DEVICE_STRING_ATTR_RO should be only used by device drivers since it
relies on `struct device` to use device_show_string() function. Using
this with non device code led to a kCFI violation:
> cat /sys/fs/tmpfs/features/casefold
[ 70.558496] CFI failure at kobj_attr_show+0x2c/0x4c (target: device_show_string+0x0/0x38; expected type: 0xc527b809)
Like the other filesystems, fix this by manually declaring the attribute
using kobj_attribute() and writing a proper show() function.
Also, leave macros for anyone that need to expand tmpfs sysfs' with
more attributes (as seen in fs/btrfs/sysfs.c).
Fixes: 5132f08bd332 ("tmpfs: Expose filesystem features via sysfs")
Reported-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Closes: https://lore.kernel.org/lkml/20241031051822.GA2947788@thelio-3990X/
Signed-off-by: André Almeida <andrealmeid@xxxxxxxxxx>
---
mm/shmem.c | 29 +++++++++++++++++++++++++++--
1 file changed, 27 insertions(+), 2 deletions(-)
diff --git a/mm/shmem.c b/mm/shmem.c
index b86f526a1cb1..6038e1d11987 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -5548,13 +5548,38 @@ struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,
EXPORT_SYMBOL_GPL(shmem_read_mapping_page_gfp);
#if defined(CONFIG_SYSFS) && defined(CONFIG_TMPFS)
+
+#define __INIT_KOBJ_ATTR(_name, _mode, _show, _store) \
+{ \
+ .attr = { .name = __stringify(_name), .mode = _mode }, \
+ .show = _show, \
+ .store = _store, \
+}
+
+#define TMPFS_ATTR_W(_name, _store) \
+ static struct kobj_attribute tmpfs_attr_##_name = \
+ __INIT_KOBJ_ATTR(_name, 0200, NULL, _store)
+
+#define TMPFS_ATTR_RW(_name, _show, _store) \
+ static struct kobj_attribute tmpfs_attr_##_name = \
+ __INIT_KOBJ_ATTR(_name, 0644, _show, _store)
+
+#define TMPFS_ATTR_RO(_name, _show) \
+ static struct kobj_attribute tmpfs_attr_##_name = \
+ __INIT_KOBJ_ATTR(_name, 0444, _show, NULL)
+
#if IS_ENABLED(CONFIG_UNICODE)
-static DEVICE_STRING_ATTR_RO(casefold, 0444, "supported");
+static ssize_t casefold_show(struct kobject *kobj, struct kobj_attribute *a,
+ char *buf)
+{
+ return sysfs_emit(buf, "supported\n");
+}
+TMPFS_ATTR_RO(casefold, casefold_show);
#endif
static struct attribute *tmpfs_attributes[] = {
#if IS_ENABLED(CONFIG_UNICODE)
- &dev_attr_casefold.attr.attr,
+ &tmpfs_attr_casefold.attr,
#endif
NULL
};
--
2.47.0
