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Message-ID: <CA+55aFzXNU-eJ7KeZyv5YYKKtm8iorG-o3QtD7NXx0GTzuH+Bw@mail.gmail.com>
Date: Thu, 22 Aug 2013 11:48:10 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Andy Lutomirski <luto@...capital.net>
Cc: "security@...nel.org" <security@...nel.org>,
Ingo Molnar <mingo@...nel.org>, Willy Tarreau <w@....eu>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Oleg Nesterov <oleg@...hat.com>,
Al Viro <viro@...iv.linux.org.uk>,
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 Wed, Aug 21, 2013 at 12:14 PM, Andy Lutomirski <luto@...capital.net> wrote:
>
> So let's be careful for now: only allow linkat(..., AT_EMPTY_PATH)
> if the target is I_LINKABLE.
So I really detest this just because it's such a special case. Now
this is only useful for that one special case, and the thing very
fundamentally checks that one special case in a place that is
impossible to check for the /proc case, so the proc case remains
totally separate.
Which just bothers me.
I think we could easily at least allow the "file->f_creds ==
current->creds" case (and yes, I literally mean comparing the pointers
- not only is it cheaper, but it literally means "nothing odd has
happened in between opening and the lookup").
And I'm wondering if we shouldn't actually do that at "path_init"
time. Right now the code says:
/* Caller must check execute permissions on the
starting path component */
struct fd f = fdget_raw(dfd);
and then uses the struct file mindlessly.
I'm wondering if we should just do some validation in that place, and say:
- for directories, we require exec permissions here
- for everything else, we require that f->f_cred == current->cred check.
I dunno. But that I_LINKABLE thing just bothers me. It screams "I'm
hacky" to me.
Linus
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