linux-kernel - Re: [PATCH v7 1/4] ipc: IPCMNI limit check for msgmni and shmmni

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Message-ID: <20180507223910.GW27853@wotan.suse.de>
Date:   Mon, 7 May 2018 22:39:10 +0000
From:   "Luis R. Rodriguez" <mcgrof@...nel.org>
To:     Waiman Long <longman@...hat.com>
Cc:     "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-doc@...r.kernel.org,
        Al Viro <viro@...iv.linux.org.uk>,
        Matthew Wilcox <willy@...radead.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH v7 1/4] ipc: IPCMNI limit check for msgmni and shmmni

On Mon, May 07, 2018 at 04:59:09PM -0400, Waiman Long wrote:
> A user can write arbitrary integer values to msgmni and shmmni sysctl
> parameters without getting error, but the actual limit is really
> IPCMNI (32k). This can mislead users as they think they can get a
> value that is not real.
> 
> The right limits are now set for msgmni and shmmni so that the users
> will become aware if they set a value outside of the acceptable range.
> 
> Signed-off-by: Waiman Long <longman@...hat.com>
> ---
>  ipc/ipc_sysctl.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/ipc/ipc_sysctl.c b/ipc/ipc_sysctl.c
> index 8ad93c2..f87cb29 100644
> --- a/ipc/ipc_sysctl.c
> +++ b/ipc/ipc_sysctl.c
> @@ -99,6 +99,7 @@ static int proc_ipc_auto_msgmni(struct ctl_table *table, int write,
>  static int zero;
>  static int one = 1;
>  static int int_max = INT_MAX;
> +static int ipc_mni = IPCMNI;
>  
>  static struct ctl_table ipc_kern_table[] = {
>  	{
> @@ -120,7 +121,9 @@ static int proc_ipc_auto_msgmni(struct ctl_table *table, int write,
>  		.data		= &init_ipc_ns.shm_ctlmni,
>  		.maxlen		= sizeof(init_ipc_ns.shm_ctlmni),
>  		.mode		= 0644,
> -		.proc_handler	= proc_ipc_dointvec,
> +		.proc_handler	= proc_ipc_dointvec_minmax,
> +		.extra1		= &zero,
> +		.extra2		= &ipc_mni,
>  	},
>  	{
>  		.procname	= "shm_rmid_forced",
> @@ -147,7 +150,7 @@ static int proc_ipc_auto_msgmni(struct ctl_table *table, int write,
>  		.mode		= 0644,
>  		.proc_handler	= proc_ipc_dointvec_minmax,
>  		.extra1		= &zero,
> -		.extra2		= &int_max,
> +		.extra2		= &ipc_mni,
>  	},
>  	{
>  		.procname	= "auto_msgmni",
> -- 
> 1.8.3.1

It seems negative values are not allowed, if true then having
a caller to use proc_douintvec_minmax() would help with ensuring
no invalid negative input values are used as well.

  Luis