Re: [PATCH][SMACK] convert smack rule list to linux list

Paul E. McKenney
2009-02-22T15:31:19Z

On Sun, Feb 22, 2009 at 02:14:38PM +0100, etienne wrote:
> Tetsuo Handa wrote:
> > etienne wrote:
> >> diff --git a/security/smack/smack_access.c b/security/smack/smack_access.c
> >> index 2e0b83e..3dc312d 100644
> >> --- a/security/smack/smack_access.c
> >> +++ b/security/smack/smack_access.c
> >> @@ -87,7 +87,6 @@ static u32 smack_next_secid = 10;
> >> int smk_access(char *subject_label, char *object_label, int request)
> >> {
> >> u32 may = MAY_NOT;
> >> - struct smk_list_entry *sp;
> >> struct smack_rule *srp;
> >>
> >> /*
> >> @@ -139,8 +138,8 @@ int smk_access(char *subject_label, char *object_label, int request)
> >> * access (e.g. read is included in readwrite) it's
> >> * good.
> >> */
> >> - for (sp = smack_list; sp != NULL; sp = sp->smk_next) {
> >> - srp = &sp->smk_rule;
> >> +
> >> + list_for_each_entry(srp, &smack_rule_list, list) {
> >>
> >> if (srp->smk_subject == subject_label ||
> >> strcmp(srp->smk_subject, subject_label) == 0) {
> >
> > Use of standard doubly linked list requires a lock, doesn't it?
> > What lock protects smack_rule_list?
> >
> you're right;
>
> what's the best way, using a rcu variant for "list_for_each, container_of ...etc" ?
> (concurrent list insertion are already protected with a mutex, so rcu must the good idea for the read side)

You want list_for_each_entry_rcu() above. You will need list_add_rcu()
when adding elements to the list.

Again, if these elements are ever removed, you will need rcu_read_lock()
and rcu_read_unlock() surrounding their use. Otherwise, an element can
be freed out from under a reader who is still referencing it.

Thanx, Paul