nilfs2: fix CFI failure when accessing /sys/fs/nilfs2/features/*

When accessing one of the files under /sys/fs/nilfs2/features when
CONFIG_CFI_CLANG is enabled, there is a CFI violation:

  CFI failure at kobj_attr_show+0x59/0x80 (target: nilfs_feature_revision_show+0x0/0x30; expected type: 0xfc392c4d)
  ...
  Call Trace:
   <TASK>
   sysfs_kf_seq_show+0x2a6/0x390
   ? __cfi_kobj_attr_show+0x10/0x10
   kernfs_seq_show+0x104/0x15b
   seq_read_iter+0x580/0xe2b
  ...

When the kobject of the kset for /sys/fs/nilfs2 is initialized, its ktype
is set to kset_ktype, which has a ->sysfs_ops of kobj_sysfs_ops.  When
nilfs_feature_attr_group is added to that kobject via
sysfs_create_group(), the kernfs_ops of each files is sysfs_file_kfops_rw,
which will call sysfs_kf_seq_show() when ->seq_show() is called. 
sysfs_kf_seq_show() in turn calls kobj_attr_show() through
->sysfs_ops->show().  kobj_attr_show() casts the provided attribute out to
a 'struct kobj_attribute' via container_of() and calls ->show(), resulting
in the CFI violation since neither nilfs_feature_revision_show() nor
nilfs_feature_README_show() match the prototype of ->show() in 'struct
kobj_attribute'.

Resolve the CFI violation by adjusting the second parameter in
nilfs_feature_{revision,README}_show() from 'struct attribute' to 'struct
kobj_attribute' to match the expected prototype.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: aebe17f ("nilfs2: add /sys/fs/nilfs2/features group")
Signed-off-by: Nathan Chancellor <[email protected]>
Signed-off-by: Ryusuke Konishi <[email protected]>
Reported-by: kernel test robot <[email protected]>
Closes: https://lore.kernel.org/oe-lkp/[email protected]/
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: nathanchance

fs/nilfs2/sysfs.c

@@ -1075,7 +1075,7 @@ void nilfs_sysfs_delete_device_group(struct the_nilfs *nilfs)
  ************************************************************************/
 
 static ssize_t nilfs_feature_revision_show(struct kobject *kobj,
-					    struct attribute *attr, char *buf)
+					    struct kobj_attribute *attr, char *buf)
 {
 	return sysfs_emit(buf, "%d.%d\n",
 			NILFS_CURRENT_REV, NILFS_MINOR_REV);
@@ -1087,7 +1087,7 @@ static const char features_readme_str[] =
 	"(1) revision\n\tshow current revision of NILFS file system driver.\n";
 
 static ssize_t nilfs_feature_README_show(struct kobject *kobj,
-					 struct attribute *attr,
+					 struct kobj_attribute *attr,
 					 char *buf)
 {
 	return sysfs_emit(buf, features_readme_str);

fs/nilfs2/sysfs.h

@@ -50,16 +50,16 @@ struct nilfs_sysfs_dev_subgroups {
 	struct completion sg_segments_kobj_unregister;
 };
 
-#define NILFS_COMMON_ATTR_STRUCT(name) \
+#define NILFS_KOBJ_ATTR_STRUCT(name) \
 struct nilfs_##name##_attr { \
 	struct attribute attr; \
-	ssize_t (*show)(struct kobject *, struct attribute *, \
+	ssize_t (*show)(struct kobject *, struct kobj_attribute *, \
 			char *); \
-	ssize_t (*store)(struct kobject *, struct attribute *, \
+	ssize_t (*store)(struct kobject *, struct kobj_attribute *, \
 			 const char *, size_t); \
 }
 
-NILFS_COMMON_ATTR_STRUCT(feature);
+NILFS_KOBJ_ATTR_STRUCT(feature);
 
 #define NILFS_DEV_ATTR_STRUCT(name) \
 struct nilfs_##name##_attr { \