Add a helper to easily check whether a given namespace is the caller's
current namespace. This is currently open-coded in a lot of places.
Simply switch on the type and compare the results.

Reviewed-by: Aleksa Sarai <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
---
 include/linux/nsfs.h | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/include/linux/nsfs.h b/include/linux/nsfs.h
index fb84aa538091..e5a5fa83d36b 100644
--- a/include/linux/nsfs.h
+++ b/include/linux/nsfs.h
@@ -5,6 +5,8 @@
 #define _LINUX_NSFS_H
 
 #include <linux/ns_common.h>
+#include <linux/cred.h>
+#include <linux/pid_namespace.h>
 
 struct path;
 struct task_struct;
@@ -22,5 +24,17 @@ int ns_get_name(char *buf, size_t size, struct task_struct 
*task,
                        const struct proc_ns_operations *ns_ops);
 void nsfs_init(void);
 
-#endif /* _LINUX_NSFS_H */
+#define __current_namespace_from_type(__ns)                            \
+       _Generic((__ns),                                                \
+               struct cgroup_namespace *: current->nsproxy->cgroup_ns, \
+               struct ipc_namespace *:    current->nsproxy->ipc_ns,    \
+               struct net *:              current->nsproxy->net_ns,    \
+               struct pid_namespace *:    task_active_pid_ns(current), \
+               struct mnt_namespace *:    current->nsproxy->mnt_ns,    \
+               struct time_namespace *:   current->nsproxy->time_ns,   \
+               struct user_namespace *:   current_user_ns(),           \
+               struct uts_namespace *:    current->nsproxy->uts_ns)
+
+#define current_in_namespace(__ns) (__current_namespace_from_type(__ns) == 
__ns)
 
+#endif /* _LINUX_NSFS_H */

-- 
2.47.3


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