linux-kernel - Re: [PATCH 03/11] fs: add new read_uptr and write

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Message-ID: <20200630070434.GA28654@lst.de>
Date:   Tue, 30 Jun 2020 09:04:34 +0200
From:   Christoph Hellwig <hch@....de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Christoph Hellwig <hch@....de>,
        David Laight <David.Laight@...lab.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Iurii Zaikin <yzaikin@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH 03/11] fs: add new read_uptr and write_uptr file
 operations

Next fund one, in net/ipv6/ip6_flowlabel.c:ipv6_flowlabel_opt() we
have this gem toward the end:

		if (!freq->flr_label) {
			if (copy_to_user(&((struct in6_flowlabel_req __user *)optval)->flr_label,
					 &fl->label, sizeof(fl->label))) {
				/* Intentionally ignore fault. */

so it writes back to what was supposed to be the input parameter,
and only does it for a partial region.  Not sure how we could handle
that with any kind of copy to kernel in the caller scheme?