netdev - RE: Buggy commit tracked to: "Re: [PATCH 2/9] iov_iter: move rw_copy_check_uvector() into lib/iov

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Message-ID: <134f162d711d466ebbd88906fae35b33@AcuMS.aculab.com>
Date:   Fri, 23 Oct 2020 12:46:36 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Greg KH' <gregkh@...uxfoundation.org>,
        David Hildenbrand <david@...hat.com>
CC:     Al Viro <viro@...iv.linux.org.uk>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Christoph Hellwig <hch@....de>,
        "kernel-team@...roid.com" <kernel-team@...roid.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>, Arnd Bergmann <arnd@...db.de>,
        David Howells <dhowells@...hat.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
        "linux-parisc@...r.kernel.org" <linux-parisc@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>,
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        <linux-security-module@...r.kernel.org>
Subject: RE: Buggy commit tracked to: "Re: [PATCH 2/9] iov_iter: move
 rw_copy_check_uvector() into lib/iov_iter.c"

From: Greg KH <gregkh@...uxfoundation.org>
> Sent: 22 October 2020 14:51

I've rammed the code into godbolt.

https://godbolt.org/z/9v5PPW

Definitely a clang bug.

Search for [wx]24 in the clang output.
nr_segs comes in as w2 and the initial bound checks are done on w2.
w24 is loaded from w2 - I don't believe this changes the high bits.
There are no references to w24, just x24.
So the kmalloc_array() is passed 'huge' and will fail.
The iov_iter_init also gets the 64bit value.

Note that the gcc code has a sign-extend copy of w2.

	David

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