nsfs: generalize ns_get_path() for path resolution with a task

ns_get_path() takes struct task_struct and proc_ns_ops as its
parameters.  For path resolution directly from a namespace,
e.g. based on a networking device's net name space, we need
more flexibility.  Add a ns_get_path_cb() helper which will
allow callers to use any method of obtaining the name space
reference.  Convert ns_get_path() to use ns_get_path_cb().

Following patches will bring a networking user.

CC: Eric W. Biederman <ebiederm@xmission.com>
Suggested-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

2 files changed, 29 insertions, 3 deletions

diff --git a/fs/nsfs.c b/fs/nsfs.c
index 7c6f76d29f56..36b0772701a0 100644
--- a/fs/nsfs.c
+++ b/fs/nsfs.c
@@ -103,14 +103,14 @@ slow:
         goto got_it;
 }
 
-void *ns_get_path(struct path *path, struct task_struct *task,
-                        const struct proc_ns_operations *ns_ops)
+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_ops->get(task);
+        ns = ns_get_cb(private_data);
         if (!ns)
                 return ERR_PTR(-ENOENT);
 
@@ -120,6 +120,29 @@ again:
         return ret;
 }
 
+struct ns_get_path_task_args {
+        const struct proc_ns_operations *ns_ops;
+        struct task_struct *task;
+};
+
+static struct ns_common *ns_get_path_task(void *private_data)
+{
+        struct ns_get_path_task_args *args = private_data;
+
+        return args->ns_ops->get(args->task);
+}
+
+void *ns_get_path(struct path *path, struct task_struct *task,
+                  const struct proc_ns_operations *ns_ops)
+{
+        struct ns_get_path_task_args args = {
+                .ns_ops = ns_ops,
+                .task   = task,
+        };
+
+        return ns_get_path_cb(path, ns_get_path_task, &args);
+}
+
 int open_related_ns(struct ns_common *ns,
                    struct ns_common *(*get_ns)(struct ns_common *ns))
 {
diff --git a/include/linux/proc_ns.h b/include/linux/proc_ns.h
index 2ff18c9840a7..d31cb6215905 100644
--- a/include/linux/proc_ns.h
+++ b/include/linux/proc_ns.h
@@ -78,6 +78,9 @@ 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 task_struct *task,
                         const struct proc_ns_operations *ns_ops);
+typedef struct ns_common *ns_get_path_helper_t(void *);
+extern void *ns_get_path_cb(struct path *path, ns_get_path_helper_t ns_get_cb,
+                            void *private_data);
 
 extern int ns_get_name(char *buf, size_t size, struct task_struct *task,
                         const struct proc_ns_operations *ns_ops);