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

[Ryusuke Konishi <konishi.ryusuke@gmail.com>]

From: Nathan Chancellor <nathan@kernel.org>

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.

Cc: stable@vger.kernel.org
Fixes: aebe17f68444 ("nilfs2: add /sys/fs/nilfs2/features group")
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202509021646.bc78d9ef-lkp@intel.com/
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
---
Hi Andrew,

Please apply this bug fix.
This fixes a control-flow integrity test failure in nilfs2's sysfs
recently discovered by the kernel test robot and identified by Nathan.

Thanks,
Ryusuke Konishi

 fs/nilfs2/sysfs.c | 4 ++--
 fs/nilfs2/sysfs.h | 8 ++++----
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/fs/nilfs2/sysfs.c b/fs/nilfs2/sysfs.c
index 14868a3dd592..bc52afbfc5c7 100644
--- a/fs/nilfs2/sysfs.c
+++ b/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);
diff --git a/fs/nilfs2/sysfs.h b/fs/nilfs2/sysfs.h
index 78a87a016928..d370cd5cce3f 100644
--- a/fs/nilfs2/sysfs.h
+++ b/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 { \
-- 
2.43.0