Revert "(namespace) Revert "UBUNTU: SAUCE: fs: Update posix_acl support to...

Revert "(namespace) Revert "UBUNTU: SAUCE: fs: Update posix_acl support to handle user namespace mounts""

BugLink: https://bugs.launchpad.net/bugs/1644165

This reverts commit aad49181.

The kernel fix for bug #1634964 breaks LXD userspace, in particular the
following commits:

ac7f3f73 (namespace) vfs: Don't modify inodes with a uid or gid unknown to the vfs
ca52383a (namespace) vfs: Don't create inodes with a uid or gid unknown to the vfs

LXD 2.0.6 will include changes to support these kernel changes, but it isn't
available yet on xenial, so for now we just revert these commits.
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

fs/posix_acl.c

@@ -626,59 +626,77 @@ EXPORT_SYMBOL(posix_acl_update_mode);
 /*
  * Fix up the uids and gids in posix acl extended attributes in place.
  */
-static void posix_acl_fix_xattr_userns(
+static int posix_acl_fix_xattr_userns(
 	struct user_namespace *to, struct user_namespace *from,
 	void *value, size_t size)
 {
 	posix_acl_xattr_header *header = (posix_acl_xattr_header *)value;
 	posix_acl_xattr_entry *entry = (posix_acl_xattr_entry *)(header+1), *end;
 	int count;
-	kuid_t uid;
-	kgid_t gid;
+	kuid_t kuid;
+	uid_t uid;
+	kgid_t kgid;
+	gid_t gid;
 
 	if (!value)
-		return;
+		return 0;
 	if (size < sizeof(posix_acl_xattr_header))
-		return;
+		return 0;
 	if (header->a_version != cpu_to_le32(POSIX_ACL_XATTR_VERSION))
-		return;
+		return 0;
 
 	count = posix_acl_xattr_count(size);
 	if (count < 0)
-		return;
+		return 0;
 	if (count == 0)
-		return;
+		return 0;
 
 	for (end = entry + count; entry != end; entry++) {
 		switch(le16_to_cpu(entry->e_tag)) {
 		case ACL_USER:
-			uid = make_kuid(from, le32_to_cpu(entry->e_id));
-			entry->e_id = cpu_to_le32(from_kuid(to, uid));
+			kuid = make_kuid(from, le32_to_cpu(entry->e_id));
+			if (!uid_valid(kuid))
+				return -EOVERFLOW;
+			uid = from_kuid(to, kuid);
+			if (uid == (uid_t)-1)
+				return -EOVERFLOW;
+			entry->e_id = cpu_to_le32(uid);
 			break;
 		case ACL_GROUP:
-			gid = make_kgid(from, le32_to_cpu(entry->e_id));
-			entry->e_id = cpu_to_le32(from_kgid(to, gid));
+			kgid = make_kgid(from, le32_to_cpu(entry->e_id));
+			if (!gid_valid(kgid))
+				return -EOVERFLOW;
+			gid = from_kgid(to, kgid);
+			if (gid == (gid_t)-1)
+				return -EOVERFLOW;
+			entry->e_id = cpu_to_le32(gid);
 			break;
 		default:
 			break;
 		}
 	}
+
+	return 0;
 }
 
-void posix_acl_fix_xattr_from_user(void *value, size_t size)
+int
+posix_acl_fix_xattr_from_user(struct user_namespace *target_ns, void *value,
+			      size_t size)
 {
-	struct user_namespace *user_ns = current_user_ns();
-	if (user_ns == &init_user_ns)
-		return;
-	posix_acl_fix_xattr_userns(&init_user_ns, user_ns, value, size);
+	struct user_namespace *source_ns = current_user_ns();
+	if (source_ns == target_ns)
+		return 0;
+	return posix_acl_fix_xattr_userns(target_ns, source_ns, value, size);
 }
 
