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    Subject[PATCH v9 11/20] sched: Split the guts of sched_setaffinity() into a helper function
    Date
    In preparation for replaying user affinity requests using a saved mask,
    split sched_setaffinity() up so that the initial task lookup and
    security checks are only performed when the request is coming directly
    from userspace.

    Reviewed-by: Valentin Schneider <Valentin.Schneider@arm.com>
    Signed-off-by: Will Deacon <will@kernel.org>
    ---
    kernel/sched/core.c | 105 ++++++++++++++++++++++++--------------------
    1 file changed, 57 insertions(+), 48 deletions(-)

    diff --git a/kernel/sched/core.c b/kernel/sched/core.c
    index f6ea3d7a07f2..d151446d5987 100644
    --- a/kernel/sched/core.c
    +++ b/kernel/sched/core.c
    @@ -6787,53 +6787,22 @@ SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr,
    return retval;
    }

    -long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
    +static int
    +__sched_setaffinity(struct task_struct *p, const struct cpumask *mask)
    {
    - cpumask_var_t cpus_allowed, new_mask;
    - struct task_struct *p;
    int retval;
    + cpumask_var_t cpus_allowed, new_mask;

    - rcu_read_lock();
    -
    - p = find_process_by_pid(pid);
    - if (!p) {
    - rcu_read_unlock();
    - return -ESRCH;
    - }
    -
    - /* Prevent p going away */
    - get_task_struct(p);
    - rcu_read_unlock();
    + if (!alloc_cpumask_var(&cpus_allowed, GFP_KERNEL))
    + return -ENOMEM;

    - if (p->flags & PF_NO_SETAFFINITY) {
    - retval = -EINVAL;
    - goto out_put_task;
    - }
    - if (!alloc_cpumask_var(&cpus_allowed, GFP_KERNEL)) {
    - retval = -ENOMEM;
    - goto out_put_task;
    - }
    if (!alloc_cpumask_var(&new_mask, GFP_KERNEL)) {
    retval = -ENOMEM;
    goto out_free_cpus_allowed;
    }
    - retval = -EPERM;
    - if (!check_same_owner(p)) {
    - rcu_read_lock();
    - if (!ns_capable(__task_cred(p)->user_ns, CAP_SYS_NICE)) {
    - rcu_read_unlock();
    - goto out_free_new_mask;
    - }
    - rcu_read_unlock();
    - }
    -
    - retval = security_task_setscheduler(p);
    - if (retval)
    - goto out_free_new_mask;
    -

    cpuset_cpus_allowed(p, cpus_allowed);
    - cpumask_and(new_mask, in_mask, cpus_allowed);
    + cpumask_and(new_mask, mask, cpus_allowed);

    /*
    * Since bandwidth control happens on root_domain basis,
    @@ -6854,23 +6823,63 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
    #endif
    again:
    retval = __set_cpus_allowed_ptr(p, new_mask, SCA_CHECK);
    + if (retval)
    + goto out_free_new_mask;

    - if (!retval) {
    - cpuset_cpus_allowed(p, cpus_allowed);
    - if (!cpumask_subset(new_mask, cpus_allowed)) {
    - /*
    - * We must have raced with a concurrent cpuset
    - * update. Just reset the cpus_allowed to the
    - * cpuset's cpus_allowed
    - */
    - cpumask_copy(new_mask, cpus_allowed);
    - goto again;
    - }
    + cpuset_cpus_allowed(p, cpus_allowed);
    + if (!cpumask_subset(new_mask, cpus_allowed)) {
    + /*
    + * We must have raced with a concurrent cpuset update.
    + * Just reset the cpumask to the cpuset's cpus_allowed.
    + */
    + cpumask_copy(new_mask, cpus_allowed);
    + goto again;
    }
    +
    out_free_new_mask:
    free_cpumask_var(new_mask);
    out_free_cpus_allowed:
    free_cpumask_var(cpus_allowed);
    + return retval;
    +}
    +
    +long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
    +{
    + struct task_struct *p;
    + int retval;
    +
    + rcu_read_lock();
    +
    + p = find_process_by_pid(pid);
    + if (!p) {
    + rcu_read_unlock();
    + return -ESRCH;
    + }
    +
    + /* Prevent p going away */
    + get_task_struct(p);
    + rcu_read_unlock();
    +
    + if (p->flags & PF_NO_SETAFFINITY) {
    + retval = -EINVAL;
    + goto out_put_task;
    + }
    +
    + if (!check_same_owner(p)) {
    + rcu_read_lock();
    + if (!ns_capable(__task_cred(p)->user_ns, CAP_SYS_NICE)) {
    + rcu_read_unlock();
    + retval = -EPERM;
    + goto out_put_task;
    + }
    + rcu_read_unlock();
    + }
    +
    + retval = security_task_setscheduler(p);
    + if (retval)
    + goto out_put_task;
    +
    + retval = __sched_setaffinity(p, in_mask);
    out_put_task:
    put_task_struct(p);
    return retval;
    --
    2.32.0.rc1.229.g3e70b5a671-goog
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