From: Willy Tarreau <w@1wt.eu>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>,
"security@kernel.org" <security@kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Oleg Nesterov <oleg@redhat.com>,
Al Viro <viro@zeniv.linux.org.uk>,
Linux FS Devel <linux-fsdevel@vger.kernel.org>,
Brad Spengler <spender@grsecurity.net>
Subject: Re: [PATCH v2] vfs: Tighten up linkat(..., AT_EMPTY_PATH)
Date: Thu, 22 Aug 2013 20:53:17 +0200 [thread overview]
Message-ID: <20130822185317.GI31117@1wt.eu> (raw)
In-Reply-To: <CA+55aFzXNU-eJ7KeZyv5YYKKtm8iorG-o3QtD7NXx0GTzuH+Bw@mail.gmail.com>
On Thu, Aug 22, 2013 at 11:48:10AM -0700, Linus Torvalds wrote:
> On Wed, Aug 21, 2013 at 12:14 PM, Andy Lutomirski <luto@amacapital.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.
I agreed, simply because the condition here is different from the one in /proc.
I have read some code last evening to try to understand how /proc/pid/fd
entries were granted access to various processes, because I would love to
see the same condition being used in both places. Unfortunately, it's beyond
my skills, and I stopped after my random attempts gave me some panics.
Willy
next prev parent reply other threads:[~2013-08-22 18:53 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-21 19:14 [PATCH v2] vfs: Tighten up linkat(..., AT_EMPTY_PATH) Andy Lutomirski
[not found] ` <CA+55aFxi-ps2f2M8xPhfbuQ0pToqupPrDsLi2+GPUK2sqdYfUw@mail.gmail.com>
[not found] ` <CALCETrW7+LcexA6v6RQDKhni_yJAduOmiSDneCpq3v8sPDvwUQ@mail.gmail.com>
2013-08-21 20:16 ` Willy Tarreau
2013-08-22 18:48 ` Linus Torvalds
2013-08-22 18:53 ` Willy Tarreau [this message]
2013-08-22 19:05 ` Andy Lutomirski
2013-08-22 19:23 ` Linus Torvalds
2013-08-22 20:10 ` Andy Lutomirski
2013-08-22 20:15 ` Willy Tarreau
2013-08-22 20:22 ` Andy Lutomirski
2013-08-22 20:44 ` Linus Torvalds
2013-08-22 20:48 ` Andy Lutomirski
2013-08-22 20:54 ` Linus Torvalds
2013-08-22 20:58 ` Andy Lutomirski
2013-08-23 1:07 ` Al Viro
2013-08-25 3:37 ` Al Viro
2013-08-25 7:26 ` Andy Lutomirski
2013-08-25 14:23 ` Al Viro
2013-08-25 17:04 ` Andy Lutomirski
2013-08-25 19:57 ` Linus Torvalds
2013-08-25 20:06 ` Al Viro
2013-08-25 20:23 ` Linus Torvalds
2013-08-26 17:37 ` Linus Torvalds
2013-08-26 18:07 ` Linus Torvalds
2013-08-26 18:11 ` Andy Lutomirski
2013-08-27 19:16 ` [RFC PATCH] fs: Add user_file_or_path_at and use it for truncate Andy Lutomirski
2013-08-27 19:32 ` Linus Torvalds
2013-08-27 20:28 ` Andy Lutomirski
2013-08-28 6:16 ` Al Viro
2013-08-28 16:24 ` Linus Torvalds
2013-08-28 19:04 ` Andy Lutomirski
2013-08-28 19:59 ` Al Viro
2013-08-28 21:07 ` Andy Lutomirski
2013-08-27 23:08 ` Al Viro
2013-08-27 23:13 ` Andy Lutomirski
2013-08-24 18:29 ` /proc/pid/fd && anon_inode_fops Oleg Nesterov
2013-08-24 21:24 ` Willy Tarreau
2013-08-25 5:23 ` Al Viro
2013-08-25 6:50 ` Willy Tarreau
2013-08-25 18:51 ` Linus Torvalds
2013-08-25 19:48 ` Oleg Nesterov
2013-08-25 20:05 ` Linus Torvalds
2013-08-26 15:33 ` Oleg Nesterov
2013-08-26 16:37 ` Oleg Nesterov
2013-08-26 17:54 ` [PATCH] proc: make proc_fd_permission() thread-friendly Oleg Nesterov
2013-08-26 18:09 ` Linus Torvalds
2013-08-26 19:35 ` Linus Torvalds
2013-08-26 20:20 ` Willy Tarreau
2013-08-27 15:05 ` Oleg Nesterov
2013-08-27 14:39 ` [PATCH 0/1] proc: make /proc/self point to thread Oleg Nesterov
2013-08-27 14:40 ` [PATCH 1/1] " Oleg Nesterov
2013-08-27 16:39 ` Linus Torvalds
2013-08-27 17:49 ` Oleg Nesterov
2013-08-27 18:15 ` Linus Torvalds
2013-08-27 18:28 ` Oleg Nesterov
[not found] ` <CALCETrXP-mYBPRon=0NzexW1FK1Qxz2+Bwv7-WeHBQpvW7ywRg@mail.gmail.com>
2013-08-27 15:45 ` [PATCH] proc: make proc_fd_permission() thread-friendly Oleg Nesterov
2013-08-26 18:32 ` Eric W. Biederman
2013-08-26 18:46 ` Oleg Nesterov
2013-08-26 18:56 ` Oleg Nesterov
2013-08-26 19:10 ` Eric W. Biederman
2013-08-27 14:53 ` Oleg Nesterov
2013-08-25 18:32 ` /proc/pid/fd && anon_inode_fops Linus Torvalds
2013-08-25 19:11 ` Al Viro
2013-08-25 19:17 ` Andy Lutomirski
2013-09-03 15:58 ` Pavel Machek
2013-08-25 15:45 ` Oleg Nesterov
2013-08-22 19:39 ` [PATCH v2] vfs: Tighten up linkat(..., AT_EMPTY_PATH) Willy Tarreau
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