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Subject[PATCH] [56/139] user_ns: Introduce user_nsmap_uid and user_ns_map_gid.
Date
2.6.35-longterm review patch.  If anyone has any objections, please let me know.

------------------
Upstream commit 5c1469de7545a35a16ff2b902e217044a7d2f8a5
Define what happens when a we view a uid from one user_namespace
in another user_namepece.

- If the user namespaces are the same no mapping is necessary.

- For most cases of difference use overflowuid and overflowgid,
the uid and gid currently used for 16bit apis when we have a 32bit uid
that does fit in 16bits. Effectively the situation is the same,
we want to return a uid or gid that is not assigned to any user.

- For the case when we happen to be mapping the uid or gid of the
creator of the target user namespace use uid 0 and gid as confusing
that user with root is not a problem.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Acked-by: Serge E. Hallyn <serue@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

Index: linux-2.6.35.y/include/linux/user_namespace.h
===================================================================
--- linux-2.6.35.y.orig/include/linux/user_namespace.h
+++ linux-2.6.35.y/include/linux/user_namespace.h
@@ -36,6 +36,9 @@ static inline void put_user_ns(struct us
kref_put(&ns->kref, free_user_ns);
}

+uid_t user_ns_map_uid(struct user_namespace *to, const struct cred *cred, uid_t uid);
+gid_t user_ns_map_gid(struct user_namespace *to, const struct cred *cred, gid_t gid);
+
#else

static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
@@ -52,6 +55,17 @@ static inline void put_user_ns(struct us
{
}

+static inline uid_t user_ns_map_uid(struct user_namespace *to,
+ const struct cred *cred, uid_t uid)
+{
+ return uid;
+}
+static inline gid_t user_ns_map_gid(struct user_namespace *to,
+ const struct cred *cred, gid_t gid)
+{
+ return gid;
+}
+
#endif

#endif /* _LINUX_USER_H */
Index: linux-2.6.35.y/kernel/user_namespace.c
===================================================================
--- linux-2.6.35.y.orig/kernel/user_namespace.c
+++ linux-2.6.35.y/kernel/user_namespace.c
@@ -9,6 +9,7 @@
#include <linux/nsproxy.h>
#include <linux/slab.h>
#include <linux/user_namespace.h>
+#include <linux/highuid.h>
#include <linux/cred.h>

/*
@@ -82,3 +83,46 @@ void free_user_ns(struct kref *kref)
schedule_work(&ns->destroyer);
}
EXPORT_SYMBOL(free_user_ns);
+
+uid_t user_ns_map_uid(struct user_namespace *to, const struct cred *cred, uid_t uid)
+{
+ struct user_namespace *tmp;
+
+ if (likely(to == cred->user->user_ns))
+ return uid;
+
+
+ /* Is cred->user the creator of the target user_ns
+ * or the creator of one of it's parents?
+ */
+ for ( tmp = to; tmp != &init_user_ns;
+ tmp = tmp->creator->user_ns ) {
+ if (cred->user == tmp->creator) {
+ return (uid_t)0;
+ }
+ }
+
+ /* No useful relationship so no mapping */
+ return overflowuid;
+}
+
+gid_t user_ns_map_gid(struct user_namespace *to, const struct cred *cred, gid_t gid)
+{
+ struct user_namespace *tmp;
+
+ if (likely(to == cred->user->user_ns))
+ return gid;
+
+ /* Is cred->user the creator of the target user_ns
+ * or the creator of one of it's parents?
+ */
+ for ( tmp = to; tmp != &init_user_ns;
+ tmp = tmp->creator->user_ns ) {
+ if (cred->user == tmp->creator) {
+ return (gid_t)0;
+ }
+ }
+
+ /* No useful relationship so no mapping */
+ return overflowgid;
+}

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