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@xxxxxxxxxx>
---
Notes:
/* v2 */
patch not present
/* v3 */
patch not present
/* v4 */
Christoph Hellwig <hch@xxxxxx>:
- 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
