[PATCH v2] ntfs: fix missing kstrdup() error check in ntfs_write_volume_label()

[Zhan Xusheng <zhanxusheng1024@gmail.com>]

ntfs_write_volume_label() does not check the return value of
kstrdup().  If the allocation fails, vol->volume_label is set to
NULL while the function returns success.  A subsequent
FS_IOC_GETFSLABEL then returns an empty string even though the
on-disk label was updated correctly.

Fix by allocating the new label before taking vol_ni->mrec_lock and
updating any on-disk metadata, so an -ENOMEM from kstrdup() leaves
both the in-memory and on-disk labels untouched and consistent.  On
success the preallocated copy replaces the old vol->volume_label.
Also move mark_inode_dirty_sync() into the success path so that it
is not called when no metadata was actually modified.

Fixes: 6251f0b0de7d ("ntfs: update super block operations")
Suggested-by: Hyunchul Lee <hyc.lee@gmail.com>
Signed-off-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
---
 fs/ntfs/super.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/fs/ntfs/super.c b/fs/ntfs/super.c
index 22dc7865eca7..ba99c497ee38 100644
--- a/fs/ntfs/super.c
+++ b/fs/ntfs/super.c
@@ -413,6 +413,7 @@ int ntfs_write_volume_label(struct ntfs_volume *vol, char *label)
 {
 	struct ntfs_inode *vol_ni = NTFS_I(vol->vol_ino);
 	struct ntfs_attr_search_ctx *ctx;
+	char *new_label;
 	__le16 *uname;
 	int uname_len, ret;
 
@@ -425,7 +426,7 @@ int ntfs_write_volume_label(struct ntfs_volume *vol, char *label)
 		return uname_len;
 	}
 
-	if (uname_len  > NTFS_MAX_LABEL_LEN) {
+	if (uname_len > NTFS_MAX_LABEL_LEN) {
 		ntfs_error(vol->sb,
 			   "Volume label is too long (max %d characters).",
 			   NTFS_MAX_LABEL_LEN);
@@ -433,11 +434,22 @@ int ntfs_write_volume_label(struct ntfs_volume *vol, char *label)
 		return -EINVAL;
 	}
 
+	/*
+	 * Allocate the in-memory label copy up front. If kstrdup() fails we
+	 * bail out before touching on-disk metadata, so the in-memory label
+	 * and the on-disk label stay in sync.
+	 */
+	new_label = kstrdup(label, GFP_KERNEL);
+	if (!new_label) {
+		kvfree(uname);
+		return -ENOMEM;
+	}
+
 	mutex_lock(&vol_ni->mrec_lock);
 	ctx = ntfs_attr_get_search_ctx(vol_ni, NULL);
 	if (!ctx) {
 		ret = -ENOMEM;
-		goto  out;
+		goto out;
 	}
 
 	if (!ntfs_attr_lookup(AT_VOLUME_NAME, NULL, 0, 0, 0, NULL, 0,
@@ -450,12 +462,14 @@ int ntfs_write_volume_label(struct ntfs_volume *vol, char *label)
 out:
 	mutex_unlock(&vol_ni->mrec_lock);
 	kvfree(uname);
-	mark_inode_dirty_sync(vol->vol_ino);
 
 	if (ret >= 0) {
 		kfree(vol->volume_label);
-		vol->volume_label = kstrdup(label, GFP_KERNEL);
+		vol->volume_label = new_label;
+		mark_inode_dirty_sync(vol->vol_ino);
 		ret = 0;
+	} else {
+		kfree(new_label);
 	}
 	return ret;
 }
-- 
2.43.0