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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