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Date: Tue, 13 Aug 2019 23:51:14 +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: [Potential Spoof] Re: [PATCH bpf-next V9 1/3] bpf: new helper to
obtain namespace data from current task
On 8/13/19 4:11 PM, Yonghong Song wrote:
>
>
> 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;
A better condition is (from helper bpf_probe_write_user()):
if (unlikely(in_interrupt() ||
current->flags & (PF_KTHREAD | PF_EXITING)))
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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