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Subject[PATCH bpf 2/4] nsfs: add an ioctl to discover the network namespace cookie
Date
Network namespaces have a globally unique non-zero identifier aka a
cookie, in line with socket cookies. Add an ioctl to retrieve the
cookie from user space without going via BPF.

Cc: linux-api@vger.kernel.org
Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
---
fs/nsfs.c | 9 +++++++++
include/net/net_namespace.h | 11 +++++++++++
include/uapi/linux/nsfs.h | 2 ++
3 files changed, 22 insertions(+)

diff --git a/fs/nsfs.c b/fs/nsfs.c
index 800c1d0eb0d0..d7865e39c049 100644
--- a/fs/nsfs.c
+++ b/fs/nsfs.c
@@ -11,6 +11,7 @@
#include <linux/user_namespace.h>
#include <linux/nsfs.h>
#include <linux/uaccess.h>
+#include <net/net_namespace.h>

#include "internal.h"

@@ -191,6 +192,8 @@ static long ns_ioctl(struct file *filp, unsigned int ioctl,
struct user_namespace *user_ns;
struct ns_common *ns = get_proc_ns(file_inode(filp));
uid_t __user *argp;
+ struct net *net_ns;
+ u64 cookie;
uid_t uid;

switch (ioctl) {
@@ -209,6 +212,12 @@ static long ns_ioctl(struct file *filp, unsigned int ioctl,
argp = (uid_t __user *) arg;
uid = from_kuid_munged(current_user_ns(), user_ns->owner);
return put_user(uid, argp);
+ case NS_GET_COOKIE:
+ if (ns->ops->type != CLONE_NEWNET)
+ return -EINVAL;
+ net_ns = container_of(ns, struct net, ns);
+ cookie = net_gen_cookie(net_ns);
+ return put_user(cookie, (u64 __user *)arg);
default:
return -ENOTTY;
}
diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index 29567875f428..bbd22dfa9345 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -226,6 +226,17 @@ struct net *get_net_ns_by_fd(int fd);

u64 __net_gen_cookie(struct net *net);

+static inline u64 net_gen_cookie(struct net *net)
+{
+ u64 cookie;
+
+ preempt_disable();
+ cookie = __net_gen_cookie(net);
+ preempt_enable();
+
+ return cookie;
+}
+
#ifdef CONFIG_SYSCTL
void ipx_register_sysctl(void);
void ipx_unregister_sysctl(void);
diff --git a/include/uapi/linux/nsfs.h b/include/uapi/linux/nsfs.h
index a0c8552b64ee..86611c2cf908 100644
--- a/include/uapi/linux/nsfs.h
+++ b/include/uapi/linux/nsfs.h
@@ -15,5 +15,7 @@
#define NS_GET_NSTYPE _IO(NSIO, 0x3)
/* Get owner UID (in the caller's user namespace) for a user namespace */
#define NS_GET_OWNER_UID _IO(NSIO, 0x4)
+/* Returns a unique non-zero identifier for a network namespace */
+#define NS_GET_COOKIE _IO(NSIO, 0x5)

#endif /* __LINUX_NSFS_H */
--
2.27.0
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