On Wed, Oct 02, 2019 at 12:52:29PM +0200, Daniel Borkmann wrote:
> On 10/1/19 11:41 PM, Carlos Neira 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 <cneirabus...@gmail.com>
> > ---
> > include/linux/bpf.h | 1 +
> > include/uapi/linux/bpf.h | 18 +++++++++++++++++-
> > kernel/bpf/core.c | 1 +
> > kernel/bpf/helpers.c | 36 ++++++++++++++++++++++++++++++++++++
> > kernel/trace/bpf_trace.c | 2 ++
> > 5 files changed, 57 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..ea8145d7f897 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
> > + *
> > + * u64 bpf_get_ns_current_pid_tgid(u64 dev, u64 inum)
> > + * Return
> > + * A 64-bit integer containing the current tgid and pid from
> > current task
> > + * 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, or if dev conversion to dev_t
> > lost high bits.
> > + *
> > + * **-ENOENT** if /proc/self/ns does not exists.
> > + *
> > */
> > #define __BPF_FUNC_MAPPER(FN) \
> > FN(unspec), \
> > @@ -2862,7 +2877,8 @@ union bpf_attr {
> > FN(sk_storage_get), \
> > FN(sk_storage_delete), \
> > FN(send_signal), \
> > - FN(tcp_gen_syncookie),
> > + FN(tcp_gen_syncookie), \
> > + FN(get_ns_current_pid_tgid),
> > /* integer value in 'imm' field of BPF_CALL instruction selects which
> > helper
> > * function eBPF program intends to call
> > diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> > index 66088a9e9b9e..b2fd5358f472 100644
> > --- a/kernel/bpf/core.c
> > +++ b/kernel/bpf/core.c
> > @@ -2042,6 +2042,7 @@ 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_ns_current_pid_tgid_proto __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..8777181d1717 100644
> > --- a/kernel/bpf/helpers.c
> > +++ b/kernel/bpf/helpers.c
> > @@ -11,6 +11,8 @@
> > #include <linux/uidgid.h>
> > #include <linux/filter.h>
> > #include <linux/ctype.h>
> > +#include <linux/pid_namespace.h>
> > +#include <linux/proc_ns.h>
> > #include "../../lib/kstrtox.h"
> > @@ -487,3 +489,37 @@ const struct bpf_func_proto bpf_strtoul_proto = {
> > .arg4_type = ARG_PTR_TO_LONG,
> > };
> > #endif
> > +
> > +BPF_CALL_2(bpf_get_ns_current_pid_tgid, u64, dev, u64, inum)
> > +{
> > + struct task_struct *task = current;
> > + struct pid_namespace *pidns;
> > + pid_t pid, tgid;
> > +
> > + if ((u64)(dev_t)dev != dev)
> > + return -EINVAL;
> > +
> > + if (unlikely(!task))
> > + return -EINVAL;
> > +
> > + pidns = task_active_pid_ns(task);
> > + if (unlikely(!pidns))
> > + return -ENOENT;
> > +
> > +
> > + if (!ns_match(&pidns->ns, (dev_t)dev, inum))
> > + return -EINVAL;
> > +
> > + pid = task_pid_nr_ns(task, pidns);
> > + tgid = task_tgid_nr_ns(task, pidns);
> > +
> > + return (u64) tgid << 32 | pid;
>
> Basically here you are overlapping the 64-bit return value for the valid
> outcome with the error codes above for the invalid case. If you look at
> bpf_perf_event_read() we already had such broken occasion that bit us in
> the past, and needed to introduce bpf_perf_event_read_value() instead.
> Lets not go there again and design it similarly to the latter.
>
> > +}
> > +
> > +const struct bpf_func_proto bpf_get_ns_current_pid_tgid_proto = {
> > + .func = bpf_get_ns_current_pid_tgid,
> > + .gpl_only = false,
> > + .ret_type = RET_INTEGER,
> > + .arg1_type = ARG_ANYTHING,
> > + .arg2_type = ARG_ANYTHING,
> > +};
> > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > index 44bd08f2443b..32331a1dcb6d 100644
> > --- a/kernel/trace/bpf_trace.c
> > +++ b/kernel/trace/bpf_trace.c
> > @@ -735,6 +735,8 @@ 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_ns_current_pid_tgid:
> > + return &bpf_get_ns_current_pid_tgid_proto;
> > default:
> > return NULL;
> > }
> >
>
Daniel,
If I understand correctly, to avoid problems I need to change the helper's
function signature to something like the following:
struct bpf_ns_current_pid_tgid_storage {
__u64 dev;
__u64 inum;
__u64 pidtgid;
};
BPF_CALL_2(bpf_get_ns_current_pid_tgid,
struct bpf_ns_current_pid_tgid_storage *, buf, u32, size);
then use dev and inum provided by the user and return the requested
value into pidtgid of the struct. Would that work?
Thanks for your help.
