ntfs: serialize volume label accesses

commit e9e50ce4f13dc721014af622613409455c734942 upstream.

Protect vol->volume_label with a mutex and snaphost the label before
copy_to_user. This prevent a use-after-free when FS_IOC_SETFSLABEL
replaces the vol->volume_label and FS_IOC_GETTSLABEL reads it
concurrently.

Cc: stable@vger.kernel.org # v7.1
Signed-off-by: Hyunchul Lee <hyc.lee@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

3 files changed, 28 insertions, 10 deletions

diff --git a/fs/ntfs/file.c b/fs/ntfs/file.c
index e8bea22b81a7..264cf8404385 100644
--- a/fs/ntfs/file.c
+++ b/fs/ntfs/file.c
@@ -707,12 +707,21 @@ static int ntfs_ioctl_get_volume_label(struct file *filp, unsigned long arg)
 {
 	struct ntfs_volume *vol = NTFS_SB(file_inode(filp)->i_sb);
 	char __user *buf = (char __user *)arg;
+	char label[FSLABEL_MAX];
+	ssize_t len;
 
+	mutex_lock(&vol->volume_label_lock);
 	if (!vol->volume_label) {
-		if (copy_to_user(buf, "", 1))
-			return -EFAULT;
-	} else if (copy_to_user(buf, vol->volume_label,
-				MIN(FSLABEL_MAX, strlen(vol->volume_label) + 1)))
+		label[0] = '\0';
+		len = 0;
+	} else {
+		len = strscpy(label, vol->volume_label, sizeof(label));
+		if (len == -E2BIG)
+			len = FSLABEL_MAX - 1;
+	}
+	mutex_unlock(&vol->volume_label_lock);
+
+	if (copy_to_user(buf, label, len + 1))
 		return -EFAULT;
 	return 0;
 }
diff --git a/fs/ntfs/super.c b/fs/ntfs/super.c
index 9e321cc2febe..cb880cb6e388 100644
--- a/fs/ntfs/super.c
+++ b/fs/ntfs/super.c
@@ -460,17 +460,23 @@ int ntfs_write_volume_label(struct ntfs_volume *vol, char *label)
 	ret = ntfs_resident_attr_record_add(vol_ni, AT_VOLUME_NAME, AT_UNNAMED, 0,
 					    (u8 *)uname, uname_len * sizeof(__le16), 0);
 out:
-	mutex_unlock(&vol_ni->mrec_lock);
-	kvfree(uname);
-
 	if (ret >= 0) {
-		kfree(vol->volume_label);
+		char *old_label;
+
+		mutex_lock(&vol->volume_label_lock);
+		old_label = vol->volume_label;
 		vol->volume_label = new_label;
+		mutex_unlock(&vol->volume_label_lock);
+
+		kfree(old_label);
 		mark_inode_dirty_sync(vol->vol_ino);
 		ret = 0;
-	} else {
-		kfree(new_label);
 	}
+	mutex_unlock(&vol_ni->mrec_lock);
+	kvfree(uname);
+
+	if (ret < 0)
+		kfree(new_label);
 	return ret;
 }
 
@@ -2631,6 +2637,7 @@ static int ntfs_init_fs_context(struct fs_context *fc)
 	NVolSetCaseSensitive(vol);
 	init_rwsem(&vol->mftbmp_lock);
 	init_rwsem(&vol->lcnbmp_lock);
+	mutex_init(&vol->volume_label_lock);
 
 	fc->s_fs_info = vol;
 	fc->ops = &ntfs_context_ops;
diff --git a/fs/ntfs/volume.h b/fs/ntfs/volume.h
index af41427ec622..99e642f475f7 100644
--- a/fs/ntfs/volume.h
+++ b/fs/ntfs/volume.h
@@ -72,6 +72,7 @@
  * @vol_flags: Volume flags.
  * @major_ver: Ntfs major version of volume.
  * @minor_ver: Ntfs minor version of volume.
+ * @volume_label_lock: protects @volume_label.
  * @volume_label: volume label.
  * @root_ino: The VFS inode of the root directory.
  * @secure_ino: The VFS inode of $Secure (NTFS3.0+ only, otherwise NULL).
@@ -133,6 +134,7 @@ struct ntfs_volume {
 	struct inode *logfile_ino;
 	struct inode *lcnbmp_ino;
 	struct rw_semaphore lcnbmp_lock;
+	struct mutex volume_label_lock;
 	struct inode *vol_ino;
 	__le16 vol_flags;
 	u8 major_ver;