-void posix_acl_fix_xattr_to_user(void *value, size_t size)
+int
+posix_acl_fix_xattr_to_user(struct user_namespace *source_ns, void *value,
+			    size_t size)
 {
-	struct user_namespace *user_ns = current_user_ns();
-	if (user_ns == &init_user_ns)
-		return;
-	posix_acl_fix_xattr_userns(user_ns, &init_user_ns, value, size);
+	struct user_namespace *target_ns = current_user_ns();
+	if (target_ns == source_ns)
+		return 0;
+	return posix_acl_fix_xattr_userns(target_ns, source_ns, value, size);
 }
 
 /*
@@ -813,7 +831,7 @@ posix_acl_xattr_get(const struct xattr_handler *handler,
 	if (acl == NULL)
 		return -ENODATA;
 
-	error = posix_acl_to_xattr(&init_user_ns, acl, value, size);
+	error = posix_acl_to_xattr(dentry->d_sb->s_user_ns, acl, value, size);
 	posix_acl_release(acl);
 
 	return error;
@@ -854,7 +872,8 @@ posix_acl_xattr_set(const struct xattr_handler *handler,
 		return -EINVAL;
 
 	if (value) {
-		acl = posix_acl_from_xattr(&init_user_ns, value, size);
+		acl = posix_acl_from_xattr(dentry->d_sb->s_user_ns, value,
+					   size);
 		if (IS_ERR(acl))
 			return PTR_ERR(acl);
 	}

fs/xattr.c

@@ -352,8 +352,12 @@ setxattr(struct dentry *d, const char __user *name, const void __user *value,
 			goto out;
 		}
 		if ((strcmp(kname, XATTR_NAME_POSIX_ACL_ACCESS) == 0) ||
-		    (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0))
-			posix_acl_fix_xattr_from_user(kvalue, size);
+		    (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0)) {
+			error = posix_acl_fix_xattr_from_user(d->d_sb->s_user_ns,
+							      kvalue, size);
+			if (error)
+				goto out;
+		}
 	}
 
 	error = vfs_setxattr(d, kname, kvalue, size, flags);
@@ -453,9 +457,14 @@ getxattr(struct dentry *d, const char __user *name, void __user *value,
 	error = vfs_getxattr(d, kname, kvalue, size);
 	if (error > 0) {
 		if ((strcmp(kname, XATTR_NAME_POSIX_ACL_ACCESS) == 0) ||
-		    (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0))
-			posix_acl_fix_xattr_to_user(kvalue, size);
-		if (size && copy_to_user(value, kvalue, error))
+		    (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0)) {
+			int ret;
+			ret = posix_acl_fix_xattr_to_user(d->d_sb->s_user_ns,
+							  kvalue, size);
+			if (ret)
+				error = ret;
+		}
+		if (error > 0 && size && copy_to_user(value, kvalue, error))
 			error = -EFAULT;
 	} else if (error == -ERANGE && size >= XATTR_SIZE_MAX) {
 		/* The file system tried to returned a value bigger

include/linux/posix_acl_xattr.h

@@ -53,14 +53,23 @@ posix_acl_xattr_count(size_t size)
 }
 
 #ifdef CONFIG_FS_POSIX_ACL
-void posix_acl_fix_xattr_from_user(void *value, size_t size);
-void posix_acl_fix_xattr_to_user(void *value, size_t size);
+int posix_acl_fix_xattr_from_user(struct user_namespace *target_ns,
+				  void *value, size_t size);
+int posix_acl_fix_xattr_to_user(struct user_namespace *source_ns, void *value,
+				size_t size);
 #else
-static inline void posix_acl_fix_xattr_from_user(void *value, size_t size)
+static inline int
+posix_acl_fix_xattr_from_user(struct user_namespace *target_ns, void *value,
+			      size_t size)
 {
+	return 0;
 }
-static inline void posix_acl_fix_xattr_to_user(void *value, size_t size)
+
+static inline int
+posix_acl_fix_xattr_to_user(struct user_namespace *source_ns, void *value,
+			    size_t size)
 {
+	return 0;
 }
 #endif