Re: [PATCH v4 2/4] sysctl: Move some boundary constants form sysctl.c to sysctl_vals

[Xiaoming Ni]

On 2020/5/19 12:44, Tetsuo Handa wrote:
On 2020/05/19 12:31, Xiaoming Ni wrote:
Some boundary (.extra1 .extra2) constants (E.g: neg_one two) in
sysctl.c are used in multiple features. Move these variables to
sysctl_vals to avoid adding duplicate variables when cleaning up
sysctls table.
Signed-off-by: Xiaoming Ni <nixiaom...@huawei.com>
Reviewed-by: Kees Cook <keesc...@chromium.org>

I feel that it is use of

        void *extra1;
        void *extra2;

in "struct ctl_table" that requires constant values indirection.
Can't we get rid of sysctl_vals using some "union" like below?

struct ctl_table {
        const char *procname;           /* Text ID for /proc/sys, or zero */
        void *data;
        int maxlen;
        umode_t mode;
        struct ctl_table *child;        /* Deprecated */
        proc_handler *proc_handler;     /* Callback for text formatting */
        struct ctl_table_poll *poll;
        union {
                void *min_max_ptr[2];
                int min_max_int[2];
                long min_max_long[2];
        };
} __randomize_layout;

.


net/decnet/dn_dev.c:
static void dn_dev_sysctl_register(struct net_device *dev, struct 
dn_dev_parms *parms)
{
        struct dn_dev_sysctl_table *t;
        int i;

        char path[sizeof("net/decnet/conf/") + IFNAMSIZ];

        t = kmemdup(&dn_dev_sysctl, sizeof(*t), GFP_KERNEL);
        if (t == NULL)
                return;

        for(i = 0; i < ARRAY_SIZE(t->dn_dev_vars) - 1; i++) {
                long offset = (long)t->dn_dev_vars[i].data;
                t->dn_dev_vars[i].data = ((char *)parms) + offset;
        }

        snprintf(path, sizeof(path), "net/decnet/conf/%s",
                dev? dev->name : parms->name);

        t->dn_dev_vars[0].extra1 = (void *)dev;

        t->sysctl_header = register_net_sysctl(&init_net, path, t->dn_dev_vars);
        if (t->sysctl_header == NULL)
                kfree(t);
        else
                parms->sysctl = t;
}

A small amount of code is not used as a boundary value when using 
extra1. This scenario may not be suitable for renaming to min_max_ptr.

Should we add const to extra1 extra2 ?

--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -124,8 +124,8 @@ struct ctl_table {
        struct ctl_table *child;        /* Deprecated */
        proc_handler *proc_handler;     /* Callback for text formatting */
        struct ctl_table_poll *poll;
-       void *extra1;
-       void *extra2;
+       const void *extra1;
+       const void *extra2;
 } __randomize_layout;


Thanks
Xiaoming Ni