On Thu, 1 Mar 2018 12:43:37 -0500 Waiman Long <longman@xxxxxxxxxx> wrote: > When minimum/maximum values are specified for a sysctl parameter in > the ctl_table structure with proc_dointvec_minmax() handler, update > to that parameter will fail with error if the given value is outside > of the required range. > > There are use cases where it may be better to clamp the value of > the sysctl parameter to the given range without failing the update, > especially if the users are not aware of the actual range limits. > Reading the value back after the update will now be a good practice > to see if the provided value exceeds the range limits. > > To provide this less restrictive form of range checking, a new flags > field is added to the ctl_table structure. The new field is a 16-bit > value that just fits into the hole left by the 16-bit umode_t field > without increasing the size of the structure. > > When the CTL_FLAGS_CLAMP_RANGE flag is set in the ctl_table entry, > any update from the userspace will be clamped to the given range > without error. > > ... > > --- a/include/linux/sysctl.h > +++ b/include/linux/sysctl.h > @@ -116,6 +116,7 @@ struct ctl_table > void *data; > int maxlen; > umode_t mode; > + uint16_t flags; It would be nice to make this have type `enum ctl_table_flags', but I guess there's then no reliable way of forcing it to be 16-bit. I guess this is the best we can do... --- a/include/linux/sysctl.h~sysctl-add-flags-to-support-min-max-range-clamping-fix +++ a/include/linux/sysctl.h @@ -116,7 +116,7 @@ struct ctl_table void *data; int maxlen; umode_t mode; - uint16_t flags; + uint16_t flags; /* enum ctl_table_flags */ struct ctl_table *child; /* Deprecated */ proc_handler *proc_handler; /* Callback for text formatting */ struct ctl_table_poll *poll; @@ -125,7 +125,7 @@ struct ctl_table } __randomize_layout; /** - * enum ctl_table_flags - flags for the ctl table + * enum ctl_table_flags - flags for the ctl table (struct ctl_table.flags) * * @CTL_FLAGS_CLAMP_RANGE: Set to indicate that the entry should be * flexibly clamped to min/max range in case the user provided > struct ctl_table *child; /* Deprecated */ > proc_handler *proc_handler; /* Callback for text formatting */ > struct ctl_table_poll *poll;
