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SubjectRe: [PATCH v2 3/5] sysctl: Warn when a clamped sysctl parameter is set out of range
On Tue, Feb 27, 2018 at 03:49:49PM -0500, Waiman Long wrote:
> Even with clamped sysctl parameters, it is still not that straight
> forward to figure out the exact range of those parameters. One may
> try to write extreme parameter values to see if they get clamped.
> To make it easier, a warning with the expected range will now be
> printed in the kernel ring buffer when a clamped sysctl parameter
> receives an out of range value.
>
> Signed-off-by: Waiman Long <longman@redhat.com>
> ---
> include/linux/sysctl.h | 1 +
> kernel/sysctl.c | 55 ++++++++++++++++++++++++++++++++++++++++++--------
> 2 files changed, 48 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
> index eceeaee..4e4f74a2 100644
> --- a/include/linux/sysctl.h
> +++ b/include/linux/sysctl.h
> @@ -128,6 +128,7 @@ struct ctl_table
> * ctl_table flags (16 different flags, at most)
> */
> #define CTL_FLAGS_CLAMP_RANGE (1 << 0) /* Clamp to min/max range */
> +#define CTL_FLAGS_OOR_WARNED (1 << 1) /* Out-of-range warning issued */

With the enum set you can then kdocify this too.

> struct ctl_node {
> struct rb_node node;
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 2b2b30c..f9f3373 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -2515,36 +2515,54 @@ static int proc_dointvec_minmax_sysadmin(struct ctl_table *table, int write,
> * min: ptr to minimum allowable value
> * max: ptr to maximum allowable value
> * flags: ptr to flags
> + * name: sysctl parameter name
> */
> struct do_proc_dointvec_minmax_conv_param {
> int *min;
> int *max;
> uint16_t *flags;
> + const char *name;
> };
>
> static int do_proc_dointvec_minmax_conv(bool *negp, unsigned long *lvalp,
> int *valp,
> int write, void *data)
> {
> +#define SYSCTL_WARN_MSG \
> +"Kernel parameter \"%s\" was set out of range [%d, %d], clamped to %d.\n"

Please loose this define. What about a proc_ctl_warn() which takes the
parameters and then does the checks?

> +
> struct do_proc_douintvec_minmax_conv_param *param = data;
>
> if (write) {
> unsigned int val = *lvalp;
> + bool clamped = false;
> bool clamp = param->flags &&
> (*param->flags & CTL_FLAGS_CLAMP_RANGE);
>
> @@ -2623,24 +2649,36 @@ static int do_proc_douintvec_minmax_conv(unsigned long *lvalp,
> return -EINVAL;
>
> if (param->min && *param->min > val) {
> - if (clamp)
> + if (clamp) {
> val = *param->min;
> - else
> + clamped = true;
> + } else {
> return -ERANGE;
> + }
> }
> if (param->max && *param->max < val) {
> - if (clamp)
> + if (clamp) {
> val = *param->max;
> - else
> + clamped = true;
> + } else {
> return -ERANGE;
> + }
> }
> *valp = val;
> + if (clamped && param->name &&
> + !(*param->flags & CTL_FLAGS_OOR_WARNED)) {
> + pr_warn(SYSCTL_WARN_MSG, param->name,
> + param->min ? *param->min : 0,
> + param->max ? *param->max : UINT_MAX, val);
> + *param->flags |= CTL_FLAGS_OOR_WARNED;

Why not just use pr_warn_once()?

Luis

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