linux-kernel - Re: [PATCH] procfs: fix mmap() for /proc/vmcore

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Message-ID: <CA+55aFwxEiiAC+dMMVqQ4igqb7rmn23Bq=BM8fqU=MFRWF1JSw@mail.gmail.com>
Date:   Fri, 18 May 2018 20:33:37 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     gor@...ux.ibm.com
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Heiko Carstens <heiko.carstens@...ibm.com>
Subject: Re: [PATCH] procfs: fix mmap() for /proc/vmcore

On Fri, May 18, 2018 at 8:20 PM Linus Torvalds <
torvalds@...ux-foundation.org> wrote:

> I'd *much* rather just set FMODE_UNSIGNED_OFFSET for /proc/vmcore _only_,
> rather than open up all proc files to issues with 4G+ offsets.

Hmm. I was going to point to the s_maxbytes check in rw_verify_area() and
ask you how that ever worked for that file, but it's not there, the
s_maxbyte checks are only in lseek and in do_splice().

So apparently we protect against llseek + read/write, but we don't protect
against pread64/pwrite64 having offset overflows..

That's crazy. That makes all the s_maxbytes protection much less effective
than it should be. Filesystems that don't get the 64-bit case right will
screw up pread64 and friends.

Al, I'm missing something. Did we always have this gaping hole where we
didn't actually check s_maxbytes against read/write, only
generic_file_llseek? Apparently.

               Linus