Date: Tue, 9 May 2017 23:53:01 -0700 From: Christoph Hellwig <hch@...radead.org> To: Al Viro <viro@...IV.linux.org.uk> Cc: Christoph Hellwig <hch@...radead.org>, Andy Lutomirski <luto@...nel.org>, Ingo Molnar <mingo@...nel.org>, Greg KH <greg@...ah.com>, Thomas Garnier <thgarnie@...gle.com>, Martin Schwidefsky <schwidefsky@...ibm.com>, Heiko Carstens <heiko.carstens@...ibm.com>, Dave Hansen <dave.hansen@...el.com>, Arnd Bergmann <arnd@...db.de>, Thomas Gleixner <tglx@...utronix.de>, David Howells <dhowells@...hat.com>, René Nyffenegger <mail@...enyffenegger.ch>, Andrew Morton <akpm@...ux-foundation.org>, "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>, "Eric W . Biederman" <ebiederm@...ssion.com>, Oleg Nesterov <oleg@...hat.com>, Pavel Tikhomirov <ptikhomirov@...tuozzo.com>, Ingo Molnar <mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>, Paolo Bonzini <pbonzini@...hat.com>, Rik van Riel <riel@...hat.com>, Kees Cook <keescook@...omium.org>, Josh Poimboeuf <jpoimboe@...hat.com>, Borislav Petkov <bp@...en8.de>, Brian Gerst <brgerst@...il.com>, "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>, Christian Borntraeger <borntraeger@...ibm.com>, Russell King <linux@...linux.org.uk>, Will Deacon <will.deacon@....com>, Catalin Marinas <catalin.marinas@....com>, Mark Rutland <mark.rutland@....com>, James Morse <james.morse@....com>, linux-s390 <linux-s390@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, Linux API <linux-api@...r.kernel.org>, the arch/x86 maintainers <x86@...nel.org>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, Kernel Hardening <kernel-hardening@...ts.openwall.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Peter Zijlstra <a.p.zijlstra@...llo.nl> Subject: Re: Re: [PATCH v9 1/4] syscalls: Verify address limit before returning to user-mode On Wed, May 10, 2017 at 04:12:54AM +0100, Al Viro wrote: > What's the point? What's wrong with having kernel_read()/kernel_readv()/etc.? > You still have set_fs() in there; doing that one level up in call chain would > be just fine... IDGI. The problem is that they modify the address limit, which the whole subthread here wants to get rid of. > Broken commit: "net: don't play with address limits in kernel_recvmsg". > It would be OK if it was only about data. Unfortunately, that's not > true in one case: svc_udp_recvfrom() wants ->msg_control. Dropped, but we'll need to fix that eventually. > Another delicate place: you can't assume that write() always advances > file position by its (positive) return value. btrfs stuff is sensitive > to that. If we don't want to assume that we need to pass pointer to pos to kernel_read/write. Which might be a good idea in general. > ashmem probably _is_ OK with demanding ->read_iter(), but I'm not sure > about blind asma->file->f_pos += ret. That's begging for races. Actually, > scratch that - it *is* racy. I think the proper fix is to not even bother to maintain f_pos of the backing file, as we don't ever use it - all reads from it pass in an explicit position anyway.
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