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Message-ID: <20170510031254.GC390@ZenIV.linux.org.uk>
Date: Wed, 10 May 2017 04:12:54 +0100
From: Al Viro <viro@...IV.linux.org.uk>
To: Christoph Hellwig <hch@...radead.org>
Cc: 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>,
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the arch/x86 maintainers <x86@...nel.org>,
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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 03:45:24AM +0100, Al Viro wrote:
> FWIW, some parts of that queue are obviously sane; it's the conversions of
> kernel_write() and friends to ->read_iter/->write_iter() that are non-starters.
Egads... OK, I *have* misread what you are doing there. Your vfs_iter_read()
works for files sans ->read_iter(). For strange values of "works" - you
hardwire "it's either iovec or kvec iterator" into its calling conventions,
which is a trouble waiting to happen.
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.
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.
Another delicate place: you can't assume that write() always advances
file position by its (positive) return value. btrfs stuff is sensitive
to that.
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.
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