Re: [PATCH 4/4] quota: simplify the quotactl compat handling

On Sun, Jul 26, 2020 at 06:34:22PM +0200, Christoph Hellwig wrote:

On Sun, Jul 26, 2020 at 05:32:14PM +0100, Al Viro wrote:

quoted

quoted

+static int compat_copy_fs_qfilestat(struct compat_fs_qfilestat __user *to,
+		struct fs_qfilestat *from)
+{
+	if (copy_to_user(to, from, sizeof(*to)) ||
+	    put_user(from->qfs_nextents, &to->qfs_nextents))
+		return -EFAULT;
+	return 0;
+}

do we have any need of that put_user()?  Note that you don't even call
that thing unless compat_need_64bit_alignment_fixup() is true.  And AFAICS
all such cases are little-endian...

The main reason it is there is to preserve the previous semantics.
And no, I don't think we actually need it on x86.  But what if some
poor souls adds a BE version that needs this?  E.g. arm oabi has similar
weird alignment, and now imagine someone adding arm64 compat code for
that..

I'd probably add /* just in case some poor sod fucks up the same way for big-endian biarch */
next to that put_user(), then ;-)