linux-kernel - Re: [PATCH] init: use KERNEL_DS when trying to start init process

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

Message-ID: <BANLkTi=qBx0Mk=b2wsA3RZVKk0RUckeN6g@mail.gmail.com>
Date:	Wed, 8 Jun 2011 14:14:56 +0200
From:	Mathias Krause <minipli@...glemail.com>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, stable@...nel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	"David S. Miller" <davem@...emloft.net>,
	Chris Metcalf <cmetcalf@...era.com>,
	Chris Zankel <chris@...kel.net>
Subject: Re: [PATCH] init: use KERNEL_DS when trying to start init process

On Wed, Jun 8, 2011 at 12:47 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
> On Tue, Jun 07, 2011 at 07:00:24PM -0700, Linus Torvalds wrote:
>
>> That said, that commit (it's commit ID 4095b99c09e3d in tglx's tree)
>> predates the "real" BK history too: it's part of the (limited) 2.4.x
>> history that was imported from the release patches into BK at the
>> beginning of the use of BK. So at that point we didn't do indivual
>> commits, it's just the import of the v2.4.3.7 -> v2.4.3.8 patch.
>>
>> But yeah, it's old and crufty. And I agree that usually the correct
>> fix is to remove the set_fs() calls entirely.
>
> I think these days its job is done by start_thread(), which is where we
> switch to USER_DS; it's called by ->load_binary() when it decides it's past
> the point of no return.  However, it would be a good idea to verify that
> all architectures do it there properly and we are not exposing a hole by
> removal of this set_fs()...

I've checked all implementations of start_thread() and found some candidates:

SPARC, TILE and Xtensa don't call set_fs(USER_DS), albeit have
different definitions for USER_DS and KERNEL_DS. So those might need
fixing. I'm not familiar with those architectures, so someone else has
to answer this.

Score does not call set_fs(USER_DS) either but that's no problem
because USER_DS has the same value as KERNEL_DS on this architecture.

All others call set_fs(USER_DS) as almost the very first instruction
in start_thread(), or, as for MIPS, do it by setting addr_limit
directly.

Generally, I think, we should get Acks for the questionable arch
maintainers before commiting the patch that removes the call to
set_fs() in search_binary_handler().

I've also checked all binary format handlers if they all call
start_thread() and found a few that do not (binfmt_em86, binfmt_misc
and binfmt_script). But those are just interpreter warppers, i.e. call
search_binary_handler() in the end so should be safe.

Mathias
--
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/