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

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Date:   Fri, 18 May 2018 20:20:26 -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 8:15 PM Vasily Gorbik <gor@...ux.ibm.com> wrote:

> Commit be83bbf80682 ("mmap: introduce sane default mmap limits")
> introduced "pgoff" limits checks for mmap, considering fs max file size
> as upper limit, which made it impossible to mmap /proc/vmcore file
> contents above 2Gb (/proc/vmcore appears to be the only procfs file
> supporting mmap).

> Reuse MAX_LFS_FILESIZE as procfs s_maxbytes value.

Ugh. /proc is where a lot of problems *have* been.

Admittedly not as much as random drivers, but still. If proc doesn't set
s_maxbytes, then we should not raise it here magically, there might be
various /proc files that get offset accounting wrong.

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.

                Linus