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22d917d80e
- Convert the old uid mapping functions into compatibility wrappers
- Add a uid/gid mapping layer from user space uid and gids to kernel
internal uids and gids that is extent based for simplicty and speed.
* Working with number space after mapping uids/gids into their kernel
internal version adds only mapping complexity over what we have today,
leaving the kernel code easy to understand and test.
- Add proc files /proc/self/uid_map /proc/self/gid_map
These files display the mapping and allow a mapping to be added
if a mapping does not exist.
- Allow entering the user namespace without a uid or gid mapping.
Since we are starting with an existing user our uids and gids
still have global mappings so are still valid and useful they just don't
have local mappings. The requirement for things to work are global uid
and gid so it is odd but perfectly fine not to have a local uid
and gid mapping.
Not requiring global uid and gid mappings greatly simplifies
the logic of setting up the uid and gid mappings by allowing
the mappings to be set after the namespace is created which makes the
slight weirdness worth it.
- Make the mappings in the initial user namespace to the global
uid/gid space explicit. Today it is an identity mapping
but in the future we may want to twist this for debugging, similar
to what we do with jiffies.
- Document the memory ordering requirements of setting the uid and
gid mappings. We only allow the mappings to be set once
and there are no pointers involved so the requirments are
trivial but a little atypical.
Performance:
In this scheme for the permission checks the performance is expected to
stay the same as the actuall machine instructions should remain the same.
The worst case I could think of is ls -l on a large directory where
all of the stat results need to be translated with from kuids and
kgids to uids and gids. So I benchmarked that case on my laptop
with a dual core hyperthread Intel i5-2520M cpu with 3M of cpu cache.
My benchmark consisted of going to single user mode where nothing else
was running. On an ext4 filesystem opening 1,000,000 files and looping
through all of the files 1000 times and calling fstat on the
individuals files. This was to ensure I was benchmarking stat times
where the inodes were in the kernels cache, but the inode values were
not in the processors cache. My results:
v3.4-rc1: ~= 156ns (unmodified v3.4-rc1 with user namespace support disabled)
v3.4-rc1-userns-: ~= 155ns (v3.4-rc1 with my user namespace patches and user namespace support disabled)
v3.4-rc1-userns+: ~= 164ns (v3.4-rc1 with my user namespace patches and user namespace support enabled)
All of the configurations ran in roughly 120ns when I performed tests
that ran in the cpu cache.
So in summary the performance impact is:
1ns improvement in the worst case with user namespace support compiled out.
8ns aka 5% slowdown in the worst case with user namespace support compiled in.
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
200 lines
4.2 KiB
C
200 lines
4.2 KiB
C
#ifndef _LINUX_UIDGID_H
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#define _LINUX_UIDGID_H
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/*
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* A set of types for the internal kernel types representing uids and gids.
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*
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* The types defined in this header allow distinguishing which uids and gids in
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* the kernel are values used by userspace and which uid and gid values are
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* the internal kernel values. With the addition of user namespaces the values
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* can be different. Using the type system makes it possible for the compiler
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* to detect when we overlook these differences.
