Merge tag 'fs.idmapped.vfsuid.v5.20' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux

Pull fs idmapping updates from Christian Brauner:
 "This introduces the new vfs{g,u}id_t types we agreed on. Similar to
  k{g,u}id_t the new types are just simple wrapper structs around
  regular {g,u}id_t types.

  They allow to establish a type safety boundary in the VFS for idmapped
  mounts preventing confusion betwen {g,u}ids mapped into an idmapped
  mount and {g,u}ids mapped into the caller's or the filesystem's
  idmapping.

  An initial set of helpers is introduced that allows to operate on
  vfs{g,u}id_t types. We will remove all references to non-type safe
  idmapped mounts helpers in the very near future. The patches do
  already exist.

  This converts the core attribute changing codepaths which become
  significantly easier to reason about because of this change.

  Just a few highlights here as the patches give detailed overviews of
  what is happening in the commit messages:

   - The kernel internal struct iattr contains type safe vfs{g,u}id_t
     values clearly communicating that these values have to take a given
     mount's idmapping into account.

   - The ownership values placed in struct iattr to change ownership are
     identical for idmapped and non-idmapped mounts going forward. This
     also allows to simplify stacking filesystems such as overlayfs that
     change attributes In other words, they always represent the values.

   - Instead of open coding checks for whether ownership changes have
     been requested and an actual update of the inode is required we now
     have small static inline wrappers that abstract this logic away
     removing a lot of code duplication from individual filesystems that
     all open-coded the same checks"

* tag 'fs.idmapped.vfsuid.v5.20' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux:
  mnt_idmapping: align kernel doc and parameter order
  mnt_idmapping: use new helpers in mapped_fs{g,u}id()
  fs: port HAS_UNMAPPED_ID() to vfs{g,u}id_t
  mnt_idmapping: return false when comparing two invalid ids
  attr: fix kernel doc
  attr: port attribute changes to new types
  security: pass down mount idmapping to setattr hook
  quota: port quota helpers mount ids
  fs: port to iattr ownership update helpers
  fs: introduce tiny iattr ownership update helpers
  fs: use mount types in iattr
  fs: add two type safe mapping helpers
  mnt_idmapping: add vfs{g,u}id_t

1 files changed, 247 insertions, 32 deletions

diff --git a/include/linux/mnt_idmapping.h b/include/linux/mnt_idmapping.h
index ee5a217de2a8..41dc80f8b67c 100644
--- a/include/linux/mnt_idmapping.h
+++ b/include/linux/mnt_idmapping.h
@@ -13,6 +13,129 @@ struct user_namespace;
  */
 extern struct user_namespace init_user_ns;
 
+typedef struct {
+	uid_t val;
+} vfsuid_t;
+
+typedef struct {
+	gid_t val;
+} vfsgid_t;
+
+static_assert(sizeof(vfsuid_t) == sizeof(kuid_t));
+static_assert(sizeof(vfsgid_t) == sizeof(kgid_t));
+static_assert(offsetof(vfsuid_t, val) == offsetof(kuid_t, val));
+static_assert(offsetof(vfsgid_t, val) == offsetof(kgid_t, val));
+
+#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;
+}
+
+static inline bool vfsuid_eq(vfsuid_t left, vfsuid_t right)
+{
+	return vfsuid_valid(left) && __vfsuid_val(left) == __vfsuid_val(right);
+}
+
+static inline bool vfsgid_eq(vfsgid_t left, vfsgid_t right)
+{
+	return vfsgid_valid(left) && __vfsgid_val(left) == __vfsgid_val(right);
+}
+
+/**
+ * vfsuid_eq_kuid - check whether kuid and vfsuid have the same value
+ * @vfsuid: the vfsuid to compare
+ * @kuid: the kuid to compare
+ *
+ * Check whether @vfsuid and @kuid have the same values.
+ *
+ * Return: true if @vfsuid and @kuid have the same value, false if not.
+ * Comparison between two invalid uids returns false.
+ */
+static inline bool vfsuid_eq_kuid(vfsuid_t vfsuid, kuid_t kuid)
+{
+	return vfsuid_valid(vfsuid) && __vfsuid_val(vfsuid) == __kuid_val(kuid);
+}
+
+/**
+ * vfsgid_eq_kgid - check whether kgid and vfsgid have the same value
+ * @vfsgid: the vfsgid to compare
+ * @kgid: the kgid to compare
+ *
+ * Check whether @vfsgid and @kgid have the same values.
+ *
+ * Return: true if @vfsgid and @kgid have the same value, false if not.
+ * Comparison between two invalid gids returns false.
+ */
+static inline bool vfsgid_eq_kgid(vfsgid_t vfsgid, kgid_t kgid)
+{
+	return vfsgid_valid(vfsgid) && __vfsgid_val(vfsgid) == __kgid_val(kgid);
+}
+
+/*
+ * 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
@@ -48,7 +171,7 @@ static inline bool no_idmapping(const struct user_namespace *mnt_userns,
 }
 
