[PATCH v5 14/30] internal: add may_write_xattr()
From: Christian Brauner <brauner@kernel.org>
Date: 2022-10-18 11:59:16
Also in:
linux-fsdevel
Subsystem:
filesystems (vfs and infrastructure), the rest · Maintainers:
Alexander Viro, Christian Brauner, Linus Torvalds
Split out the generic checks whether an inode allows writing xattrs. Since
security.* and system.* xattrs don't have any restrictions and we're going
to split out posix acls into a dedicated api we will use this helper to
check whether we can write posix acls.
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
---
Notes:
/* v2 */
patch not present
/* v3 */
patch not present
/* v4 */
Christoph Hellwig [off-list ref]:
- Split out checks whether an inode can have xattrs written to into a helper.
/* v5 */
unchanged
fs/internal.h | 1 +
fs/xattr.c | 43 ++++++++++++++++++++++++++++++-------------
2 files changed, 31 insertions(+), 13 deletions(-)
diff --git a/fs/internal.h b/fs/internal.h
index 6f0386b34fae..de43795ab7cd 100644
--- a/fs/internal.h
+++ b/fs/internal.h@@ -234,3 +234,4 @@ int do_setxattr(struct user_namespace *mnt_userns, struct dentry *dentry, struct xattr_ctx *ctx); ssize_t __kernel_write_iter(struct file *file, struct iov_iter *from, loff_t *pos); +int may_write_xattr(struct user_namespace *mnt_userns, struct inode *inode);
diff --git a/fs/xattr.c b/fs/xattr.c
index 61107b6bbed2..31b5ac65ca34 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c@@ -80,6 +80,31 @@ xattr_resolve_name(struct inode *inode, const char **name) return ERR_PTR(-EOPNOTSUPP); } +/** + * may_write_xattr - check whether inode allows writing xattr + * @mnt_userns: User namespace of the mount the inode was found from + * @inode: the inode on which to set an xattr + * + * Check whether the inode allows writing xattrs. Specifically, we can never + * set or remove an extended attribute on a read-only filesystem or on an + * immutable / append-only inode. + * + * We also need to ensure that the inode has a mapping in the mount to + * not risk writing back invalid i_{g,u}id values. + * + * Return: On success zero is returned. On error a negative errno is returned. + */ +int may_write_xattr(struct user_namespace *mnt_userns, struct inode *inode) +{ + if (IS_IMMUTABLE(inode)) + return -EPERM; + if (IS_APPEND(inode)) + return -EPERM; + if (HAS_UNMAPPED_ID(mnt_userns, inode)) + return -EPERM; + return 0; +} + /* * Check permissions for extended attribute access. This is a bit complicated * because different namespaces have very different rules.
@@ -88,20 +113,12 @@ static int xattr_permission(struct user_namespace *mnt_userns, struct inode *inode, const char *name, int mask) { - /* - * We can never set or remove an extended attribute on a read-only - * filesystem or on an immutable / append-only inode. - */ if (mask & MAY_WRITE) { - if (IS_IMMUTABLE(inode) || IS_APPEND(inode)) - return -EPERM; - /* - * Updating an xattr will likely cause i_uid and i_gid - * to be writen back improperly if their true value is - * unknown to the vfs. - */ - if (HAS_UNMAPPED_ID(mnt_userns, inode)) - return -EPERM; + int ret; + + ret = may_write_xattr(mnt_userns, inode); + if (ret) + return ret; } /*
--
2.34.1