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

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Message-ID: <20180509193200.GU27853@wotan.suse.de>
Date:   Wed, 9 May 2018 19:32:00 +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 07:57:12PM -0400, Waiman Long wrote:
> 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.

Huh, no... If you *know* the valid values *are* only positive, the right
thing to do is to then *change* the data type. Tons of odd bugs can creep
up because of these stupid things.

  Luis