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Subject[PATCH v5 2/9] sysfs: add sysfs_link_change_owner()
Date
Add a helper to change the owner of a sysfs link.
This function will be used to correctly account for kobject ownership
changes, e.g. when moving network devices between network namespaces.

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
/* v2 */
- Greg Kroah-Hartman <gregkh@linuxfoundation.org>:
- Add comment how ownership of sysfs object is changed.

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

/* v4 */
- Christian Brauner <christian.brauner@ubuntu.com>:
- Add more documentation.

/* v5 */
unchanged
---
fs/sysfs/file.c | 41 +++++++++++++++++++++++++++++++++++++++++
include/linux/sysfs.h | 10 ++++++++++
2 files changed, 51 insertions(+)

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index 4ca936ca3ba4..332cd69b378c 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -570,6 +570,47 @@ static int internal_change_owner(struct kernfs_node *kn, kuid_t kuid,
return kernfs_setattr(kn, &newattrs);
}

+/**
+ * sysfs_link_change_owner - change owner of a sysfs file.
+ * @kobj: object of the kernfs_node the symlink is located in.
+ * @targ: object of the kernfs_node the symlink points to.
+ * @name: name of the link.
+ * @kuid: new owner's kuid
+ * @kgid: new owner's kgid
+ *
+ * This function looks up the sysfs symlink entry @name under @kobj and changes
+ * the ownership to @kuid/@kgid. The symlink is looked up in the namespace of
+ * @targ.
+ *
+ * Returns 0 on success or error code on failure.
+ */
+int sysfs_link_change_owner(struct kobject *kobj, struct kobject *targ,
+ const char *name, kuid_t kuid, kgid_t kgid)
+{
+ struct kernfs_node *kn = NULL;
+ int error;
+
+ if (!name || !kobj->state_in_sysfs || !targ->state_in_sysfs)
+ return -EINVAL;
+
+ error = -ENOENT;
+ kn = kernfs_find_and_get_ns(kobj->sd, name, targ->sd->ns);
+ if (!kn)
+ goto out;
+
+ error = -EINVAL;
+ if (kernfs_type(kn) != KERNFS_LINK)
+ goto out;
+ if (kn->symlink.target_kn->priv != targ)
+ goto out;
+
+ error = internal_change_owner(kn, kuid, kgid);
+
+out:
+ kernfs_put(kn);
+ return error;
+}
+
/**
* sysfs_file_change_owner - change owner of a sysfs file.
* @kobj: object.
diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index a7884024a911..7e15ebfd750e 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -312,6 +312,8 @@ static inline void sysfs_enable_ns(struct kernfs_node *kn)

int sysfs_file_change_owner(struct kobject *kobj, const char *name, kuid_t kuid,
kgid_t kgid);
+int sysfs_link_change_owner(struct kobject *kobj, struct kobject *targ,
+ const char *name, kuid_t kuid, kgid_t kgid);

#else /* CONFIG_SYSFS */

@@ -532,6 +534,14 @@ static inline int sysfs_file_change_owner(struct kobject *kobj,
return 0;
}

+static inline int sysfs_link_change_owner(struct kobject *kobj,
+ struct kobject *targ,
+ 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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