From: Matt Helsley <matthltc@us.ibm.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Matt Helsley <matthltc@us.ibm.com>,
Alexey Dobriyan <adobriyan@gmail.com>,
Cyrill Gorcunov <gorcunov@openvz.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Kees Cook <keescook@chromium.org>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
Pavel Emelyanov <xemul@parallels.com>, Tejun Heo <tj@kernel.org>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/1] turn mm->exe_file into mm->exe_path
Date: Mon, 5 Mar 2012 13:14:36 -0800 [thread overview]
Message-ID: <20120305211436.GM7666@count0.beaverton.ibm.com> (raw)
In-Reply-To: <20120305152826.GA12419@redhat.com>
On Mon, Mar 05, 2012 at 04:28:26PM +0100, Oleg Nesterov wrote:
> I think the patch is simple and self-explanatory, it simply
> does s/mm->exe_file/mm->exe_path/.
>
> Why do we need mm->exe_file? IIUC, there are 2 reasons:
>
> 1. we do not want O(n) proc/pid/exe looking for the 1st
> VM_EXECUTABLE vma.
(Frankly this always seemed like a bit of a hack to me. If someone got
creative with text layout then it could break this hack...)
>
> 2. we do not want to rely on vma->vm_file->f_path,
> bprm->file->f_op->mmap can change ->vm_file.
>
> Unless there was another subtle reason, "struct path *exe_path"
> can equally work but it looks more clear.
PATCH 1/1 looks fine. I think Alexey Dobriyan was working on a similar
patch years ago.
> And can't we also remove added_exe_file_vma/removed_exe_file_vma?
> Why do we need mm->num_exe_file_vmas? Afaics it is only needed to
> "free" mm->exe_file if the application unmaps all these vmas. Say,
> to allow to unmount fs.
Yup. I know it's not pretty to have to track the exe file refs this way
but I couldn't see any other way to keep a reference to the file (or
path) and avoid pinning the mounted filesystem the exectuable is on.
> Can't we simply add PR_CLEAR_MM_EXE_PATH instead? Of course it is
> not enough if ->vm_file still has a reference. But c/r people want
Relying solely on this prctl would break existing programs. I believe Al
Viro's example was a program that copies its text to a new executable
area, unmaps the original, performs a pivot_root(), and finally umounts
the old root. Removing the counter would cause the mount to be pinned
for these programs and the umount would fail.
> PR_SET_MM_EXE_FILE anyway, see http://marc.info/?t=133052865500016
> So perhaps we can add PR_SET_MM_EXE_PATH which accepts NULL as well
> and kill this counter?
>
> Oleg.
Cheers,
-Matt Helsley
next prev parent reply other threads:[~2012-03-05 21:14 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-03-05 15:28 [PATCH 0/1] turn mm->exe_file into mm->exe_path Oleg Nesterov
2012-03-05 15:28 ` [PATCH 1/1] " Oleg Nesterov
2012-03-05 17:05 ` [PATCH 0/1] " Cyrill Gorcunov
2012-03-05 17:33 ` Oleg Nesterov
2012-03-05 18:25 ` Cyrill Gorcunov
2012-03-05 21:14 ` Matt Helsley [this message]
2012-03-06 16:28 ` Oleg Nesterov
2012-03-06 16:41 ` Cyrill Gorcunov
2012-03-06 18:16 ` Matt Helsley
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20120305211436.GM7666@count0.beaverton.ibm.com \
--to=matthltc@us.ibm.com \
--cc=adobriyan@gmail.com \
--cc=akpm@linux-foundation.org \
--cc=ebiederm@xmission.com \
--cc=gorcunov@openvz.org \
--cc=keescook@chromium.org \
--cc=kosaki.motohiro@jp.fujitsu.com \
--cc=linux-kernel@vger.kernel.org \
--cc=oleg@redhat.com \
--cc=tj@kernel.org \
--cc=xemul@parallels.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).