Re: [PATCH bpf-next v10 2/4] bpf: new helper to obtain namespace data from current task New bpf helper bpf_get_current_pidns_info.

[Yonghong Song <yhs@fb.com>]

On 9/6/19 4:09 PM, Carlos Neira wrote:
> This helper(bpf_get_current_pidns_info) 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>
> ---
>   include/linux/bpf.h      |  1 +
>   include/uapi/linux/bpf.h | 35 +++++++++++++++++++-
>   kernel/bpf/core.c        |  1 +
>   kernel/bpf/helpers.c     | 86 ++++++++++++++++++++++++++++++++++++++++++++++++
>   kernel/trace/bpf_trace.c |  2 ++
>   5 files changed, 124 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 5b9d22338606..819cb1c84be0 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_current_pidns_info_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 b5889257cc33..3ec9aa1438b7 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -2747,6 +2747,32 @@ union bpf_attr {
>    *		**-EOPNOTSUPP** kernel configuration does not enable SYN cookies
>    *
>    *		**-EPROTONOSUPPORT** IP packet version is not 4 or 6
> + *
> + * int bpf_get_current_pidns_info(struct bpf_pidns_info *pidns, u32 size_of_pidns)
> + *	Description
> + *		Get tgid, pid and namespace id as seen by the current namespace,
> + *		and device major/minor numbers from /proc/self/ns/pid. Such
> + *		information is stored in *pidns* of size *size*.
> + *
> + *		This helper is used when pid filtering is needed inside a
> + *		container as bpf_get_current_tgid() helper always returns the
> + *		pid id as seen by the root namespace.
> + *	Return
> + *		0 on success
> + *
> + *		On failure, the returned value is one of the following:
> + *
> + *		**-EINVAL** if *size_of_pidns* is not valid or unable to get ns, pid
> + *		or tgid of the current task.
> + *
> + *		**-ENOENT** if /proc/self/ns/pid does not exists.
> + *
> + *		**-ENOENT** if /proc/self/ns does not exists.
> + *
> + *		**-ENOMEM** if helper internal allocation fails.

-ENOMEM can be removed.

> + *
> + *		**-EPERM** if not able to call helper.
> + *
>    */
>   #define __BPF_FUNC_MAPPER(FN)		\
>   	FN(unspec),			\
> @@ -2859,7 +2885,8 @@ union bpf_attr {
>   	FN(sk_storage_get),		\
>   	FN(sk_storage_delete),		\
>   	FN(send_signal),		\
> -	FN(tcp_gen_syncookie),
> +	FN(tcp_gen_syncookie),		\
> +	FN(get_current_pidns_info),
>   
>   /* integer value in 'imm' field of BPF_CALL instruction selects which helper
>    * function eBPF program intends to call
> @@ -3610,4 +3637,10 @@ struct bpf_sockopt {
>   	__s32	retval;
>   };
>   
> +struct bpf_pidns_info {
> +	__u32 dev;	/* dev_t from /proc/self/ns/pid inode */

    /* dev_t of pid namespace pseudo file (typically /proc/seelf/ns/pid) 
after following symbolic link */