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*
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*/
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#include <linux/types.h>
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#include <linux/highuid.h>
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struct user_namespace;
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extern struct user_namespace init_user_ns;
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#ifdef CONFIG_UIDGID_STRICT_TYPE_CHECKS
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typedef struct {
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uid_t val;
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} kuid_t;
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typedef struct {
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gid_t val;
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} kgid_t;
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#define KUIDT_INIT(value) (kuid_t){ value }
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#define KGIDT_INIT(value) (kgid_t){ value }
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static inline uid_t __kuid_val(kuid_t uid)
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{
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return uid.val;
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}
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static inline gid_t __kgid_val(kgid_t gid)
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{
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return gid.val;
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}
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#else
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typedef uid_t kuid_t;
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typedef gid_t kgid_t;
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static inline uid_t __kuid_val(kuid_t uid)
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{
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return uid;
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}
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static inline gid_t __kgid_val(kgid_t gid)
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{
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return gid;
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}
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#define KUIDT_INIT(value) ((kuid_t) value )
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#define KGIDT_INIT(value) ((kgid_t) value )
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#endif
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#define GLOBAL_ROOT_UID KUIDT_INIT(0)
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#define GLOBAL_ROOT_GID KGIDT_INIT(0)
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#define INVALID_UID KUIDT_INIT(-1)
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#define INVALID_GID KGIDT_INIT(-1)
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static inline bool uid_eq(kuid_t left, kuid_t right)
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{
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return __kuid_val(left) == __kuid_val(right);
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}
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static inline bool gid_eq(kgid_t left, kgid_t right)
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{
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return __kgid_val(left) == __kgid_val(right);
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}
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static inline bool uid_gt(kuid_t left, kuid_t right)
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{
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return __kuid_val(left) > __kuid_val(right);
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}
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static inline bool gid_gt(kgid_t left, kgid_t right)
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{
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return __kgid_val(left) > __kgid_val(right);
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}
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static inline bool uid_gte(kuid_t left, kuid_t right)
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{
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return __kuid_val(left) >= __kuid_val(right);
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}
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static inline bool gid_gte(kgid_t left, kgid_t right)
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{
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return __kgid_val(left) >= __kgid_val(right);
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}
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static inline bool uid_lt(kuid_t left, kuid_t right)
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{
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return __kuid_val(left) < __kuid_val(right);
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}
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static inline bool gid_lt(kgid_t left, kgid_t right)
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{
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return __kgid_val(left) < __kgid_val(right);
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}
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static inline bool uid_lte(kuid_t left, kuid_t right)
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{
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return __kuid_val(left) <= __kuid_val(right);
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}
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static inline bool gid_lte(kgid_t left, kgid_t right)
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{
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return __kgid_val(left) <= __kgid_val(right);
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}
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static inline bool uid_valid(kuid_t uid)
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{
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return !uid_eq(uid, INVALID_UID);
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}
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static inline bool gid_valid(kgid_t gid)
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{
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return !gid_eq(gid, INVALID_GID);
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}
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#ifdef CONFIG_USER_NS
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extern kuid_t make_kuid(struct user_namespace *from, uid_t uid);
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extern kgid_t make_kgid(struct user_namespace *from, gid_t gid);
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extern uid_t from_kuid(struct user_namespace *to, kuid_t uid);
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extern gid_t from_kgid(struct user_namespace *to, kgid_t gid);
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extern uid_t from_kuid_munged(struct user_namespace *to, kuid_t uid);
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extern gid_t from_kgid_munged(struct user_namespace *to, kgid_t gid);
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static inline bool kuid_has_mapping(struct user_namespace *ns, kuid_t uid)
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{
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return from_kuid(ns, uid) != (uid_t) -1;
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}
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static inline bool kgid_has_mapping(struct user_namespace *ns, kgid_t gid)
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{
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return from_kgid(ns, gid) != (gid_t) -1;
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}
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#else
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static inline kuid_t make_kuid(struct user_namespace *from, uid_t uid)
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{
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return KUIDT_INIT(uid);
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}
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static inline kgid_t make_kgid(struct user_namespace *from, gid_t gid)
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{
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return KGIDT_INIT(gid);
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}
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static inline uid_t from_kuid(struct user_namespace *to, kuid_t kuid)
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{
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return __kuid_val(kuid);
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}
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static inline gid_t from_kgid(struct user_namespace *to, kgid_t kgid)
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{
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return __kgid_val(kgid);
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}
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static inline uid_t from_kuid_munged(struct user_namespace *to, kuid_t kuid)
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{
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uid_t uid = from_kuid(to, kuid);
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if (uid == (uid_t)-1)
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uid = overflowuid;
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return uid;
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}
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static inline gid_t from_kgid_munged(struct user_namespace *to, kgid_t kgid)
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{
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gid_t gid = from_kgid(to, kgid);
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if (gid == (gid_t)-1)
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gid = overflowgid;
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return gid;
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}
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static inline bool kuid_has_mapping(struct user_namespace *ns, kuid_t uid)
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{
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return true;
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}
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static inline bool kgid_has_mapping(struct user_namespace *ns, kgid_t gid)
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{
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return true;
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}
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#endif /* CONFIG_USER_NS */
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#endif /* _LINUX_UIDGID_H */
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