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user_ns: Introduce user_nsmap_uid and user_ns_map_gid.

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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>
This commit is contained in:
Eric W. Biederman 2010-06-13 03:28:03 +00:00 committed by David S. Miller
parent 812e876e84
commit 5c1469de75
2 changed files with 58 additions and 0 deletions
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14
include/linux/user_namespace.h
View File

@ -36,6 +36,9 @@ static inline void put_user_ns(struct user_namespace *ns)
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 user_namespace *ns)
{
}
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 */

44
kernel/user_namespace.c
View File

@ -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;
}