From: stsp <stsp2@yandex.ru>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-kernel@vger.kernel.org,
"Stefan Metzmacher" <metze@samba.org>,
"Eric Biederman" <ebiederm@xmission.com>,
"Andy Lutomirski" <luto@kernel.org>,
"Christian Brauner" <brauner@kernel.org>,
"Jan Kara" <jack@suse.cz>, "Jeff Layton" <jlayton@kernel.org>,
"Chuck Lever" <chuck.lever@oracle.com>,
"Alexander Aring" <alex.aring@gmail.com>,
"David Laight" <David.Laight@aculab.com>,
linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Christian Göttsche" <cgzones@googlemail.com>
Subject: Re: [PATCH 2/2] openat2: add OA2_INHERIT_CRED flag
Date: Thu, 25 Apr 2024 10:24:37 +0300 [thread overview]
Message-ID: <d1686d9d-b403-4985-bcaa-41d4f45a8ac0@yandex.ru> (raw)
In-Reply-To: <20240425023127.GH2118490@ZenIV>
25.04.2024 05:31, Al Viro пишет:
> Consider the following, currently absolutely harmless situation:
> * process is owned by luser:students.
> * descriptor 69 refers to root-opened root directory (O_RDONLY)
> What's the expected result of
> fcntl(69, F_SEFTD, O_CLOEXEC);
> opening "etc/shadow" with dirfd equal to 69 and your flag given
> subsequent read() from the resulting descriptor?
>
> At which point will the kernel say "go fuck yourself, I'm not letting you
> read that file", provided that attacker passes that new flag of yours?
>
> As a bonus question, how about opening it for _write_, seeing that this
> is an obvious instant roothole?
>
> Again, currently the setup that has a root-opened directory in descriptor
> table of a non-root process is safe.
>
> Incidentally, suppose you have the same process run with stdin opened
> (r/o) by root. F_SETFD it to O_CLOEXEC, then use your open with
> dirfd being 0, pathname - "" and flags - O_RDWR.
Ok, F_SETFD, how simple. :(
> AFAICS, without an explicit opt-in by the original opener it's
> a non-starter, and TBH I doubt that even with such opt-in (FMODE_CRED,
> whatever) it would be a good idea - it gives too much.
Yes, which is why I am quite sceptical
to this FMODE_CRED idea.
Please note that my O_CLOEXEC check
actually meant to check that exactly this
process have opened the dir. It just didn't
happen that way, as you pointed.
Can I replace the O_CLOEXEC check with
some explicit check that makes sure the
fd was opened by exactly that process?
next prev parent reply other threads:[~2024-04-25 7:24 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-24 10:52 [PATCH v4 0/2] implement OA2_INHERIT_CRED flag for openat2() Stas Sergeev
2024-04-24 10:52 ` [PATCH 1/2] fs: reorganize path_openat() Stas Sergeev
2024-04-25 8:13 ` kernel test robot
2024-04-24 10:52 ` [PATCH 2/2] openat2: add OA2_INHERIT_CRED flag Stas Sergeev
2024-04-25 2:31 ` Al Viro
2024-04-25 7:24 ` stsp [this message]
2024-04-25 9:23 ` stsp
2024-04-25 13:50 ` kernel test robot
2024-04-25 14:02 ` Christian Brauner
2024-04-26 13:36 ` stsp
2024-04-24 16:09 ` [PATCH v4 0/2] implement OA2_INHERIT_CRED flag for openat2() Christian Brauner
2024-04-24 17:50 ` stsp
2024-04-25 9:54 ` Christian Brauner
2024-04-25 10:12 ` stsp
2024-04-25 12:08 ` Christian Brauner
2024-04-25 12:39 ` stsp
-- strict thread matches above, loose matches on Subject: below --
2024-04-23 22:46 [PATCH v3 " Stas Sergeev
2024-04-23 22:46 ` [PATCH 2/2] openat2: add OA2_INHERIT_CRED flag Stas Sergeev
2024-04-23 11:01 [PATCH v2 0/2] implement OA2_INHERIT_CRED flag for openat2() Stas Sergeev
2024-04-23 11:01 ` [PATCH 2/2] openat2: add OA2_INHERIT_CRED flag Stas Sergeev
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