linux-kernel - Re: [PATCH v2] vfs: Tighten up linkat(..., AT_EMPTY

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Message-ID: <CA+55aFxaKGcpdxKXK_axqyFz_oCvFm1Q=_fJLq8di97x_-cCig@mail.gmail.com>
Date:	Sun, 25 Aug 2013 12:57:25 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	Andy Lutomirski <luto@...capital.net>, Willy Tarreau <w@....eu>,
	"security@...nel.org" <security@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	Brad Spengler <spender@...ecurity.net>
Subject: Re: [PATCH v2] vfs: Tighten up linkat(..., AT_EMPTY_PATH)

On Sat, Aug 24, 2013 at 8:37 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
>
> FWIW, I'm tempted to try the following trick:
>         * introduce FMODE_FLINK in file->f_mode; O_TMPFILE would set it,
> unless O_EXCL is present.
>         * introduce LOOKUP_LINK, to be passed by sys_linkat() when
> resolving the target.

[ .. snipped .. ]

Yes. I think we should do this, but I think we should also look at
what _other_ LOOKUP_xyz we should do for the /proc case.

For the read-only fd case, we should have a LOOKUP_WRITE flag, and
return -EPERM if an operation is a write, and we terminate in that
LAST_BIND case.

That would catch the truncate() case, but also the "open a read-only
fd for write or O_TRUNC" case.

Anything else? What other path operations matter that follow links
than truncate(), link() and open()?

                Linus
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