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

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Date:   Mon, 7 May 2018 19:57:12 -0400
From:   Waiman Long <longman@...hat.com>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     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 05/07/2018 06:39 PM, Luis R. Rodriguez wrote:
> 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

Negative value doesn't mean sense here. So it is true that we can use
proc_douintvec_minmax() instead. However, the data types themselves are
defined as "int". So I think it is better to keep using
proc_dointvec_minmax() to be consistent with the data type.

Cheers,
Longman