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Date: Tue, 13 Aug 2019 23:11:14 +0000
From: Yonghong Song <yhs@...com>
To: Carlos Neira <cneirabustos@...il.com>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC: "ebiederm@...ssion.com" <ebiederm@...ssion.com>,
"brouer@...hat.com" <brouer@...hat.com>,
"bpf@...r.kernel.org" <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next V9 1/3] bpf: new helper to obtain namespace data
from current task
On 8/13/19 11:47 AM, Carlos Neira wrote:
> From: Carlos <cneirabustos@...il.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@...il.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(-)
>
> diff --git a/fs/internal.h b/fs/internal.h
> index 315fcd8d237c..6647e15dd419 100644
> --- a/fs/internal.h
> +++ b/fs/internal.h
> @@ -59,8 +59,6 @@ extern int finish_clean_context(struct fs_context *fc);
> /*
> * namei.c
> */
> -extern int filename_lookup(int dfd, struct filename *name, unsigned flags,
> - struct path *path, struct path *root);
> extern int user_path_mountpoint_at(int, const char __user *, unsigned int, struct path *);
> extern int vfs_path_lookup(struct dentry *, struct vfsmount *,
> const char *, unsigned int, struct path *);
> diff --git a/fs/namei.c b/fs/namei.c
> index 209c51a5226c..a89fc72a4a10 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -19,7 +19,6 @@
> #include <linux/export.h>
> #include <linux/kernel.h>
> #include <linux/slab.h>
> -#include <linux/fs.h>
> #include <linux/namei.h>
> #include <linux/pagemap.h>
> #include <linux/fsnotify.h>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index f9a506147c8a..e4adf5e05afd 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1050,6 +1050,7 @@ 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/linux/namei.h b/include/linux/namei.h
> index 9138b4471dbf..b45c8b6f7cb4 100644
> --- a/include/linux/namei.h
> +++ b/include/linux/namei.h
> @@ -6,6 +6,7 @@
> #include <linux/path.h>
> #include <linux/fcntl.h>
> #include <linux/errno.h>
> +#include <linux/fs.h>
>
> enum { MAX_NESTED_LINKS = 8 };
>
> @@ -97,6 +98,9 @@ extern void unlock_rename(struct dentry *, struct dentry *);
>
> extern void nd_jump_link(struct path *path);
>
> +extern int filename_lookup(int dfd, struct filename *name, unsigned flags,
> + struct path *path, struct path *root);
> +
> static inline void nd_terminate_link(void *name, size_t len, size_t maxlen)
> {
> ((char *) name)[min(len, maxlen)] = '\0';
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 4393bd4b2419..db241857ec15 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -2741,6 +2741,28 @@ 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
> + * Copies into *pidns* pid, namespace id and tgid as seen by the
> + * current namespace and also device from /proc/self/ns/pid.
> + * *size_of_pidns* must be the size of *pidns*
> + *
> + * This helper is used when pid filtering is needed inside a
> + * container as bpf_get_current_tgid() helper returns always the
> + * pid id as seen by the root namespace.
> + * Return
> + * 0 on success
> + *
> + * **-EINVAL** if *size_of_pidns* is not valid or unable to get ns, pid
> + * or tgid of the current task.
> + *
> + * **-ECHILD** if /proc/self/ns/pid does not exists.
> + *
> + * **-ENOTDIR** if /proc/self/ns does not exists.
> + *
> + * **-ENOMEM** if allocation fails.
> + *
> */
> #define __BPF_FUNC_MAPPER(FN) \
> FN(unspec), \
> @@ -2853,7 +2875,8 @@ 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
> @@ -3604,4 +3627,10 @@ struct bpf_sockopt {
> __s32 retval;
> };
>
> +struct bpf_pidns_info {
> + __u32 dev;
> + __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..41fbf1f28a48 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -11,6 +11,12 @@
> #include <linux/uidgid.h>
> #include <linux/filter.h>
> #include <linux/ctype.h>
> +#include <linux/pid_namespace.h>
> +#include <linux/major.h>
> +#include <linux/stat.h>
> +#include <linux/namei.h>
> +#include <linux/version.h>
> +
>
> #include "../../lib/kstrtox.h"
>
> @@ -312,6 +318,64 @@ 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 *tmp = NULL;
> + struct inode *inode;
> + struct path kp;
> + pid_t tgid = 0;
> + pid_t pid = 0;
> + int ret;
> + int len;
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);
> + if (unlikely(!pidns))
> + goto clear;
> + 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;
> + tmp = kmem_cache_alloc(names_cachep, GFP_ATOMIC);
> + if (unlikely(!tmp)) {
> + memset((void *)pidns_info, 0, (size_t) size);
> + return -ENOMEM;
> + }
> + len = strlen(pidns_path) + 1;
> + memcpy((char *)tmp->name, pidns_path, len);
> + tmp->uptr = NULL;
> + tmp->aname = NULL;
> + tmp->refcnt = 1;
> + ret = filename_lookup(AT_FDCWD, tmp, 0, &kp, NULL);
> + if (ret) {
> + memset((void *)pidns_info, 0, (size_t) size);
> + return ret;
> + }
> + inode = d_backing_inode(kp.dentry);
> + pidns_info->dev = inode->i_sb->s_dev;
> + return 0;
> +clear:
> + memset((void *)pidns_info, 0, (size_t) size);
> + return -EINVAL;
> +}
> +
> +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;
> }
>
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