[PATCH] Extending getrusage

["Claudio Scordino" <cloud.of.andor@gmail.com>]

For the people who missed the beginning of the discussion, the
following patch is an extension of the existing getrusage syscall()
and it applies to the 2.6.16.9 kernel.

It allows a task to read usage information about another task. The argument
who can be equal to RUSAGE_SELF, to RUSAGE_CHILDREN or to a valid pid.

The permissions are checked through security_ptrace() as suggested by Andy.

Any other comment ?

Thanks,

           Claudio


Signed-off-by: Claudio Scordino <cloud.of.andor@gmail.com>
--- sys.old.c	2006-04-19 02:10:14.000000000 -0400
+++ sys.c	2006-04-20 10:53:16.000000000 -0400
@@ -1765,11 +1765,30 @@ int getrusage(struct task_struct *p, int
 	return copy_to_user(ru, &r, sizeof(r)) ? -EFAULT : 0;
 }

+/* who can be RUSAGE_SELF, RUSAGE_CHILDREN or a valid pid */
 asmlinkage long sys_getrusage(int who, struct rusage __user *ru)
 {
-	if (who != RUSAGE_SELF && who != RUSAGE_CHILDREN)
-		return -EINVAL;
-	return getrusage(current, who, ru);
+	struct rusage r;
+	struct task_struct* tsk = current;
+	read_lock(&tasklist_lock);
+	if ((who != RUSAGE_SELF) && (who != RUSAGE_CHILDREN)) {
+		if (who <= 0)
+			goto bad;
+		tsk = find_task_by_pid(who);
+		if (tsk == NULL)
+			goto bad;
+		if ((tsk != current) && security_ptrace(current, tsk))
+			goto bad;
+		/* current can get info about tsk */
+		who = RUSAGE_SELF;
+	}
+	k_getrusage(tsk, who, &r);
+	read_unlock(&tasklist_lock);
+	return copy_to_user(ru, &r, sizeof(r)) ? -EFAULT : 0;
+
+bad:
+	read_unlock(&tasklist_lock);
+	return tsk ? -EPERM : -EINVAL;
 }

 asmlinkage long sys_umask(int mask)