Re: [PATCH bpf-next V9 1/3] bpf: new helper to obtain namespace data from current task

[Yonghong Song <yhs@fb.com>]

On 8/28/19 1:39 PM, Carlos Antonio Neira Bustos wrote:
> Yonghong,
> 
> Thanks for the pointer, I fixed this bug, but I found another one that's triggered
> now the test program I included in  tools/testing/selftests/bpf/test_pidns.
> It's seemed that fname was not correctly setup when passing it to filename_lookup.
> This is fixed now and I'm doing some more testing.
> I think I'll remove the tests on samples/bpf as they are mostly end on -EPERM as
> the fix intended.
> Is ok to remove them and just focus to finish the self tests code?.

Yes, the samples/bpf test case can be removed.
Could you create a selftest with tracpoint net/netif_receive_skb, which 
also uses the proposed helper? net/netif_receive_skb will happen in
interrupt context and it should catch the issue as well if 
filename_lookup still get called in interrupt context.

> 
> Bests
> 
> On Wed, Aug 14, 2019 at 01:25:06AM -0400, carlos antonio neira bustos wrote:
>> Thank you very much!
>>
>> Bests
>>
>> El mié., 14 de ago. de 2019 00:50, Yonghong Song <yhs@fb.com> escribió:
>>
>>>
>>>
>>> On 8/13/19 5:56 PM, Carlos Antonio Neira Bustos wrote:
>>>> On Tue, Aug 13, 2019 at 11:11:14PM +0000, Yonghong Song wrote:
>>>>>
>>>>>
>>>>> On 8/13/19 11:47 AM, Carlos Neira wrote:
>>>>>> From: Carlos <cneirabustos@gmail.com>
>>>>>>
>>>>>> New bpf helper bpf_get_current_pidns_info.
>>>>>> This helper obtains the active namespace from current and returns
>>>>>> pid, tgid, device and namespace id as seen from that namespace,
>>>>>> allowing to instrument a process inside a container.
>>>>>>
>>>>>> Signed-off-by: Carlos Neira <cneirabustos@gmail.com>
>>>>>> ---
>>>>>>     fs/internal.h            |  2 --
>>>>>>     fs/namei.c               |  1 -
>>>>>>     include/linux/bpf.h      |  1 +
>>>>>>     include/linux/namei.h    |  4 +++
>>>>>>     include/uapi/linux/bpf.h | 31 ++++++++++++++++++++++-
>>>>>>     kernel/bpf/core.c        |  1 +
>>>>>>     kernel/bpf/helpers.c     | 64
>>> ++++++++++++++++++++++++++++++++++++++++++++++++
>>>>>>     kernel/trace/bpf_trace.c |  2 ++
>>>>>>     8 files changed, 102 insertions(+), 4 deletions(-)
>>>>>>
>>> [...]
>>>>>>
>>>>>> +BPF_CALL_2(bpf_get_current_pidns_info, struct bpf_pidns_info *,
>>> pidns_info, u32,
>>>>>> +    size)
>>>>>> +{
>>>>>> +   const char *pidns_path = "/proc/self/ns/pid";
>>>>>> +   struct pid_namespace *pidns = NULL;
>>>>>> +   struct filename *tmp = NULL;
>>>>>> +   struct inode *inode;
>>>>>> +   struct path kp;
>>>>>> +   pid_t tgid = 0;
>>>>>> +   pid_t pid = 0;
>>>>>> +   int ret;
>>>>>> +   int len;
>>>>>
>>>>
>>>> Thank you very much for catching this!.
>>>> Could you share how to replicate this bug?.
>>>
>>> The config is attached. just run trace_ns_info and you
>>> can reproduce the issue.
>>>
>>>>
>>>>> I am running your sample program and get the following kernel bug:
>>>>>
>>>>> ...
>>>>> [   26.414825] BUG: sleeping function called from invalid context at
>>>>> /data/users/yhs/work/net-next/fs
>>>>> /dcache.c:843
>>>>> [   26.416314] in_atomic(): 1, irqs_disabled(): 0, pid: 1911, name: ping
>>>>> [   26.417189] CPU: 0 PID: 1911 Comm: ping Tainted: G        W
>>>>> 5.3.0-rc1+ #280
>>>>> [   26.418182] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
>>>>> BIOS 1.9.3-1.el7.centos 04/01/2
>>>>> 014
>>>>> [   26.419393] Call Trace:
>>>>> [   26.419697]  <IRQ>
>>>>> [   26.419960]  dump_stack+0x46/0x5b
>>>>> [   26.420434]  ___might_sleep+0xe4/0x110
>>>>> [   26.420894]  dput+0x2a/0x200
>>>>> [   26.421265]  walk_component+0x10c/0x280
>>>>> [   26.421773]  link_path_walk+0x327/0x560
>>>>> [   26.422280]  ? proc_ns_dir_readdir+0x1a0/0x1a0
>>>>> [   26.422848]  ? path_init+0x232/0x330
>>>>> [   26.423364]  path_lookupat+0x88/0x200
>>>>> [   26.423808]  ? selinux_parse_skb.constprop.69+0x124/0x430
>>>>> [   26.424521]  filename_lookup+0xaf/0x190
>>>>> [   26.425031]  ? simple_attr_release+0x20/0x20
>>>>> [   26.425560]  bpf_get_current_pidns_info+0xfa/0x190
>>>>> [   26.426168]  bpf_prog_83627154cefed596+0xe66/0x1000
>>>>> [   26.426779]  trace_call_bpf+0xb5/0x160
>>>>> [   26.427317]  ? __netif_receive_skb_core+0x1/0xbb0
>>>>> [   26.427929]  ? __netif_receive_skb_core+0x1/0xbb0
>>>>> [   26.428496]  kprobe_perf_func+0x4d/0x280
>>>>> [   26.428986]  ? tracing_record_taskinfo_skip+0x1a/0x30
>>>>> [   26.429584]  ? tracing_record_taskinfo+0xe/0x80
>>>>> [   26.430152]  ? ttwu_do_wakeup.isra.114+0xcf/0xf0
>>>>> [   26.430737]  ? __netif_receive_skb_core+0x1/0xbb0
>>>>> [   26.431334]  ? __netif_receive_skb_core+0x5/0xbb0
>>>>> [   26.431930]  kprobe_ftrace_handler+0x90/0xf0
>>>>> [   26.432495]  ftrace_ops_assist_func+0x63/0x100
>>>>> [   26.433060]  0xffffffffc03180bf
>>>>> [   26.433471]  ? __netif_receive_skb_core+0x1/0xbb0
>>>>> ...
>>>>>
>>>>> To prevent we are running in arbitrary task (e.g., idle task)
>>>>> context which may introduce sleeping issues, the following
>>>>> probably appropriate:
>>>>>
>>>>>           if (in_nmi() || in_softirq())
>>>>>                   return -EPERM;
>>>>>
>>>>> Anyway, if in nmi or softirq, the namespace and pid/tgid
>>>>> we get may be just accidentally associated with the bpf running
>>>>> context, but it could be in a different context. So such info
>>>>> is not reliable any way.
>>>>>
>>>>>> +
>>>>>> +   if (unlikely(size != sizeof(struct bpf_pidns_info)))
>>>>>> +           return -EINVAL;
>>>>>> +   pidns = task_active_pid_ns(current);
>>> [...]
>>>