netdev - Re: [PATCH bpf-next v11 2/4] bpf: added new helper bpf_get_ns_current_pid

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Message-ID: <12db0313-668e-3825-d5fa-28d0f675808c@fb.com>
Date:   Fri, 27 Sep 2019 16:59:37 +0000
From:   Yonghong Song <yhs@...com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Carlos Neira <cneirabustos@...il.com>
CC:     Networking <netdev@...r.kernel.org>,
        "ebiederm@...ssion.com" <ebiederm@...ssion.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next v11 2/4] bpf: added new helper
 bpf_get_ns_current_pid_tgid



On 9/27/19 9:15 AM, Andrii Nakryiko wrote:
> On Thu, Sep 26, 2019 at 1:15 AM Carlos Neira <cneirabustos@...il.com> wrote:
>>
>> New bpf helper bpf_get_ns_current_pid_tgid,
>> This helper will return pid and tgid from current task
>> which namespace matches dev_t and inode number provided,
>> this will allows us to instrument a process inside a container.
>>
>> Signed-off-by: Carlos Neira <cneirabustos@...il.com>
>> ---
>>   include/linux/bpf.h      |  1 +
>>   include/uapi/linux/bpf.h | 18 +++++++++++++++++-
>>   kernel/bpf/core.c        |  1 +
>>   kernel/bpf/helpers.c     | 32 ++++++++++++++++++++++++++++++++
>>   kernel/trace/bpf_trace.c |  2 ++
>>   5 files changed, 53 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
>> index 5b9d22338606..231001475504 100644
>> --- a/include/linux/bpf.h
>> +++ b/include/linux/bpf.h
>> @@ -1055,6 +1055,7 @@ extern const struct bpf_func_proto bpf_get_local_storage_proto;
>>   extern const struct bpf_func_proto bpf_strtol_proto;
>>   extern const struct bpf_func_proto bpf_strtoul_proto;
>>   extern const struct bpf_func_proto bpf_tcp_sock_proto;
>> +extern const struct bpf_func_proto bpf_get_ns_current_pid_tgid_proto;
>>
>>   /* Shared helpers among cBPF and eBPF. */
>>   void bpf_user_rnd_init_once(void);
>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
>> index 77c6be96d676..9272dc8fb08c 100644
>> --- a/include/uapi/linux/bpf.h
>> +++ b/include/uapi/linux/bpf.h
>> @@ -2750,6 +2750,21 @@ union bpf_attr {
>>    *             **-EOPNOTSUPP** kernel configuration does not enable SYN cookies
>>    *
>>    *             **-EPROTONOSUPPORT** IP packet version is not 4 or 6
>> + *
>> + * int bpf_get_ns_current_pid_tgid(u32 dev, u64 inum)
>> + *     Return
>> + *             A 64-bit integer containing the current tgid and pid from current task
> 
> Function signature doesn't correspond to the actual return type (int vs u64).
> 
>> + *              which namespace inode and dev_t matches , and is create as such:
>> + *             *current_task*\ **->tgid << 32 \|**
>> + *             *current_task*\ **->pid**.
>> + *
>> + *             On failure, the returned value is one of the following:
>> + *
>> + *             **-EINVAL** if dev and inum supplied don't match dev_t and inode number
>> + *              with nsfs of current task.
>> + *
>> + *             **-ENOENT** if /proc/self/ns does not exists.
>> + *
>>    */
> 
> [...]
> 
>>   #include "../../lib/kstrtox.h"
>>
>> @@ -487,3 +489,33 @@ const struct bpf_func_proto bpf_strtoul_proto = {
>>          .arg4_type      = ARG_PTR_TO_LONG,
>>   };
>>   #endif
>> +
>> +BPF_CALL_2(bpf_get_ns_current_pid_tgid, u32, dev, u64, inum)
> 
> Just curious, is dev_t officially specified as u32 and is never
> supposed to grow bigger? I wonder if accepting u64 might be more
> future-proof API here?

This is what we have now in kernel (include/linux/types.h)
typedef u32 __kernel_dev_t;
typedef __kernel_dev_t          dev_t;

But userspace dev_t (defined at /usr/include/sys/types.h) have
8 bytes.

Agree. Let us just use u64. It won't hurt and also will be fine
if kernel internal dev_t becomes 64bit.

> 
>> +{
>> +       struct task_struct *task = current;
>> +       struct pid_namespace *pidns;
> 
> [...]
>