80 4b 8a 81 ff ff ff ff <70> 4b 8a 81 ff ff ff ff 70 4b 8a 81 ff ff ff ff c0 9d ba 81 ff ^M
[   87.194642] RIP  [<ffffffff818a4b80>] 0xffffffff818a4b80^M
[   87.199983]  RSP <ffff8820168879b0>^M
[   87.203472] CR2: ffffffff818a4b80^M
[   87.206785] ---[ end trace 8ef37a4cc4cb5a8c ]---^M
[   87.211408] Kernel panic - not syncing: Fatal exception^M
[   87.216763] Rebooting in 10 seconds..^M

We actually try to execute code at ffffffff818a4b80 == &act_mirred_ops

ffffffff818a4b40 d cls_mod_lock
ffffffff818a4b50 d tcf_proto_base
ffffffff818a4b60 d act_mod_lock
ffffffff818a4b70 d act_base
ffffffff818a4b80 d act_mirred_ops
ffffffff818a4bf0 d mirred_device_notifier
ffffffff818a4c10 d mirred_list
ffffffff818a4c20 d _rs.42828
ffffffff818a4c40 d ematch_mod_lock
ffffffff818a4c50 d ematch_ops

So only a bisection actually gave me the faulty commit.

Stacktrace was absolutely useless.


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