Base on the discussion in the following mail loop about checking
capability in sysfs write handler:
https://lkml.org/lkml/2018/9/13/978
Some sysfs write handler are checking the writer's capability by using
capable(). Base on CVE-2013-1959, those code should use file_ns_capable()
to check the opener's capability. Otherwise the capability checking logic
can be bypassed.
This patch adds hook to sysfs_ops that it allows different implementation
in object and attribute levels for checking file capable before
accessing sysfs interfaces.
The callback function in kobject sysfs_ops is the first implementation of
new hook. It casts attribute to kobj_attribute and calls the file
capability callback function in kobject attribute level.
Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael.j.wyso...@intel.com>
Cc: Chen Yu <yu.c.c...@intel.com>
Cc: Giovanni Gherdovich <ggherdov...@suse.cz>
Cc: Jann Horn <ja...@google.com>
Cc: Andy Lutomirski <l...@kernel.org>
Cc: Pavel Machek <pa...@ucw.cz>
Cc: Len Brown <len.br...@intel.com>
Cc: "Martin K. Petersen" <martin.peter...@oracle.com>
Cc: Randy Dunlap <rdun...@infradead.org>
Cc: Joe Perches <j...@perches.com>
Cc: Bart Van Assche <bvanass...@acm.org>
Signed-off-by: "Lee, Chun-Yi" <j...@suse.com>
---
fs/sysfs/file.c | 8 ++++++++
include/linux/kobject.h | 2 ++
include/linux/sysfs.h | 2 ++
lib/kobject.c | 26 ++++++++++++++++++++++++++
4 files changed, 38 insertions(+)
diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index bb71db63c99c..cf98957babd0 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -58,6 +58,10 @@ static int sysfs_kf_seq_show(struct seq_file *sf, void *v)
* if @ops->show() isn't implemented.
*/
if (ops->show) {
+ if (ops->show_file_capable &&
+ !ops->show_file_capable(of->file, of->kn->priv))
+ return -EPERM;
+
count = ops->show(kobj, of->kn->priv, buf);
if (count < 0)
return count;
@@ -136,6 +140,10 @@ static ssize_t sysfs_kf_write(struct kernfs_open_file *of,
char *buf,
if (!count)
return 0;
+ if (ops->store_file_capable &&
+ !ops->store_file_capable(of->file, of->kn->priv))
+ return -EPERM;
+
return ops->store(kobj, of->kn->priv, buf, count);
}
diff --git a/include/linux/kobject.h b/include/linux/kobject.h
index 1ab0d624fb36..f89fd692e812 100644
--- a/include/linux/kobject.h
+++ b/include/linux/kobject.h
@@ -166,6 +166,8 @@ struct kobj_attribute {
char *buf);
ssize_t (*store)(struct kobject *kobj, struct kobj_attribute *attr,
const char *buf, size_t count);
+ bool (*show_file_capable)(const struct file *);
+ bool (*store_file_capable)(const struct file *);
};
extern const struct sysfs_ops kobj_sysfs_ops;
diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index 786816cf4aa5..0b107795bee4 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -214,6 +214,8 @@ struct bin_attribute bin_attr_##_name =
__BIN_ATTR_RW(_name, _size)
struct sysfs_ops {
ssize_t (*show)(struct kobject *, struct attribute *, char *);
ssize_t (*store)(struct kobject *, struct attribute *, const char *,
size_t);
+ bool (*show_file_capable)(const struct file *, struct attribute *);
+ bool (*store_file_capable)(const struct file *, struct attribute *);
};
#ifdef CONFIG_SYSFS
diff --git a/lib/kobject.c b/lib/kobject.c
index b72e00fd7d09..81699b2b7f72 100644
--- a/lib/kobject.c
+++ b/lib/kobject.c
@@ -800,6 +800,18 @@ static ssize_t kobj_attr_show(struct kobject *kobj, struct
attribute *attr,
return ret;
}
+static bool kobj_attr_show_file_capable(const struct file *file,
+ struct attribute *attr)
+{
+ struct kobj_attribute *kattr;
+
+ kattr = container_of(attr, struct kobj_attribute, attr);
+ if (kattr->show_file_capable)
+ return kattr->show_file_capable(file);
+
+ return true;
+}
+
static ssize_t kobj_attr_store(struct kobject *kobj, struct attribute *attr,
const char *buf, size_t count)
{
@@ -812,9 +824,23 @@ static ssize_t kobj_attr_store(struct kobject *kobj,
struct attribute *attr,
return ret;
}
+static bool kobj_attr_store_file_capable(const struct file *file,
+ struct attribute *attr)
+{
+ struct kobj_attribute *kattr;
+
+ kattr = container_of(attr, struct kobj_attribute, attr);
+ if (kattr->store_file_capable)
+ return kattr->store_file_capable(file);
+
+ return true;
+}
+
const struct sysfs_ops kobj_sysfs_ops = {
.show = kobj_attr_show,
.store = kobj_attr_store,
+ .show_file_capable = kobj_attr_show_file_capable,
+ .store_file_capable = kobj_attr_store_file_capable,
};
EXPORT_SYMBOL_GPL(kobj_sysfs_ops);
--
2.13.6
