Date: Wed, 10 May 2017 03:45:24 +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>, 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 03:11:18AM +0100, Al Viro wrote: > On Tue, May 09, 2017 at 09:03:22AM -0700, Christoph Hellwig 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. > > Oh? > > > 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 > > And just what happens to driver that has no ->read_iter()? Unless I'm > seriously misreading that, NAK with extreme prejudice. 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. That stuff is used in too many situations; we can't guarantee that all of them will be for files that have those. As for default_file_splice_read(), I seriously suspect that with your change we could as well just make it return -EINVAL and be done with that; places that have ->read_iter() tend to have explicit ->splice_read() and it looks like the ones that do not should simply use generic_file_read_iter(). I hadn't checked that, but there's not a lot of those: arch/s390/hypfs/inode.c:437: .read_iter = hypfs_read_iter, drivers/char/mem.c:798: .read_iter = read_iter_null, drivers/char/mem.c:813: .read_iter = read_iter_zero, drivers/char/mem.c:824: .read_iter = read_iter_zero, drivers/char/raw.c:286: .read_iter = blkdev_read_iter, drivers/net/tap.c:1134: .read_iter = tap_read_iter, drivers/net/tun.c:2423: .read_iter = tun_chr_read_iter, drivers/usb/gadget/function/f_fs.c:1255: .read_iter = ffs_epfile_read_iter, drivers/usb/gadget/legacy/inode.c:703: .read_iter = ep_read_iter, drivers/vhost/net.c:1252: .read_iter = vhost_net_chr_read_iter, fs/9p/vfs_file.c:641: .read_iter = generic_file_read_iter, fs/9p/vfs_file.c:652: .read_iter = generic_file_read_iter, fs/9p/vfs_file.c:664: .read_iter = v9fs_file_read_iter, fs/9p/vfs_file.c:675: .read_iter = v9fs_file_read_iter, fs/9p/vfs_file.c:687: .read_iter = v9fs_mmap_file_read_iter, fs/9p/vfs_file.c:698: .read_iter = v9fs_mmap_file_read_iter, fs/fuse/cuse.c:180: .read_iter = cuse_read_iter, fs/fuse/file.c:3015: .read_iter = fuse_direct_read_iter, fs/hugetlbfs/inode.c:980: .read_iter = hugetlbfs_read_iter, fs/ncpfs/file.c:248: .read_iter = ncp_file_read_iter, fs/orangefs/file.c:742: .read_iter = orangefs_file_read_iter, fs/pipe.c:1011: .read_iter = pipe_read, sound/core/pcm_native.c:3696: .read_iter = snd_pcm_readv, is the full list and I'm fairly certain that most of them will work with generic_file_splice_read() just fine. drivers/char definitely will, so will ncpfs/orangefs/hugetlbfs/most of 9p ones (two of the latter might need some care in p9_client_read(), but that should be doable easily enough). pipe is irrelevant (->splice_read() won't be called for those). fuse ones should be doable, but that might take a bit more infrastructure work in lib/iov_iter.c. vhost, gadgetfs, tun/tap - no idea at the moment.
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