Re: [PATCH v8 2/5] ipc: IPCMNI limit check for semmni

[Davidlohr Bueso]

On Mon, 18 Jun 2018, Waiman Long wrote:

> For SysV semaphores, the semmni value is the last part of the 4-element
> sem number array. To make semmni behave in a similar way to msgmni and
> shmmni, we can't directly use the _minmax handler. Instead, a special
> sem specific handler is added to check the last argument to make sure
> that it is limited to the [0, IPCMNI] range. An error will be returned
> if this is not the case.
>
> Signed-off-by: Waiman Long <longman@xxxxxxxxxx>

Reviewed-by: Davidlohr Bueso <dave@xxxxxxxxxxxx>

> ---
> ipc/ipc_sysctl.c | 23 ++++++++++++++++++++++-
> ipc/util.h       |  9 +++++++++
> 2 files changed, 31 insertions(+), 1 deletion(-)
>
> diff --git a/ipc/ipc_sysctl.c b/ipc/ipc_sysctl.c
> index f87cb29..49f9bf4 100644
> --- a/ipc/ipc_sysctl.c
> +++ b/ipc/ipc_sysctl.c
> @@ -88,12 +88,33 @@ 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, semmni;
> +	struct ipc_namespace *ns = current->nsproxy->ipc_ns;
> +
> +	semmni = ns->sem_ctls[3];
> +	ret = proc_ipc_dointvec(table, write, buffer, lenp, ppos);
> +
> +	if (!ret)
> +		ret = sem_check_semmni(current->nsproxy->ipc_ns);
> +
> +	/*
> +	 * Reset the semmni value if an error happens.
> +	 */
> +	if (ret)
> +		ns->sem_ctls[3] = semmni;
> +	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;
> @@ -175,7 +196,7 @@ 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,
> 	},
> #ifdef CONFIG_CHECKPOINT_RESTORE
> 	{
> diff --git a/ipc/util.h b/ipc/util.h
> index 0aba323..8e9c52c 100644
> --- a/ipc/util.h
> +++ b/ipc/util.h
> @@ -218,6 +218,15 @@ int ipcget(struct ipc_namespace *ns, struct ipc_ids *ids,
> void free_ipcs(struct ipc_namespace *ns, struct ipc_ids *ids,
> 		void (*free)(struct ipc_namespace *, struct kern_ipc_perm *));
>
> +static inline int sem_check_semmni(struct ipc_namespace *ns) {
> +	/*
> +	 * Check semmni range [0, IPCMNI]
> +	 * semmni is the last element of sem_ctls[4] array
> +	 */
> +	return ((ns->sem_ctls[3] < 0) || (ns->sem_ctls[3] > IPCMNI))
> +		? -ERANGE : 0;
> +}
> +
> #ifdef CONFIG_COMPAT
> #include <linux/compat.h>
> struct compat_ipc_perm {
> --
> 1.8.3.1