xfs: fix potential memory leak in mount option parsing

When specifying string type mount option (e.g., logdev)
several times in a mount, current option parsing may
cause memory leak. Hence, call kfree for previous one
in this case.
Signed-off-by: Chengguang Xu <cgxu519@icloud.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/xfs_super.c

@@ -250,6 +250,7 @@ xfs_parseargs(
 				return -EINVAL;
 			break;
 		case Opt_logdev:
+			kfree(mp->m_logname);
 			mp->m_logname = match_strdup(args);
 			if (!mp->m_logname)
 				return -ENOMEM;
@@ -258,6 +259,7 @@ xfs_parseargs(
 			xfs_warn(mp, "%s option not allowed on this system", p);
 			return -EINVAL;
 		case Opt_rtdev:
+			kfree(mp->m_rtname);
 			mp->m_rtname = match_strdup(args);
 			if (!mp->m_rtname)
 				return -ENOMEM;