On 11/13/2012 07:58 PM, Kees Cook wrote:
> Stop using spinlocks in the read path. Add RCU list to handle the readers.
>
> Signed-off-by: Kees Cook <keesc...@chromium.org>
Looks good to me
Acked-by: John Johansen <john.johan...@canonical.com>
> ---
> security/yama/yama_lsm.c | 43 ++++++++++++++++++++-----------------------
> 1 file changed, 20 insertions(+), 23 deletions(-)
>
> diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c
> index b4c2984..17da6ca 100644
> --- a/security/yama/yama_lsm.c
> +++ b/security/yama/yama_lsm.c
> @@ -30,6 +30,7 @@ struct ptrace_relation {
> struct task_struct *tracer;
> struct task_struct *tracee;
> struct list_head node;
> + struct rcu_head rcu;
> };
>
> static LIST_HEAD(ptracer_relations);
> @@ -48,32 +49,29 @@ static DEFINE_SPINLOCK(ptracer_relations_lock);
> static int yama_ptracer_add(struct task_struct *tracer,
> struct task_struct *tracee)
> {
> - int rc = 0;
> - struct ptrace_relation *added;
> - struct ptrace_relation *entry, *relation = NULL;
> + struct ptrace_relation *relation, *added;
>
> added = kmalloc(sizeof(*added), GFP_KERNEL);
> if (!added)
> return -ENOMEM;
>
> + added->tracee = tracee;
> + added->tracer = tracer;
> +
> spin_lock_bh(&ptracer_relations_lock);
> - list_for_each_entry(entry, &ptracer_relations, node)
> - if (entry->tracee == tracee) {
> - relation = entry;
> - break;
> + list_for_each_entry_rcu(relation, &ptracer_relations, node) {
> + if (relation->tracee == tracee) {
> + list_replace_rcu(&relation->node, &added->node);
> + kfree_rcu(relation, rcu);
> + goto out;
> }
> - if (!relation) {
> - relation = added;
> - relation->tracee = tracee;
> - list_add(&relation->node, &ptracer_relations);
> }
> - relation->tracer = tracer;
>
> - spin_unlock_bh(&ptracer_relations_lock);
> - if (added != relation)
> - kfree(added);
> + list_add_rcu(&added->node, &ptracer_relations);
>
> - return rc;
> +out:
> + spin_unlock_bh(&ptracer_relations_lock);
> + return 0;
> }
>
> /**
> @@ -84,15 +82,16 @@ static int yama_ptracer_add(struct task_struct *tracer,
> static void yama_ptracer_del(struct task_struct *tracer,
> struct task_struct *tracee)
> {
> - struct ptrace_relation *relation, *safe;
> + struct ptrace_relation *relation;
>
> spin_lock_bh(&ptracer_relations_lock);
> - list_for_each_entry_safe(relation, safe, &ptracer_relations, node)
> + list_for_each_entry_rcu(relation, &ptracer_relations, node) {
> if (relation->tracee == tracee ||
> (tracer && relation->tracer == tracer)) {
> - list_del(&relation->node);
> - kfree(relation);
> + list_del_rcu(&relation->node);
> + kfree_rcu(relation, rcu);
> }
> + }
> spin_unlock_bh(&ptracer_relations_lock);
> }
>
> @@ -217,11 +216,10 @@ static int ptracer_exception_found(struct task_struct
> *tracer,
> struct task_struct *parent = NULL;
> bool found = false;
>
> - spin_lock_bh(&ptracer_relations_lock);
> rcu_read_lock();
> if (!thread_group_leader(tracee))
> tracee = rcu_dereference(tracee->group_leader);
> - list_for_each_entry(relation, &ptracer_relations, node)
> + list_for_each_entry_rcu(relation, &ptracer_relations, node)
> if (relation->tracee == tracee) {
> parent = relation->tracer;
> found = true;
> @@ -231,7 +229,6 @@ static int ptracer_exception_found(struct task_struct
> *tracer,
> if (found && (parent == NULL || task_is_descendant(parent, tracer)))
> rc = 1;
> rcu_read_unlock();
> - spin_unlock_bh(&ptracer_relations_lock);
>
> return rc;
> }
>
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