Introduces new vfs{g,u}id_t types. Similar to k{g,u}id_t the new types
are just simple wrapper structs around regular {g,u}id_t types.
They allows to establish a type safety boundary between {g,u}ids on
idmapped mounts and {g,u}ids as they are represented in filesystems
themselves.
A vfs{g,u}id_t is always created from a k{g,u}id_t, never directly from
a {g,u}id_t as idmapped mounts remap a given {g,u}id according to the
mount's idmapping. This is expressed in the VFS{G,U}IDT_INIT() macros.
A vfs{g,u}id_t may be used as a k{g,u}id_t via AS_K{G,U}IDT(). This
often happens when we need to check whether a {g,u}id mapped according
to an idmapped mount is identical to a given k{g,u}id_t. For an example,
see vfsgid_in_group_p() which determines whether the value of vfsgid_t
matches the value of any of the caller's groups. Similar logic is
expressed in the k{g,u}id_eq_vfs{g,u}id().
The vfs{g,u}id_to_k{g,u}id() helpers map a given vfs{g,u}id_t from the
mount's idmapping into the filesystem idmapping. They make it possible
to update a filesystem object such as inode->i_{g,u}id with the correct
value.
This makes it harder to accidently write a wrong {g,u}id anwywhere. The
vfs{g,u}id_has_mapping() helpers check whether a given vfs{g,u}id_t can
be represented in the filesystem idmapping.
All new helpers are nops on non-idmapped mounts.
I've done work on this roughly 7 months ago but dropped it to focus on
the testsuite. Linus brought this up independently just last week and
it's time to move this along (see [1]).
[1]: https://lore.kernel.org/lkml/CAHk-=win6+ahs1EwLkcq8apqLi_1wXFWbrPf340zYEhObpz4jA@xxxxxxxxxxxxxx
Cc: Seth Forshee <sforshee@xxxxxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Aleksa Sarai <cyphar@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
CC: linux-fsdevel@xxxxxxxxxxxxxxx
Signed-off-by: Christian Brauner (Microsoft) <brauner@xxxxxxxxxx>
---
/* v2 */
- Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>:
- Rename s/kmnt{g,u}id_t/vfs{g,u}id_t/g
---
include/linux/mnt_idmapping.h | 190 ++++++++++++++++++++++++++++++++++
1 file changed, 190 insertions(+)
diff --git a/include/linux/mnt_idmapping.h b/include/linux/mnt_idmapping.h
index ee5a217de2a8..241e94663930 100644
--- a/include/linux/mnt_idmapping.h
+++ b/include/linux/mnt_idmapping.h
@@ -13,6 +13,122 @@ struct user_namespace;
*/
extern struct user_namespace init_user_ns;
+typedef struct {
+ uid_t val;
+} vfsuid_t;
+
+typedef struct {
+ gid_t val;
+} vfsgid_t;
+
+#ifdef CONFIG_MULTIUSER
+static inline uid_t __vfsuid_val(vfsuid_t uid)
+{
+ return uid.val;
+}
+
+static inline gid_t __vfsgid_val(vfsgid_t gid)
+{
+ return gid.val;
+}
+#else
+static inline uid_t __vfsuid_val(vfsuid_t uid)
+{
+ return 0;
+}
+
+static inline gid_t __vfsgid_val(vfsgid_t gid)
+{
+ return 0;
+}
+#endif
+
+static inline bool vfsuid_valid(vfsuid_t uid)
+{
+ return __vfsuid_val(uid) != (uid_t)-1;
+}
+
+static inline bool vfsgid_valid(vfsgid_t gid)
+{
+ return __vfsgid_val(gid) != (gid_t)-1;
+}
+
+/**
+ * kuid_eq_vfsuid - check whether kuid and vfsuid have the same value
+ * @kuid: the kuid to compare
+ * @vfsuid: the vfsuid to compare
+ *
+ * Check whether @kuid and @vfsuid have the same values.
+ *
+ * Return: true if @kuid and @vfsuid have the same value, false if not.
+ */
+static inline bool kuid_eq_vfsuid(kuid_t kuid, vfsuid_t vfsuid)
+{
+ return __vfsuid_val(vfsuid) == __kuid_val(kuid);
+}
+
+/**
+ * kgid_eq_vfsgid - check whether kgid and vfsgid have the same value
+ * @kgid: the kgid to compare
+ * @vfsgid: the vfsgid to compare
+ *
+ * Check whether @kgid and @vfsgid have the same values.
+ *
+ * Return: true if @kgid and @vfsgid have the same value, false if not.
+ */
+static inline bool kgid_eq_vfsgid(kgid_t kgid, vfsgid_t vfsgid)
+{
+ return __vfsgid_val(vfsgid) == __kgid_val(kgid);
+}
+
+static inline bool vfsuid_eq(vfsuid_t left, vfsuid_t right)
+{
+ return __vfsuid_val(left) == __vfsuid_val(right);
+}
+
+static inline bool vfsgid_eq(vfsgid_t left, vfsgid_t right)
+{
+ return __vfsgid_val(left) == __vfsgid_val(right);
+}
+
+/*
+ * vfs{g,u}ids are created from k{g,u}ids.
+ * We don't allow them to be created from regular {u,g}id.
