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Wed, 09 Oct 2019 13:30:19 -0700 (PDT) Date: Wed, 9 Oct 2019 17:30:15 -0300 From: Carlos Antonio Neira Bustos To: Andrii Nakryiko Cc: Networking , Yonghong Song , ebiederm@xmission.com, Jesper Dangaard Brouer , bpf Subject: Re: [PATCH v13 2/4] bpf: added new helper bpf_get_ns_current_pid_tgid Message-ID: <20191009203015.GA14829@frodo.byteswizards.com> References: <20191009152632.14218-1-cneirabustos@gmail.com> <20191009152632.14218-3-cneirabustos@gmail.com> <20191009174538.GB12351@frodo.byteswizards.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.12.1 (2019-06-15) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Wed, Oct 09, 2019 at 12:50:10PM -0700, Andrii Nakryiko wrote: > On Wed, Oct 9, 2019 at 10:45 AM Carlos Antonio Neira Bustos > wrote: > > > > On Wed, Oct 09, 2019 at 09:14:42AM -0700, Andrii Nakryiko wrote: > > > On Wed, Oct 9, 2019 at 8:27 AM 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 > > > > --- > > > > include/linux/bpf.h | 1 + > > > > include/uapi/linux/bpf.h | 22 +++++++++++++++++++- > > > > kernel/bpf/core.c | 1 + > > > > kernel/bpf/helpers.c | 43 ++++++++++++++++++++++++++++++++++++++++ > > > > kernel/trace/bpf_trace.c | 2 ++ > > > > 5 files changed, 68 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..6ad3f2abf00d 100644 > > > > --- a/include/uapi/linux/bpf.h > > > > +++ b/include/uapi/linux/bpf.h > > > > @@ -2750,6 +2750,19 @@ 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(struct *bpf_pidns_info, u32 size) > > > > > > Should be: > > > > > > struct bpf_pidns_info *nsdata > > > > > > > + * Return > > > > + * 0 on success, values for pid and tgid from nsinfo will be as seen > > > > + * from the namespace that matches dev and inum from nsinfo. > > > > > > I think its cleaner to have a Description section, explaining that it > > > will return pid/tgid in bpf_pidns_info, and then describe exit codes > > > in Return section. > > > > > > > + * > > > > + * 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 +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_ns_current_pid_tgid), > > > > > > > > /* integer value in 'imm' field of BPF_CALL instruction selects which helper > > > > * function eBPF program intends to call > > > > @@ -3613,4 +3627,10 @@ struct bpf_sockopt { > > > > __s32 retval; > > > > }; > > > > > > > > +struct bpf_pidns_info { > > > > + __u64 dev; > > > > + __u64 inum; > > > > > > seems like conventionally this should be named "ino", this is what > > > ns_match calls it, so let's stay consistent. > > > > > > > + __u32 pid; > > > > + __u32 tgid; > > > > +}; > > > > > > So it seems like dev and inum are treated as input parameters, while > > > pid/tgid is output parameter, right? Wouldn't it be cleaner to have > > > dev and inum as explicit arguments into bpf_get_ns_current_pid_tgid()? > > > What's also not great, is that on failure you'll memset this entire > > > struct to zero, and user will lose its dev/inum. So in practice you'll > > > be keeping dev/inum somewhere else, then constructing and filling in > > > this bpf_pidns_info struct every time you need to invoke > > > bpf_get_ns_current_pid_tgid. > > > > > > Maybe it was discussed already, but IMO feels cleaner to have only > > > pid/tgid in bpf_pidns_info and pass dev/inum as direct arguments. > > > > > > > #endif /* _UAPI__LINUX_BPF_H__ */ > > > > 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..78a1ce7726aa 100644 > > > > --- a/kernel/bpf/helpers.c > > > > +++ b/kernel/bpf/helpers.c > > > > @@ -11,6 +11,8 @@ > > > > #include > > > > #include > > > > #include > > > > +#include > > > > +#include > > > > > > > > #include "../../lib/kstrtox.h" > > > > > > > > @@ -487,3 +489,44 @@ const struct bpf_func_proto bpf_strtoul_proto = { > > > > .arg4_type = ARG_PTR_TO_LONG, > > > > }; > > > > #endif > > > > + > > > > +BPF_CALL_2(bpf_get_ns_current_pid_tgid, struct bpf_pidns_info *, nsdata, u32, > > > > + size) > > > > +{ > > > > + struct task_struct *task = current; > > > > + struct pid_namespace *pidns; > > > > + int err = -EINVAL; > > > > + > > > > + if (unlikely(size != sizeof(struct bpf_pidns_info))) > > > > + goto clear; > > > > + > > > > + if ((u64)(dev_t)nsdata->dev != nsdata->dev) > > > > > > this seems unlikely() as well :) > > > > > > > + goto clear; > > > > + > > > > + if (unlikely(!task)) > > > > + goto clear; > > > > + > > > > + pidns = task_active_pid_ns(task); > > > > + if (unlikely(!pidns)) { > > > > + err = -ENOENT; > > > > + goto clear; > > > > + } > > > > + > > > > + if (!ns_match(&pidns->ns, (dev_t)nsdata->dev, nsdata->inum)) > > > > + goto clear; > > > > + > > > > + nsdata->pid = task_pid_nr_ns(task, pidns); > > > > + nsdata->tgid = task_tgid_nr_ns(task, pidns); > > > > + return 0; > > > > +clear: > > > > + memset((void *)nsdata, 0, (size_t) size); > > > > + return err; > > > > +} > > > > + > > > > +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_PTR_TO_UNINIT_MEM, > > > > > > So this is a lie, you do expect part of that struct to be initialized. > > > One more reason to just split off dev/inum(ino?). > > > > > > > > > > + .arg2_type = ARG_CONST_SIZE, > > > > +}; > > > > 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; > > > > } > > > > -- > > > > 2.20.1 > > > > > > Thanks for reviewing this, I'll make the changes you suggest. > > I'm not sure about removing dev and ino from struct bpf_pidns_info, I > > think is useful to know to which ns pid/tgid belong to using dev and ino > > to figure it out. Maybe in the future we could filter bpf_pidns_info > > structs by dev/ino, just an idea. > > I'm not following. dev/ino are specified by the caller to this helper, > right? So caller already know those values. With current set up, > though, the behavior is weird: this struct's dev/ino is preserved on > success, but zeroed out on failure, even though helper itself has > nothing to do with returning dev/ino. It also plays badly with > ARG_PTR_TO_UNINT_MEM, because that memory is expected to be at least > partially initialized. I see only downsides, to be honest. > > > > > Bests Andrii, Oh you are right dev/ino are specific to the caller of this helper, and what you state is correct dev/ino are also not returned by the caller based on that, yes this should be changed. Now I see the point, I'll change the helper to take dev/ino and just return pid/tgid. Thanks again!. Bests