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Date: Wed, 27 Dec 2017 15:18:14 -0800
From: Jakub Kicinski <jakub.kicinski@...ronome.com>
To: Daniel Borkmann <daniel@...earbox.net>
Cc: netdev@...r.kernel.org, alexei.starovoitov@...il.com,
ktkhai@...tuozzo.com, oss-drivers@...ronome.com,
"Eric W . Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH bpf-next v2 6/8] bpf: offload: report device information
for offloaded programs
On Wed, 27 Dec 2017 18:26:16 +0100, Daniel Borkmann wrote:
> On 12/21/2017 10:01 PM, Jakub Kicinski wrote:
> > Report to the user ifindex and namespace information of offloaded
> > programs. If device has disappeared return -ENODEV. Specify the
> > namespace using dev/inode combination.
> >
> > CC: Eric W. Biederman <ebiederm@...ssion.com>
> > Signed-off-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
> > Reviewed-by: Quentin Monnet <quentin.monnet@...ronome.com>
> > ---
> > v2:
> > - take RTNL lock to grab a coherent snapshot of device state
> > (ifindex vs name space) and avoid races with name space
> > moves (based on Eric's comment on Kirill's patch to
> > peernet2id_alloc()).
> > ---
> > fs/nsfs.c | 2 +-
> > include/linux/bpf.h | 2 ++
> > include/linux/proc_ns.h | 1 +
> > include/uapi/linux/bpf.h | 3 +++
> > kernel/bpf/offload.c | 44 ++++++++++++++++++++++++++++++++++++++++++
> > kernel/bpf/syscall.c | 6 ++++++
> > tools/include/uapi/linux/bpf.h | 3 +++
> > 7 files changed, 60 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/nsfs.c b/fs/nsfs.c
> > index 7c6f76d29f56..e50628675935 100644
> > --- a/fs/nsfs.c
> > +++ b/fs/nsfs.c
> > @@ -51,7 +51,7 @@ static void nsfs_evict(struct inode *inode)
> > ns->ops->put(ns);
> > }
> >
> > -static void *__ns_get_path(struct path *path, struct ns_common *ns)
> > +void *__ns_get_path(struct path *path, struct ns_common *ns)
> > {
> > struct vfsmount *mnt = nsfs_mnt;
> > struct dentry *dentry;
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index 9a916ab34299..7810ae57b357 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -531,6 +531,8 @@ static inline struct bpf_prog *bpf_prog_get_type(u32 ufd,
> >
> > int bpf_prog_offload_compile(struct bpf_prog *prog);
> > void bpf_prog_offload_destroy(struct bpf_prog *prog);
> > +int bpf_prog_offload_info_fill(struct bpf_prog_info *info,
> > + struct bpf_prog *prog);
> >
> > #if defined(CONFIG_NET) && defined(CONFIG_BPF_SYSCALL)
> > int bpf_prog_offload_init(struct bpf_prog *prog, union bpf_attr *attr);
> > diff --git a/include/linux/proc_ns.h b/include/linux/proc_ns.h
> > index 2ff18c9840a7..1733359cf713 100644
> > --- a/include/linux/proc_ns.h
> > +++ b/include/linux/proc_ns.h
> > @@ -76,6 +76,7 @@ static inline int ns_alloc_inum(struct ns_common *ns)
> >
> > extern struct file *proc_ns_fget(int fd);
> > #define get_proc_ns(inode) ((struct ns_common *)(inode)->i_private)
> > +extern void *__ns_get_path(struct path *path, struct ns_common *ns);
> > extern void *ns_get_path(struct path *path, struct task_struct *task,
> > const struct proc_ns_operations *ns_ops);
> >
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index d01f1cb3cfc0..72b37fc3bc0c 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -921,6 +921,9 @@ struct bpf_prog_info {
> > __u32 nr_map_ids;
> > __aligned_u64 map_ids;
> > char name[BPF_OBJ_NAME_LEN];
> > + __u32 ifindex;
> > + __u64 netns_dev;
> > + __u64 netns_ino;
> > } __attribute__((aligned(8)));
> >
> > struct bpf_map_info {
> > diff --git a/kernel/bpf/offload.c b/kernel/bpf/offload.c
> > index 1e6064ea3609..4d50000bd1e3 100644
