Re: [PATCH 2.6.13-rc6 1/2] New Syscall: get rlimits of any process

From: Andrew Morton (akpm_at_osdl.org)
Date: 08/21/05

  • Next message: Robert Han***: "Re: sched_yield() makes OpenLDAP slow" 
    Date:	Sat, 20 Aug 2005 18:11:02 -0700
To: e8607062@student.tuwien.ac.at

    Wieland Gmeiner <e8607062@student.tuwien.ac.at> wrote:
    >
    > +asmlinkage long sys_getprlimit(pid_t pid, unsigned int resource, struct rlimit __user *rlim)
    > +{
    > + struct rlimit value;
    > + task_t *p;
    > + int retval = -EINVAL;
    > +
    > + if (resource >= RLIM_NLIMITS)
    > + goto out_nounlock;
    > +
    > + if (pid < 0)
    > + goto out_nounlock;
    > +
    > + retval = -ESRCH;
    > + if (pid == 0) {
    > + p = current;
    > + } else {
    > + read_lock(&tasklist_lock);
    > + p = find_task_by_pid(pid);
    > + }
    > + if (p) {
    > + retval = -EPERM;
    > + if ((current->euid ^ p->suid) && (current->euid ^ p->uid) &&
    > + (current->uid ^ p->suid) && (current->uid ^ p->uid) &&
    > + !capable(CAP_SYS_RESOURCE))
    > + goto out_unlock;
    > +
    > + task_lock(p->group_leader);
    > + value = p->signal->rlim[resource];
    > + task_unlock(p->group_leader);

    There isn't much point in taking task_lock() here. The value can change
    after the lock has been dropped anyway.

    > + retval = copy_to_user(rlim, &value, sizeof(*rlim)) ? -EFAULT : 0;

    It's not legal to perform copy_*_user() (which sleeps) inside read_lock(),
    write_lock(), spin_lock(), preempt_diable() or, really,
    local_irq_disable().

    > + }
    > + if (pid == 0)
    > + goto out_nounlock;
    > +
    > +out_unlock:
    > + read_unlock(&tasklist_lock);
    -
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