linux-kernel - Re: [PATCH 4.4 014/168] sysctl: handle overflow for file-max

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Date:   Thu, 25 Apr 2019 10:15:08 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Christian Brauner <christian@...uner.io>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        stable@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.4 014/168] sysctl: handle overflow for file-max

On Wed, Apr 24, 2019 at 11:50:22PM +0200, Christian Brauner wrote:
> On Wed, Apr 24, 2019 at 7:16 PM Greg Kroah-Hartman
> <gregkh@...uxfoundation.org> wrote:
> >
> > [ Upstream commit 32a5ad9c22852e6bd9e74bdec5934ef9d1480bc5 ]
> >
> > Currently, when writing
> >
> >   echo 18446744073709551616 > /proc/sys/fs/file-max
> >
> > /proc/sys/fs/file-max will overflow and be set to 0.  That quickly
> > crashes the system.
> >
> > This commit sets the max and min value for file-max.  The max value is
> > set to long int.  Any higher value cannot currently be used as the
> > percpu counters are long ints and not unsigned integers.
> >
> > Note that the file-max value is ultimately parsed via
> > __do_proc_doulongvec_minmax().  This function does not report error when
> > min or max are exceeded.  Which means if a value largen that long int is
> > written userspace will not receive an error instead the old value will be
> > kept.  There is an argument to be made that this should be changed and
> > __do_proc_doulongvec_minmax() should return an error when a dedicated min
> > or max value are exceeded.  However this has the potential to break
> > userspace so let's defer this to an RFC patch.
> >
> > Link: http://lkml.kernel.org/r/20190107222700.15954-3-christian@brauner.io
> > Signed-off-by: Christian Brauner <christian@...uner.io>
> > Acked-by: Kees Cook <keescook@...omium.org>
> > Cc: Alexey Dobriyan <adobriyan@...il.com>
> > Cc: Al Viro <viro@...iv.linux.org.uk>
> > Cc: Dominik Brodowski <linux@...inikbrodowski.net>
> > Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
> > Cc: Joe Lawrence <joe.lawrence@...hat.com>
> > Cc: Luis Chamberlain <mcgrof@...nel.org>
> > Cc: Waiman Long <longman@...hat.com>
> > [christian@...uner.io: v4]
> >   Link: http://lkml.kernel.org/r/20190210203943.8227-3-christian@brauner.io
> > Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> > Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
> > Signed-off-by: Sasha Levin <sashal@...nel.org>
> 
> Hey Greg,
> 
> Just an heads-up. This patch triggered a KASAN warning and Will has
> sent a fix for that
> which is already in master.
> So if you backport this patch you likely also want to backport
> 
> 9002b21465fa4d829edfc94a5a441005cffaa972
> 
> (See  https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9002b21465fa4d829edfc94a5a441005cffaa972
> )
> 
> Seems we missed a Cc: for stable in there. Sorry about that.

No problem, thanks for letting me know, now queued up everywhere.

greg k-h