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Subject[PATCH v7 1/9] sysfs: add sysfs_file_change_owner()
Date
Add helpers to change the owner of a sysfs files.
This function will be used to correctly account for kobject ownership
changes, e.g. when moving network devices between network namespaces.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
/* v2 */
- Greg Kroah-Hartman <gregkh@linuxfoundation.org>:
- Better naming for sysfs_file_change_owner() to reflect the fact that it
can be used to change the owner of the kobject itself by passing NULL as
argument.
- Christian Brauner <christian.brauner@ubuntu.com>:
- Split sysfs_file_change_owner() into two helpers sysfs_change_owner() and
sysfs_change_owner_by_name(). The former changes the owner of the kobject
itself, the latter the owner of the kobject looked up via the name
argument.

/* v3 */
- Greg Kroah-Hartman <gregkh@linuxfoundation.org>:
- Add explicit uid/gid parameters.

/* v4 */
- Greg Kroah-Hartman <gregkh@linuxfoundation.org>:
- Remove the second helper which changes the ownership of the kobject itself
and do it in-place instead later on in the series. A separate helper is
not needed for that.
- Christian Brauner <christian.brauner@ubuntu.com>:
- Add more documentation.

/* v5 */
unchanged

/* v6 */
- Christian Brauner <christian.brauner@ubuntu.com>:
- Fix commit message which still referenced the old name of the helper.

/* v7 */
unchanged
---
fs/sysfs/file.c | 47 +++++++++++++++++++++++++++++++++++++++++++
include/linux/sysfs.h | 10 +++++++++
2 files changed, 57 insertions(+)

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index 130fc6fbcc03..4ca936ca3ba4 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -558,3 +558,50 @@ void sysfs_remove_bin_file(struct kobject *kobj,
kernfs_remove_by_name(kobj->sd, attr->attr.name);
}
EXPORT_SYMBOL_GPL(sysfs_remove_bin_file);
+
+static int internal_change_owner(struct kernfs_node *kn, kuid_t kuid,
+ kgid_t kgid)
+{
+ struct iattr newattrs = {
+ .ia_valid = ATTR_UID | ATTR_GID,
+ .ia_uid = kuid,
+ .ia_gid = kgid,
+ };
+ return kernfs_setattr(kn, &newattrs);
+}
+
+/**
+ * sysfs_file_change_owner - change owner of a sysfs file.
+ * @kobj: object.
+ * @name: name of the file to change.
+ * @kuid: new owner's kuid
+ * @kgid: new owner's kgid
+ *
+ * This function looks up the sysfs entry @name under @kobj and changes the
+ * ownership to @kuid/@kgid.
+ *
+ * Returns 0 on success or error code on failure.
+ */
+int sysfs_file_change_owner(struct kobject *kobj, const char *name, kuid_t kuid,
+ kgid_t kgid)
+{
+ struct kernfs_node *kn;
+ int error;
+
+ if (!name)
+ return -EINVAL;
+
+ if (!kobj->state_in_sysfs)
+ return -EINVAL;
+
+ kn = kernfs_find_and_get(kobj->sd, name);
+ if (!kn)
+ return -ENOENT;
+
+ error = internal_change_owner(kn, kuid, kgid);
+
+ kernfs_put(kn);
+
+ return error;
+}
+EXPORT_SYMBOL_GPL(sysfs_file_change_owner);
diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index fa7ee503fb76..a7884024a911 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -310,6 +310,9 @@ static inline void sysfs_enable_ns(struct kernfs_node *kn)
return kernfs_enable_ns(kn);
}

+int sysfs_file_change_owner(struct kobject *kobj, const char *name, kuid_t kuid,
+ kgid_t kgid);
+
#else /* CONFIG_SYSFS */

static inline int sysfs_create_dir_ns(struct kobject *kobj, const void *ns)
@@ -522,6 +525,13 @@ static inline void sysfs_enable_ns(struct kernfs_node *kn)
{
}

+static inline int sysfs_file_change_owner(struct kobject *kobj,
+ const char *name, kuid_t kuid,
+ kgid_t kgid)
+{
+ return 0;
+}
+
#endif /* CONFIG_SYSFS */

static inline int __must_check sysfs_create_file(struct kobject *kobj,
--
2.25.1
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