Re: [PATCH 3/3] auditsc: Do not use RCU primitive to read from cred pointer

On Fri, Feb 7, 2020 at 1:08 PM Amol Grover <frextrite(a)gmail.com&gt; wrote: > > task_struct::cred is only used task-synchronously and does > not require any RCU locks, hence, rcu_dereference_check is > not required to read from it. > > Suggested-by: Jann Horn <jannh(a)google.com&gt; > Co-developed-by: Joel Fernandes (Google) <joel(a)joelfernandes.org&gt; > Signed-off-by: Joel Fernandes (Google) <joel(a)joelfernandes.org&gt; > Signed-off-by: Amol Grover <frextrite(a)gmail.com&gt; > --- > kernel/auditsc.c | 15 +++++---------- > 1 file changed, 5 insertions(+), 10 deletions(-) Considering the other changes in this patchset this change seems reasonable to me. I'm assuming you were intending this patchset to go in via some tree other than audit?

Acked-by: Paul Moore <paul(a)paul-moore.com&gt; > diff --git a/kernel/auditsc.c b/kernel/auditsc.c > index 4effe01ebbe2..d3510513cdd1 100644 > --- a/kernel/auditsc.c > +++ b/kernel/auditsc.c > @@ -430,24 +430,19 @@ static int audit_field_compare(struct task_struct *tsk, > /* Determine if any context name data matches a rule's watch data */ > /* Compare a task_struct with an audit_rule. Return 1 on match, 0 > * otherwise. > - * > - * If task_creation is true, this is an explicit indication that we are > - * filtering a task rule at task creation time. This and tsk == current are > - * the only situations where tsk->cred may be accessed without an rcu read lock. > */ > static int audit_filter_rules(struct task_struct *tsk, > struct audit_krule *rule, > struct audit_context *ctx, > struct audit_names *name, > - enum audit_state *state, > - bool task_creation) > + enum audit_state *state) > { > const struct cred *cred; > int i, need_sid = 1; > u32 sid; > unsigned int sessionid; > > - cred = rcu_dereference_check(tsk->cred, tsk == current || task_creation); > + cred = tsk->cred; > > for (i = 0; i < rule->field_count; i++) { > struct audit_field *f = &rule->fields[i]; > @@ -745,7 +740,7 @@ static enum audit_state audit_filter_task(struct task_struct *tsk, char **key) > rcu_read_lock(); > list_for_each_entry_rcu(e, &audit_filter_list[AUDIT_FILTER_TASK], list) { > if (audit_filter_rules(tsk, &e->rule, NULL, NULL, > - &state, true)) { > + &state)) { > if (state == AUDIT_RECORD_CONTEXT) > *key = kstrdup(e->rule.filterkey, GFP_ATOMIC); > rcu_read_unlock(); > @@ -791,7 +786,7 @@ static enum audit_state audit_filter_syscall(struct task_struct *tsk, > list_for_each_entry_rcu(e, list, list) { > if (audit_in_mask(&e->rule, ctx->major) && > audit_filter_rules(tsk, &e->rule, ctx, NULL, > - &state, false)) { > + &state)) { > rcu_read_unlock(); > ctx->current_state = state; > return state; > @@ -815,7 +810,7 @@ static int audit_filter_inode_name(struct task_struct *tsk, > > list_for_each_entry_rcu(e, list, list) { > if (audit_in_mask(&e->rule, ctx->major) && > - audit_filter_rules(tsk, &e->rule, ctx, n, &state, false)) { > + audit_filter_rules(tsk, &e->rule, ctx, n, &state)) { > ctx->current_state = state; > return 1; > } > -- > 2.24.1 > -- paul moore www.paul-moore.com