> > --- a/kernel/bpf/offload.c
> > +++ b/kernel/bpf/offload.c
> > @@ -16,9 +16,11 @@
> > #include <linux/bpf.h>
> > #include <linux/bpf_verifier.h>
> > #include <linux/bug.h>
> > +#include <linux/kdev_t.h>
> > #include <linux/list.h>
> > #include <linux/netdevice.h>
> > #include <linux/printk.h>
> > +#include <linux/proc_ns.h>
> > #include <linux/rtnetlink.h>
> > #include <linux/rwsem.h>
> >
> > @@ -181,6 +183,48 @@ int bpf_prog_offload_compile(struct bpf_prog *prog)
> > return bpf_prog_offload_translate(prog);
> > }
> >
> > +int bpf_prog_offload_info_fill(struct bpf_prog_info *info,
> > + struct bpf_prog *prog)
> > +{
> > + struct bpf_dev_offload *offload;
> > + struct inode *ns_inode;
> > + struct path ns_path;
> > + int ifindex, err;
> > + struct net *net;
> > +
> > +again:
> > + rtnl_lock();
> > + down_read(&bpf_devs_lock);
> > +
> > + offload = prog->aux->offload;
> > + if (!offload) {
> > + up_read(&bpf_devs_lock);
> > + rtnl_unlock();
> > + return -ENODEV;
> > + }
> > +
> > + ifindex = offload->netdev->ifindex;
> > + net = dev_net(offload->netdev);
> > + get_net(net); /* __ns_get_path() drops the reference */
> > +
> > + up_read(&bpf_devs_lock);
> > + rtnl_unlock();
> > +
> > + err = PTR_ERR_OR_ZERO(__ns_get_path(&ns_path, &net->ns));
> > + if (err) {
> > + if (err == -EAGAIN)
> > + goto again;
> > + return err;
> > + }
> > + ns_inode = ns_path.dentry->d_inode;
> > +
> > + info->ifindex = ifindex;
> > + info->netns_dev = new_encode_dev(ns_inode->i_sb->s_dev);
> > + info->netns_ino = ns_inode->i_ino;
>
> I think here, we're still missing a:
>
> path_put(&ns_path);
>
> Otherwise we're leaking that reference, no?
You're right. Thanks for the detailed suggestion, let me try to meld
it into this series.
> Looking at perf, it does similar fetch of dev/ino pair through
> perf_fill_ns_link_info(). Only difference is that task / ns_ops
> are used to lookup the actual ns from a task, which we already
> have in our case (netns) through netdev.
>
> I've been thinking, could we make this more generic and move the
> bits into fs/nsfs.c by having the retry itself in ns_get_path_cb()?
>
> What I mean is:
>
> void *ns_get_path_cb(struct path *path, ns_get_path_helper_t *ns_get_cb,
> void *private_data)
> {
> struct ns_common *ns;
> void *ret;
>
> again:
> ns = ns_get_cb(private_data);
> if (!ns)
> return ERR_PTR(-ENOENT);
>
> ret = __ns_get_path(path, ns);
> if (IS_ERR(ret) && PTR_ERR(ret) == -EAGAIN)
> goto again;
> return ret;
> }
>
> And then in bpf_prog_offload_info_fill(), we can just move the fetching
> and holding ref of net into the callback and do something similar to:
>
> struct path ns_path;
> struct inode *ns_inode;
> struct cb_info = {
> .offload = prog->aux->offload,
> .info = info,
> };
> void *ret;
>
> ret = ns_get_path_cb(&ns_path, bpf_prog_offload_get_cb, &cb_info);
> if (!ret) {
> ns_inode = ns_path.dentry->d_inode;
> info->netns_dev = new_encode_dev(ns_inode->i_sb->s_dev);
> info->netns_ino = ns_inode->i_ino;
> path_put(&ns_path);
> }
>
> And bpf_prog_offload_get_cb() would either return &net->ns in case
> of valid offload and can fill in the ifindex into info since we hold
> rtnl there, or otherwise return NULL, so we get -ENOENT back.
>
> This would allow to keep __ns_get_path() (including retry) private and
> have a more generic, reusable API similar to ns_get_path() that just
> has a cb for getting ns_common.
>
> (Rest of the series with feedback from Kirill included looks good to me.)
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