linux-kernel - Re: [PATCH v3 6/6] ipc: Clamp semmni to the real IPCMNI limit

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Date:   Thu, 8 Mar 2018 18:15:29 +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>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v3 6/6] ipc: Clamp semmni to the real IPCMNI limit

On Thu, Mar 01, 2018 at 12:43:40PM -0500, Waiman Long wrote:
> This patch clamps the semmni value (fourth element of sem_ctls[]
> array) to within the [0, IPCMNI] range and prints a warning message
> once when an out-of-range value is being written.
> 
> Signed-off-by: Waiman Long <longman@...hat.com>
> ---
>  ipc/ipc_sysctl.c | 13 ++++++++++++-
>  ipc/sem.c        | 28 ++++++++++++++++++++++++++++
>  ipc/util.h       |  4 ++++
>  3 files changed, 44 insertions(+), 1 deletion(-)
> 
> diff --git a/ipc/ipc_sysctl.c b/ipc/ipc_sysctl.c
> index 8eb7268..2c03f57 100644
> --- a/ipc/ipc_sysctl.c
> +++ b/ipc/ipc_sysctl.c
> @@ -97,12 +97,22 @@ static int proc_ipc_auto_msgmni(struct ctl_table *table, int write,
>  	return proc_dointvec_minmax(&ipc_table, write, buffer, lenp, ppos);
>  }
>  
> +static int proc_ipc_sem_dointvec(struct ctl_table *table, int write,
> +	void __user *buffer, size_t *lenp, loff_t *ppos)
> +{
> +	int ret = proc_ipc_dointvec(table, write, buffer, lenp, ppos);
> +
> +	sem_check_semmni(table, current->nsproxy->ipc_ns);
> +	return ret;
> +}
> +
>  #else
>  #define proc_ipc_doulongvec_minmax NULL
>  #define proc_ipc_dointvec	   NULL
>  #define proc_ipc_dointvec_minmax   NULL
>  #define proc_ipc_dointvec_minmax_orphans   NULL
>  #define proc_ipc_auto_msgmni	   NULL
> +#define proc_ipc_sem_dointvec	   NULL
>  #endif
>  
>  static int zero;
> @@ -186,7 +196,8 @@ static int proc_ipc_auto_msgmni(struct ctl_table *table, int write,
>  		.data		= &init_ipc_ns.sem_ctls,
>  		.maxlen		= 4*sizeof(int),
>  		.mode		= 0644,
> -		.proc_handler	= proc_ipc_dointvec,
> +		.proc_handler	= proc_ipc_sem_dointvec,
> +		.flags		= CTL_FLAGS_CLAMP_RANGE,
>  	},
>  #ifdef CONFIG_CHECKPOINT_RESTORE
>  	{
> diff --git a/ipc/sem.c b/ipc/sem.c
> index a4af049..739dfca 100644
> --- a/ipc/sem.c
> +++ b/ipc/sem.c
> @@ -2337,3 +2337,31 @@ static int sysvipc_sem_proc_show(struct seq_file *s, void *it)
>  	return 0;
>  }
>  #endif
> +
> +#ifdef CONFIG_PROC_SYSCTL
> +/*
> + * Check to see if semmni is out of range and clamp it if necessary.
> + */
> +void sem_check_semmni(struct ctl_table *table, struct ipc_namespace *ns)
> +{
> +	bool clamped = false;
> +
> +	if (!(table->flags & CTL_FLAGS_CLAMP_RANGE))
> +		return;
> +
> +	/*
> +	 * Clamp semmni to the range [0, IPCMNI].
> +	 */
> +	if (ns->sc_semmni < 0) {
> +		ns->sc_semmni = 0;
> +		clamped = true;
> +	}
> +	if (ns->sc_semmni > IPCMNI) {
> +		ns->sc_semmni = IPCMNI;
> +		clamped = true;
> +	}
> +	if (clamped)
> +		pr_warn_once("Kernel parameter \"sem[3]\" was set out of range [%d, %d], clamped to %d.\n",
> +			     0, IPCMNI, ns->sc_semmni);

Why are the users issuing a warning, wouldn't the API do the warning
on its own, specially since we're adding a warn flag?

  Luis