+ */
+#define VFSUIDT_INIT(val) (vfsuid_t){ __kuid_val(val) }
+#define VFSGIDT_INIT(val) (vfsgid_t){ __kgid_val(val) }
+
+#define INVALID_VFSUID VFSUIDT_INIT(INVALID_UID)
+#define INVALID_VFSGID VFSGIDT_INIT(INVALID_GID)
+
+/*
+ * Allow a vfs{g,u}id to be used as a k{g,u}id where we want to compare
+ * whether the mapped value is identical to value of a k{g,u}id.
+ */
+#define AS_KUIDT(val) (kuid_t){ __vfsuid_val(val) }
+#define AS_KGIDT(val) (kgid_t){ __vfsgid_val(val) }
+
+#ifdef CONFIG_MULTIUSER
+/**
+ * vfsgid_in_group_p() - check whether a vfsuid matches the caller's groups
+ * @vfsgid: the mnt gid to match
+ *
+ * This function can be used to determine whether @vfsuid matches any of the
+ * caller's groups.
+ *
+ * Return: 1 if vfsuid matches caller's groups, 0 if not.
+ */
+static inline int vfsgid_in_group_p(vfsgid_t vfsgid)
+{
+ return in_group_p(AS_KGIDT(vfsgid));
+}
+#else
+static inline int vfsgid_in_group_p(vfsgid_t vfsgid)
+{
+ return 1;
+}
+#endif
+
/**
* initial_idmapping - check whether this is the initial mapping
* @ns: idmapping to check
@@ -157,6 +273,43 @@ static inline kuid_t mapped_kuid_user(struct user_namespace *mnt_userns,
return make_kuid(fs_userns, uid);
}
+/**
+ * vfsuid_to_kuid - map a vfsuid into the filesystem idmapping
+ * @mnt_userns: the mount's idmapping
+ * @fs_userns: the filesystem's idmapping
+ * @vfsuid : vfsuid to be mapped
+ *
+ * Map @vfsuid into the filesystem idmapping. This function has to be used in
+ * order to e.g. write @vfsuid to inode->i_uid.
+ *
+ * Return: @vfsuid mapped into the filesystem idmapping
+ */
+static inline kuid_t vfsuid_to_kuid(struct user_namespace *mnt_userns,
+ struct user_namespace *fs_userns,
+ vfsuid_t vfsuid)
+{
+ return mapped_kuid_user(mnt_userns, fs_userns, AS_KUIDT(vfsuid));
+}
+
+/**
+ * vfsuid_has_mapping - check whether a vfsuid maps into the filesystem
+ * @mnt_userns: the mount's idmapping
+ * @fs_userns: the filesystem's idmapping
+ * @vfsuid: vfsuid to be mapped
+ *
+ * Check whether @vfsuid has a mapping in the filesystem idmapping. Use this
+ * function to check whether the filesystem idmapping has a mapping for
+ * @vfsuid.
+ *
+ * Return: true if @vfsuid has a mapping in the filesystem, false if not.
+ */
+static inline bool vfsuid_has_mapping(struct user_namespace *mnt_userns,
+ struct user_namespace *fs_userns,
+ vfsuid_t vfsuid)
+{
+ return uid_valid(vfsuid_to_kuid(mnt_userns, fs_userns, vfsuid));
+}
+
/**
* mapped_kgid_user - map a user kgid into a mnt_userns
* @mnt_userns: the mount's idmapping
@@ -193,6 +346,43 @@ static inline kgid_t mapped_kgid_user(struct user_namespace *mnt_userns,
return make_kgid(fs_userns, gid);
}
+/**
+ * vfsgid_to_kgid - map a vfsgid into the filesystem idmapping
+ * @mnt_userns: the mount's idmapping
+ * @fs_userns: the filesystem's idmapping
+ * @vfsgid : vfsgid to be mapped
+ *
+ * Map @vfsgid into the filesystem idmapping. This function has to be used in
+ * order to e.g. write @vfsgid to inode->i_gid.
+ *
+ * Return: @vfsgid mapped into the filesystem idmapping
+ */
+static inline kgid_t vfsgid_to_kgid(struct user_namespace *mnt_userns,
+ struct user_namespace *fs_userns,
+ vfsgid_t vfsgid)
+{
+ return mapped_kgid_user(mnt_userns, fs_userns, AS_KGIDT(vfsgid));
+}
+
+/**
+ * vfsgid_has_mapping - check whether a vfsgid maps into the filesystem
+ * @mnt_userns: the mount's idmapping
+ * @fs_userns: the filesystem's idmapping
+ * @vfsgid: vfsgid to be mapped
+ *
+ * Check whether @vfsgid has a mapping in the filesystem idmapping. Use this
+ * function to check whether the filesystem idmapping has a mapping for
+ * @vfsgid.
+ *
+ * Return: true if @vfsgid has a mapping in the filesystem, false if not.
+ */
+static inline bool vfsgid_has_mapping(struct user_namespace *mnt_userns,
+ struct user_namespace *fs_userns,
+ vfsgid_t vfsgid)
+{
+ return gid_valid(vfsgid_to_kgid(mnt_userns, fs_userns, vfsgid));
+}
+
/**
* mapped_fsuid - return caller's fsuid mapped up into a mnt_userns
* @mnt_userns: the mount's idmapping
--
2.34.1