 /**
- * mapped_kuid_fs - map a filesystem kuid into a mnt_userns
+ * make_vfsuid - 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
@@ -67,25 +190,33 @@ static inline bool no_idmapping(const struct user_namespace *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)
+
+static inline vfsuid_t make_vfsuid(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;
+		return VFSUIDT_INIT(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);
+		return INVALID_VFSUID;
+	return VFSUIDT_INIT(make_kuid(mnt_userns, uid));
+}
+
+static inline kuid_t mapped_kuid_fs(struct user_namespace *mnt_userns,
+				    struct user_namespace *fs_userns,
+				    kuid_t kuid)
+{
+	return AS_KUIDT(make_vfsuid(mnt_userns, fs_userns, kuid));
 }
 
 /**
- * mapped_kgid_fs - map a filesystem kgid into a mnt_userns
+ * make_vfsgid - 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
@@ -104,21 +235,56 @@ static inline kuid_t mapped_kuid_fs(struct user_namespace *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)
+
+static inline vfsgid_t make_vfsgid(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;
+		return VFSGIDT_INIT(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);
+		return INVALID_VFSGID;
+	return VFSGIDT_INIT(make_kgid(mnt_userns, gid));
+}
+
+static inline kgid_t mapped_kgid_fs(struct user_namespace *mnt_userns,
+				    struct user_namespace *fs_userns,
+				    kgid_t kgid)
+{
+	return AS_KGIDT(make_vfsgid(mnt_userns, fs_userns, kgid));
+}
+
+/**
+ * from_vfsuid - 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 from_vfsuid(struct user_namespace *mnt_userns,
+				 struct user_namespace *fs_userns,
+				 vfsuid_t vfsuid)
+{
+	uid_t uid;
+
+	if (no_idmapping(mnt_userns, fs_userns))
+		return AS_KUIDT(vfsuid);
+	uid = from_kuid(mnt_userns, AS_KUIDT(vfsuid));
+	if (uid == (uid_t)-1)
+		return INVALID_UID;
+	if (initial_idmapping(fs_userns))
+		return KUIDT_INIT(uid);
+	return make_kuid(fs_userns, uid);
 }
 
 /**
@@ -145,16 +311,53 @@ static inline kuid_t mapped_kuid_user(struct user_namespace *mnt_userns,
 				      struct user_namespace *fs_userns,
 				      kuid_t kuid)
 {
-	uid_t uid;
+	return from_vfsuid(mnt_userns, fs_userns, VFSUIDT_INIT(kuid));
+}
+
+/**
+ * vfsuid_has_fsmapping - 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_fsmapping(struct user_namespace *mnt_userns,
+					struct user_namespace *fs_userns,
+					vfsuid_t vfsuid)
+{
+	return uid_valid(from_vfsuid(mnt_userns, fs_userns, vfsuid));
+}
+
+/**
+ * from_vfsgid - 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 from_vfsgid(struct user_namespace *mnt_userns,
+				 struct user_namespace *fs_userns,
+				 vfsgid_t vfsgid)
+{
+	gid_t gid;
 
 	if (no_idmapping(mnt_userns, fs_userns))
-		return kuid;
-	uid = from_kuid(mnt_userns, kuid);
-	if (uid == (uid_t)-1)
-		return INVALID_UID;
+		return AS_KGIDT(vfsgid);
+	gid = from_kgid(mnt_userns, AS_KGIDT(vfsgid));
+	if (gid == (gid_t)-1)
+		return INVALID_GID;
 	if (initial_idmapping(fs_userns))
-		return KUIDT_INIT(uid);
-	return make_kuid(fs_userns, uid);
+		return KGIDT_INIT(gid);
+	return make_kgid(fs_userns, gid);
 }
 
 /**
@@ -181,16 +384,26 @@ static inline kgid_t mapped_kgid_user(struct user_namespace *mnt_userns,
 				      struct user_namespace *fs_userns,
 				      kgid_t kgid)
 {
-	gid_t gid;
+	return from_vfsgid(mnt_userns, fs_userns, VFSGIDT_INIT(kgid));
+}
 
-	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);
+/**
+ * vfsgid_has_fsmapping - 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_fsmapping(struct user_namespace *mnt_userns,
+					struct user_namespace *fs_userns,
+					vfsgid_t vfsgid)
+{
+	return gid_valid(from_vfsgid(mnt_userns, fs_userns, vfsgid));
 }
 
 /**
@@ -209,7 +422,8 @@ static inline kgid_t mapped_kgid_user(struct user_namespace *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());
+	return from_vfsuid(mnt_userns, fs_userns,
+			   VFSUIDT_INIT(current_fsuid()));
 }
 
 /**
@@ -228,7 +442,8 @@ static inline kuid_t mapped_fsuid(struct user_namespace *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());
+	return from_vfsgid(mnt_userns, fs_userns,
+			   VFSGIDT_INIT(current_fsgid()));
 }
 
 #endif /* _LINUX_MNT_IDMAPPING_H */