summaryrefslogtreecommitdiff
path: root/include/linux/mnt_idmapping.h
diff options
context:
space:
mode:
Diffstat (limited to 'include/linux/mnt_idmapping.h')
-rw-r--r--include/linux/mnt_idmapping.h234
1 files changed, 234 insertions, 0 deletions
diff --git a/include/linux/mnt_idmapping.h b/include/linux/mnt_idmapping.h
new file mode 100644
index 000000000000..ee5a217de2a8
--- /dev/null
+++ b/include/linux/mnt_idmapping.h
@@ -0,0 +1,234 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_MNT_IDMAPPING_H
+#define _LINUX_MNT_IDMAPPING_H
+
+#include <linux/types.h>
+#include <linux/uidgid.h>
+
+struct user_namespace;
+/*
+ * Carries the initial idmapping of 0:0:4294967295 which is an identity
+ * mapping. This means that {g,u}id 0 is mapped to {g,u}id 0, {g,u}id 1 is
+ * mapped to {g,u}id 1, [...], {g,u}id 1000 to {g,u}id 1000, [...].
+ */
+extern struct user_namespace init_user_ns;
+
+/**
+ * initial_idmapping - check whether this is the initial mapping
+ * @ns: idmapping to check
+ *
+ * Check whether this is the initial mapping, mapping 0 to 0, 1 to 1,
+ * [...], 1000 to 1000 [...].
+ *
+ * Return: true if this is the initial mapping, false if not.
+ */
+static inline bool initial_idmapping(const struct user_namespace *ns)
+{
+ return ns == &init_user_ns;
+}
+
+/**
+ * no_idmapping - check whether we can skip remapping a kuid/gid
+ * @mnt_userns: the mount's idmapping
+ * @fs_userns: the filesystem's idmapping
+ *
+ * This function can be used to check whether a remapping between two
+ * idmappings is required.
+ * An idmapped mount is a mount that has an idmapping attached to it that
+ * is different from the filsystem's idmapping and the initial idmapping.
+ * If the initial mapping is used or the idmapping of the mount and the
+ * filesystem are identical no remapping is required.
+ *
+ * Return: true if remapping can be skipped, false if not.
+ */
+static inline bool no_idmapping(const struct user_namespace *mnt_userns,
+ const struct user_namespace *fs_userns)
+{
+ return initial_idmapping(mnt_userns) || mnt_userns == fs_userns;
+}
+
+/**
+ * mapped_kuid_fs - map a filesystem kuid into a mnt_userns
+ * @mnt_userns: the mount's idmapping
+ * @fs_userns: the filesystem's idmapping
+ * @kuid : kuid to be mapped
+ *
+ * Take a @kuid and remap it from @fs_userns into @mnt_userns. Use this
+ * function when preparing a @kuid to be reported to userspace.
+ *
+ * If no_idmapping() determines that this is not an idmapped mount we can
+ * simply return @kuid unchanged.
+ * If initial_idmapping() tells us that the filesystem is not mounted with an
+ * idmapping we know the value of @kuid won't change when calling
+ * from_kuid() so we can simply retrieve the value via __kuid_val()
+ * directly.
+ *
+ * Return: @kuid mapped according to @mnt_userns.
+ * If @kuid has no mapping in either @mnt_userns or @fs_userns INVALID_UID is
+ * returned.
+ */
+static inline kuid_t mapped_kuid_fs(struct user_namespace *mnt_userns,
+ struct user_namespace *fs_userns,
+ kuid_t kuid)
+{
+ uid_t uid;
+
+ if (no_idmapping(mnt_userns, fs_userns))
+ return kuid;
+ if (initial_idmapping(fs_userns))
+ uid = __kuid_val(kuid);
+ else
+ uid = from_kuid(fs_userns, kuid);
+ if (uid == (uid_t)-1)
+ return INVALID_UID;
+ return make_kuid(mnt_userns, uid);
+}
+
+/**
+ * mapped_kgid_fs - map a filesystem kgid into a mnt_userns
+ * @mnt_userns: the mount's idmapping
+ * @fs_userns: the filesystem's idmapping
+ * @kgid : kgid to be mapped
+ *
+ * Take a @kgid and remap it from @fs_userns into @mnt_userns. Use this
+ * function when preparing a @kgid to be reported to userspace.
+ *
+ * If no_idmapping() determines that this is not an idmapped mount we can
+ * simply return @kgid unchanged.
+ * If initial_idmapping() tells us that the filesystem is not mounted with an
+ * idmapping we know the value of @kgid won't change when calling
+ * from_kgid() so we can simply retrieve the value via __kgid_val()
+ * directly.
+ *
+ * Return: @kgid mapped according to @mnt_userns.
+ * If @kgid has no mapping in either @mnt_userns or @fs_userns INVALID_GID is
+ * returned.