> +	__u32 nsid;
> +	__u32 tgid;
> +	__u32 pid;
> +};
>   #endif /* _UAPI__LINUX_BPF_H__ */
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 8191a7db2777..3159f2a0188c 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -2038,6 +2038,7 @@ const struct bpf_func_proto bpf_get_current_uid_gid_proto __weak;
>   const struct bpf_func_proto bpf_get_current_comm_proto __weak;
>   const struct bpf_func_proto bpf_get_current_cgroup_id_proto __weak;
>   const struct bpf_func_proto bpf_get_local_storage_proto __weak;
> +const struct bpf_func_proto bpf_get_current_pidns_info __weak;
>   
>   const struct bpf_func_proto * __weak bpf_get_trace_printk_proto(void)
>   {
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 5e28718928ca..8dbe6347893c 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -11,6 +11,11 @@
>   #include <linux/uidgid.h>
>   #include <linux/filter.h>
>   #include <linux/ctype.h>
> +#include <linux/pid_namespace.h>
> +#include <linux/kdev_t.h>
> +#include <linux/stat.h>
> +#include <linux/namei.h>
> +#include <linux/version.h>
>   
>   #include "../../lib/kstrtox.h"
>   
> @@ -312,6 +317,87 @@ void copy_map_value_locked(struct bpf_map *map, void *dst, void *src,
>   	preempt_enable();
>   }
>   
> +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 *fname = NULL;
> +	struct inode *inode;
> +	struct path kp;
> +	pid_t tgid = 0;
> +	pid_t pid = 0;
> +	int ret = -EINVAL;
> +	int len;
> +
> +	if (unlikely(in_interrupt() ||
> +			current->flags & (PF_KTHREAD | PF_EXITING)))
> +		return -EPERM;
> +
> +	if (unlikely(size != sizeof(struct bpf_pidns_info)))
> +		return -EINVAL;
> +
> +	pidns = task_active_pid_ns(current);
> +	if (unlikely(!pidns))
> +		return -ENOENT;
> +
> +	pidns_info->nsid =  pidns->ns.inum;
> +	pid = task_pid_nr_ns(current, pidns);
> +	if (unlikely(!pid))
> +		goto clear;
> +
> +	tgid = task_tgid_nr_ns(current, pidns);
> +	if (unlikely(!tgid))
> +		goto clear;
> +
> +	pidns_info->tgid = (u32) tgid;
> +	pidns_info->pid = (u32) pid;
> +
[...]
> +	fname = kmem_cache_alloc(names_cachep, GFP_ATOMIC);
> +	if (unlikely(!fname)) {
> +		ret = -ENOMEM;
> +		goto clear;
> +	}
> +	const size_t fnamesize = offsetof(struct filename, iname[1]);
> +	struct filename *tmp;
> +
> +	tmp = kmalloc(fnamesize, GFP_ATOMIC);
> +	if (unlikely(!tmp)) {
> +		__putname(fname);
> +		ret = -ENOMEM;
> +		goto clear;
> +	}
> +
> +	tmp->name = (char *)fname;
> +	fname = tmp;
> +	len = strlen(pidns_path) + 1;
> +	memcpy((char *)fname->name, pidns_path, len);
> +	fname->uptr = NULL;
> +	fname->aname = NULL;
> +	fname->refcnt = 1;
> +
> +	ret = filename_lookup(AT_FDCWD, fname, 0, &kp, NULL);
> +	if (ret)
> +		goto clear;
> +
> +	inode = d_backing_inode(kp.dentry);
> +	pidns_info->dev = (u32)inode->i_rdev;
The above can bee replaced with new nsfs interface function
ns_get_inum_dev().
> +
> +	return 0;
> +
> +clear:
> +	memset((void *)pidns_info, 0, (size_t) size);
> +	return ret;
> +}
> +
> +const struct bpf_func_proto bpf_get_current_pidns_info_proto = {
> +	.func		= bpf_get_current_pidns_info,
> +	.gpl_only	= false,
> +	.ret_type	= RET_INTEGER,
> +	.arg1_type	= ARG_PTR_TO_UNINIT_MEM,
> +	.arg2_type	= ARG_CONST_SIZE,
> +};
> +
>   #ifdef CONFIG_CGROUPS
>   BPF_CALL_0(bpf_get_current_cgroup_id)
>   {
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index ca1255d14576..5e1dc22765a5 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -709,6 +709,8 @@ tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>   #endif
>   	case BPF_FUNC_send_signal:
>   		return &bpf_send_signal_proto;
> +	case BPF_FUNC_get_current_pidns_info:
> +		return &bpf_get_current_pidns_info_proto;
>   	default:
>   		return NULL;
>   	}
>