linux-kernel - Re: [PATCH 2.6.29.6 - 2.6.35-rc3] CRED: Release spinlock before commit

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:	Fri, 18 Jun 2010 16:45:43 +0100
From:	David Howells <dhowells@...hat.com>
To:	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:	dhowells@...hat.com, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org
Subject: Re: [PATCH 2.6.29.6 - 2.6.35-rc3] CRED: Release spinlock before commit_creds().

Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp> wrote:

> reparent_to_kthreadd() is calling commit_creds() with tasklist_lock held.
> But commit_creds() calls
> key_fsuid_changed()/key_fsgid_changed()/proc_id_connector() which may sleep.
> Release tasklist_lock before calling commit_creds().

Hmmm...  Does this change leave a hole in which the thread can be accessed as
it's not locked away, but still has the old credentials?

I wonder if we should have an internal CLONE_KTHREAD flag to achieve this in
do_fork() rather than daemonize()'ing the thread later.

Also, key_fsuid_changed() and key_fsgid_changed() should be skipped in
commit_creds() if the thread-keyring pointer in the new creds is not the same
as that in the old creds (as will be the case if we're shifting to init_cred),
so they shouldn't really be a problem.

However, I can't see an easy way around proc_id_connector() sleeping - unless
we just don't call it if new == &init_cred in commit_creds().

I suppose it also leaves a hole if we call commit_creds() first, before
getting the write_lock()... :-/

David
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/