+ */
+static inline kgid_t mapped_kgid_fs(struct user_namespace *mnt_userns,
+ struct user_namespace *fs_userns,
+ kgid_t kgid)
+{
+ gid_t gid;
+
+ if (no_idmapping(mnt_userns, fs_userns))
+ return kgid;
+ if (initial_idmapping(fs_userns))
+ gid = __kgid_val(kgid);
+ else
+ gid = from_kgid(fs_userns, kgid);
+ if (gid == (gid_t)-1)
+ return INVALID_GID;
+ return make_kgid(mnt_userns, gid);
+}
+
+/**
+ * mapped_kuid_user - map a user kuid into a mnt_userns
+ * @mnt_userns: the mount's idmapping
+ * @fs_userns: the filesystem's idmapping
+ * @kuid : kuid to be mapped
+ *
+ * Use the idmapping of @mnt_userns to remap a @kuid into @fs_userns. Use this
+ * function when preparing a @kuid to be written to disk or inode.
+ *
+ * If no_idmapping() determines that this is not an idmapped mount we can
+ * simply return @kuid unchanged.
+ * If initial_idmapping() tells us that the filesystem is not mounted with an
+ * idmapping we know the value of @kuid won't change when calling
+ * make_kuid() so we can simply retrieve the value via KUIDT_INIT()
+ * directly.
+ *
+ * Return: @kuid mapped according to @mnt_userns.
+ * If @kuid has no mapping in either @mnt_userns or @fs_userns INVALID_UID is
+ * returned.
+ */
+static inline kuid_t mapped_kuid_user(struct user_namespace *mnt_userns,
+ struct user_namespace *fs_userns,
+ kuid_t kuid)
+{
+ uid_t uid;
+
+ if (no_idmapping(mnt_userns, fs_userns))
+ return kuid;
+ uid = from_kuid(mnt_userns, kuid);
+ if (uid == (uid_t)-1)
+ return INVALID_UID;
+ if (initial_idmapping(fs_userns))
+ return KUIDT_INIT(uid);
+ return make_kuid(fs_userns, uid);
+}
+
+/**
+ * mapped_kgid_user - map a user kgid into a mnt_userns
+ * @mnt_userns: the mount's idmapping
+ * @fs_userns: the filesystem's idmapping
+ * @kgid : kgid to be mapped
+ *
+ * Use the idmapping of @mnt_userns to remap a @kgid into @fs_userns. Use this
+ * function when preparing a @kgid to be written to disk or inode.
+ *
+ * If no_idmapping() determines that this is not an idmapped mount we can
+ * simply return @kgid unchanged.
+ * If initial_idmapping() tells us that the filesystem is not mounted with an
+ * idmapping we know the value of @kgid won't change when calling
+ * make_kgid() so we can simply retrieve the value via KGIDT_INIT()
+ * directly.
+ *
+ * Return: @kgid mapped according to @mnt_userns.
+ * If @kgid has no mapping in either @mnt_userns or @fs_userns INVALID_GID is
+ * returned.
+ */
+static inline kgid_t mapped_kgid_user(struct user_namespace *mnt_userns,
+ struct user_namespace *fs_userns,
+ kgid_t kgid)
+{
+ gid_t gid;
+
+ if (no_idmapping(mnt_userns, fs_userns))
+ return kgid;
+ gid = from_kgid(mnt_userns, kgid);
+ if (gid == (gid_t)-1)
+ return INVALID_GID;
+ if (initial_idmapping(fs_userns))
+ return KGIDT_INIT(gid);
+ return make_kgid(fs_userns, gid);
+}
+
+/**
+ * mapped_fsuid - return caller's fsuid mapped up into a mnt_userns
+ * @mnt_userns: the mount's idmapping
+ * @fs_userns: the filesystem's idmapping
+ *
+ * Use this helper to initialize a new vfs or filesystem object based on
+ * the caller's fsuid. A common example is initializing the i_uid field of
+ * a newly allocated inode triggered by a creation event such as mkdir or
+ * O_CREAT. Other examples include the allocation of quotas for a specific
+ * user.
+ *
+ * Return: the caller's current fsuid mapped up according to @mnt_userns.
+ */
+static inline kuid_t mapped_fsuid(struct user_namespace *mnt_userns,
+ struct user_namespace *fs_userns)
+{
+ return mapped_kuid_user(mnt_userns, fs_userns, current_fsuid());
+}
+
+/**
+ * mapped_fsgid - return caller's fsgid mapped up into a mnt_userns
+ * @mnt_userns: the mount's idmapping
+ * @fs_userns: the filesystem's idmapping
+ *
+ * Use this helper to initialize a new vfs or filesystem object based on
+ * the caller's fsgid. A common example is initializing the i_gid field of
+ * a newly allocated inode triggered by a creation event such as mkdir or
+ * O_CREAT. Other examples include the allocation of quotas for a specific
+ * user.
+ *
+ * Return: the caller's current fsgid mapped up according to @mnt_userns.
+ */
+static inline kgid_t mapped_fsgid(struct user_namespace *mnt_userns,
+ struct user_namespace *fs_userns)
+{
+ return mapped_kgid_user(mnt_userns, fs_userns, current_fsgid());
+}
+
+#endif /* _LINUX_MNT_IDMAPPING_H */