rlimits: redo do_setrlimit to more generic do_prlimit

It now allows also reading of limits. I.e. all read and writes will
later use this function.

It takes two parameters, new and old limits which can be both NULL.
If new is non-NULL, the value in it is set to rlimits.
If old is non-NULL, current rlimits are stored there.
If both are non-NULL, old are stored prior to setting the new ones,
atomically.
(Similar to sigaction.)
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

include/linux/resource.h

@@ -80,8 +80,8 @@ struct rlimit64 {
 struct task_struct;
 
 int getrusage(struct task_struct *p, int who, struct rusage __user *ru);
-int do_setrlimit(struct task_struct *tsk, unsigned int resource,
-		struct rlimit *new_rlim);
+int do_prlimit(struct task_struct *tsk, unsigned int resource,
+		struct rlimit *new_rlim, struct rlimit *old_rlim);
 
 #endif /* __KERNEL__ */
 

kernel/sys.c

@@ -1273,18 +1273,21 @@ SYSCALL_DEFINE2(old_getrlimit, unsigned int, resource,
 #endif
 
 /* make sure you are allowed to change @tsk limits before calling this */
-int do_setrlimit(struct task_struct *tsk, unsigned int resource,
-		struct rlimit *new_rlim)
+int do_prlimit(struct task_struct *tsk, unsigned int resource,
+		struct rlimit *new_rlim, struct rlimit *old_rlim)
 {
-	struct rlimit *old_rlim;
+	struct rlimit *rlim;
 	int retval = 0;
 
 	if (resource >= RLIM_NLIMITS)
 		return -EINVAL;
-	if (new_rlim->rlim_cur > new_rlim->rlim_max)
-		return -EINVAL;
-	if (resource == RLIMIT_NOFILE && new_rlim->rlim_max > sysctl_nr_open)
-		return -EPERM;
+	if (new_rlim) {
+		if (new_rlim->rlim_cur > new_rlim->rlim_max)
+			return -EINVAL;
+		if (resource == RLIMIT_NOFILE &&
+				new_rlim->rlim_max > sysctl_nr_open)
+			return -EPERM;
+	}
 
 	/* protect tsk->signal and tsk->sighand from disappearing */
 	read_lock(&tasklist_lock);
@@ -1293,42 +1296,42 @@ int do_setrlimit(struct task_struct *tsk, unsigned int resource,
 		goto out;
 	}
 
-	old_rlim = tsk->signal->rlim + resource;
+	rlim = tsk->signal->rlim + resource;
 	task_lock(tsk->group_leader);
-	if (new_rlim->rlim_max > old_rlim->rlim_max &&
-			!capable(CAP_SYS_RESOURCE))
-		retval = -EPERM;
-	if (!retval)
-		retval = security_task_setrlimit(tsk->group_leader, resource,
-				new_rlim);
-
-	if (resource == RLIMIT_CPU && new_rlim->rlim_cur == 0) {
-		/*
-		 * The caller is asking for an immediate RLIMIT_CPU
-		 * expiry.  But we use the zero value to mean "it was
-		 * never set".  So let's cheat and make it one second
-		 * instead
-		 */
-		new_rlim->rlim_cur = 1;
+	if (new_rlim) {
+		if (new_rlim->rlim_max > rlim->rlim_max &&
+				!capable(CAP_SYS_RESOURCE))
+			retval = -EPERM;
+		if (!retval)
+			retval = security_task_setrlimit(tsk->group_leader,
+					resource, new_rlim);
+		if (resource == RLIMIT_CPU && new_rlim->rlim_cur == 0) {
+			/*
+			 * The caller is asking for an immediate RLIMIT_CPU
+			 * expiry.  But we use the zero value to mean "it was
+			 * never set".  So let's cheat and make it one second
+			 * instead
+			 */
+			new_rlim->rlim_cur = 1;
+		}
+	}
+	if (!retval) {
+		if (old_rlim)
+			*old_rlim = *rlim;
+		if (new_rlim)
+			*rlim = *new_rlim;
 	}
-
-	if (!retval)
-		*old_rlim = *new_rlim;
 	task_unlock(tsk->group_leader);
 
-	if (retval || resource != RLIMIT_CPU)
-		goto out;
-
 	/*
 	 * RLIMIT_CPU handling.   Note that the kernel fails to return an error
 	 * code if it rejected the user's attempt to set RLIMIT_CPU.  This is a
 	 * very long-standing error, and fixing it now risks breakage of
 	 * applications, so we live with it
 	 */
-	if (new_rlim->rlim_cur == RLIM_INFINITY)
-		goto out;
-
-	update_rlimit_cpu(tsk, new_rlim->rlim_cur);
+	 if (!retval && new_rlim && resource == RLIMIT_CPU &&
+			 new_rlim->rlim_cur != RLIM_INFINITY)
+		update_rlimit_cpu(tsk, new_rlim->rlim_cur);
 out:
 	read_unlock(&tasklist_lock);
 	return retval;
@@ -1340,7 +1343,7 @@ SYSCALL_DEFINE2(setrlimit, unsigned int, resource, struct rlimit __user *, rlim)
 
 	if (copy_from_user(&new_rlim, rlim, sizeof(*rlim)))
 		return -EFAULT;
-	return do_setrlimit(current, resource, &new_rlim);
+	return do_prlimit(current, resource, &new_rlim, NULL);
 }
 
 /*