From: Willy Tarreau <w@1wt.eu>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Kees Cook <keescook@chromium.org>,
Dirk Steinmetz <public@rsjtdrjgfuzkfg.com>,
Michael Kerrisk-manpages <mtk.manpages@gmail.com>,
Serge Hallyn <serge.hallyn@ubuntu.com>,
Seth Forshee <seth.forshee@canonical.com>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Linux FS Devel <linux-fsdevel@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
"Eric W . Biederman" <ebiederm@xmission.com>,
Serge Hallyn <serge.hallyn@canonical.com>,
"security@kernel.org" <security@kernel.org>
Subject: Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids
Date: Wed, 4 Nov 2015 19:28:13 +0100 [thread overview]
Message-ID: <20151104182813.GE22318@1wt.eu> (raw)
In-Reply-To: <CALCETrWGMfuoURG5cQsZ7gu1+zZoN5HWGjfFu6sZjHpPEprmEA@mail.gmail.com>
On Wed, Nov 04, 2015 at 10:17:06AM -0800, Andy Lutomirski wrote:
> > That said I never feel completely comfortable with changing a file's
> > permissions this way, I always fear it could break backup/restore
> > applications. Let's imagine for a minute that a restore does this :
> >
> > extract(const char *file_name, int file_perms) {
> > fd = open(".tmpfile", O_CREAT, file_perms);
> > mmap(fd);
> > /* actually write file */
> > close(fd);
> > unlink(real_file_name);
> > rename(".tmpfile", file_name);
> > }
> >
> > Yes I know it's not safe to do the chmod before writing to the file
> > but we could imagine some situations where it makes sense to be done
> > this way (eg: if the file is put into a protected directory), and
> > anyway this possibility is provided by open() and creat() so it is
> > legitimate to imagine these ones could exist.
> >
> > Such a change would slightly modify semantics and affect such use cases
> > *if they exist*, just like using write() instead of mmap() would fail.
> > We could imagine having a sysctl to disable this strengthening, but it
> > is probably not the best solution for the long term either.
>
> I'd say that this is an acceptable breakage risk.
Yes probably.
> In any event, the
> potential for data loss is limited to a bit of the file mode,
When this bit is the one sudo's setuid, it becomes one of the most important
bits on the whole system :-)
> and
> restore apps like that really don't deserve to work in the first
> place.
I absolutely agree for this specific case. I just wanted to raise this
case so that we're sure not to oversee anything related to other similar
but more justified use cases.
Willy
next prev parent reply other threads:[~2015-11-04 18:28 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-10 14:59 [PATCH] namei: permit linking with CAP_FOWNER in userns Dirk Steinmetz
2015-10-20 14:09 ` Dirk Steinmetz
2015-10-27 14:33 ` Seth Forshee
2015-10-27 18:08 ` Dirk Steinmetz
2015-10-27 20:28 ` Serge Hallyn
2015-10-28 15:07 ` Dirk Steinmetz
2015-10-28 17:33 ` Serge Hallyn
2015-11-02 15:10 ` Dirk Steinmetz
2015-11-02 18:02 ` Serge Hallyn
2015-11-02 19:57 ` Andy Lutomirski
2015-11-03 0:39 ` [RFC] namei: prevent sgid-hardlinks for unmapped gids Dirk Steinmetz
2015-11-03 15:44 ` Serge Hallyn
2015-11-03 18:20 ` Kees Cook
2015-11-03 23:21 ` Dirk Steinmetz
2015-11-03 23:29 ` Kees Cook
2015-11-04 6:58 ` Willy Tarreau
2015-11-04 17:59 ` Andy Lutomirski
2015-11-04 18:15 ` Willy Tarreau
2015-11-04 18:17 ` Andy Lutomirski
2015-11-04 18:28 ` Willy Tarreau [this message]
2015-11-06 21:59 ` Kees Cook
2015-11-06 22:30 ` Andy Lutomirski
2015-11-07 0:11 ` Kees Cook
2015-11-07 0:16 ` Kees Cook
2015-11-07 0:48 ` Andy Lutomirski
2015-11-07 5:05 ` Kees Cook
2015-11-08 2:02 ` Theodore Ts'o
2015-11-10 15:08 ` Jan Kara
2015-11-19 20:11 ` Kees Cook
2015-11-19 21:57 ` Andy Lutomirski
2015-11-19 22:02 ` Dave Chinner
2015-11-20 0:11 ` Kees Cook
2015-11-04 14:46 ` Serge E. Hallyn
2015-10-27 21:04 ` [PATCH] namei: permit linking with CAP_FOWNER in userns Eric W. Biederman
2015-11-03 17:51 ` Kees Cook
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