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Message-ID: <CALCETrX+CP6e8bfhWBpan=37fuK=V0gEm+zeHQOmCOhcfr7Bqg@mail.gmail.com>
Date: Tue, 9 May 2017 18:59:41 -0700
From: Andy Lutomirski <luto@...nel.org>
To: Kees Cook <keescook@...omium.org>
Cc: Christoph Hellwig <hch@...radead.org>, Andy Lutomirski <luto@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>, Greg KH <greg@...ah.com>,
Heiko Carstens <heiko.carstens@...ibm.com>, LKML <linux-kernel@...r.kernel.org>,
David Howells <dhowells@...hat.com>, Dave Hansen <dave.hansen@...el.com>,
"H . Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
Pavel Tikhomirov <ptikhomirov@...tuozzo.com>, Peter Zijlstra <a.p.zijlstra@...llo.nl>,
linux-s390 <linux-s390@...r.kernel.org>, "the arch/x86 maintainers" <x86@...nel.org>,
Russell King <linux@...linux.org.uk>, Will Deacon <will.deacon@....com>,
Christian Borntraeger <borntraeger@...ibm.com>, René Nyffenegger <mail@...enyffenegger.ch>,
Catalin Marinas <catalin.marinas@....com>, "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
Rik van Riel <riel@...hat.com>, Arnd Bergmann <arnd@...db.de>, Brian Gerst <brgerst@...il.com>,
Borislav Petkov <bp@...en8.de>, Josh Poimboeuf <jpoimboe@...hat.com>, Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
Linux API <linux-api@...r.kernel.org>, Oleg Nesterov <oleg@...hat.com>,
James Morse <james.morse@....com>, "Eric W . Biederman" <ebiederm@...ssion.com>,
Martin Schwidefsky <schwidefsky@...ibm.com>, Paolo Bonzini <pbonzini@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>, Linus Torvalds <torvalds@...ux-foundation.org>,
Thomas Garnier <thgarnie@...gle.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: Re: [PATCH v9 1/4] syscalls: Verify address
limit before returning to user-mode
On Tue, May 9, 2017 at 4:31 PM, Kees Cook <keescook@...omium.org> wrote:
> On Tue, May 9, 2017 at 3:52 PM, Andy Lutomirski <luto@...capital.net> wrote:
>> On Tue, May 9, 2017 at 9:50 AM, Kees Cook <keescook@...omium.org> wrote:
>>> On Tue, May 9, 2017 at 9:03 AM, Christoph Hellwig <hch@...radead.org> wrote:
>>>> On Tue, May 09, 2017 at 06:02:50AM -0700, Christoph Hellwig wrote:
>>>>> On Tue, May 09, 2017 at 06:00:01AM -0700, Andy Lutomirski wrote:
>>>>> > fs/splice.c has some, ahem, interesting uses that have been the source
>>>>> > of nasty exploits in the past. Converting them to use iov_iter
>>>>> > properly would be really, really nice. Christoph, I don't suppose
>>>>> > you'd like to do that?
>>>>>
>>>>> I can take care of all the fs code including this one.
>>>>
>>>> I spent the afternoon hacking up where I'd like this to head. It's
>>>> completely untested as of now:
>>>>
>>>> http://git.infradead.org/users/hch/vfs.git/shortlog/refs/heads/setfs-elimination
>>>
>>> Ooooh yes! Nice work.
>>>
>>> I love this:
>>> http://git.infradead.org/users/hch/vfs.git/commitdiff/51e83f50f824ca23f5584c172138e6b7c2ff786d
>>> but I wonder what it'll cause out-of-tree code to do. I mean, I'd
>>> rather nothing out-of-tree be calling these, but I'd hate 3rd party
>>> hacks even more.
>>>
>>> http://git.infradead.org/users/hch/vfs.git/commitdiff/018e0e9030777121fe87e89d43066691e7366587
>>> This accidentally(?) removes the kernel-doc comments.
>>>
>>> http://git.infradead.org/users/hch/vfs.git/commitdiff/78b62c730254fc39fa888cdbdca08fde6e09a798
>>> Could this be made defensive? (Return 0 if ret wraps, for example?) I
>>> see what the comment says, but not everyone will read that. :(
>>>
>>> http://git.infradead.org/users/hch/vfs.git/commitdiff/a106276ca0294be054bc89ce97219933fe543df1
>>> Perhaps unconditionally set USER_DS on exit instead of retaining
>>> whatever was there?
>>
>> I don't like silent fixups. If we want to do this, we should BUG or
>> at least WARN, not just change the addr limit. But I'm also not
>> convinced it's indicative of an actual bug here.
>
> Nothing should enter that function with KERNEL_DS set, right?
>
> BUG_ON(get_fs() != USER_DS);
> set_fs(KERNEL_DS);
> ...
> set_fs(USER_DS);
>
It's not immediately obvious to me that this shouldn't happen. Why
not do it the way Christoph did and then, once the rest of set_fs() is
tamed, consider this change (or trying to mass-convert file_operations
implementations to get rid of it entirely)?
--Andy
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