Re: [PATCH] per-task delay accounting taskstats interface: control exit data through cpumasks]

[Andrew Morton <akpm@osdl.org>]

Thomas Graf <tgraf@suug.ch> wrote:
>
> * Shailabh Nagar <nagar@watson.ibm.com> 2006-07-06 07:37
> > @@ -37,9 +45,26 @@ static struct nla_policy taskstats_cmd_g
> >  __read_mostly = {
> >  	[TASKSTATS_CMD_ATTR_PID]  = { .type = NLA_U32 },
> >  	[TASKSTATS_CMD_ATTR_TGID] = { .type = NLA_U32 },
> > +	[TASKSTATS_CMD_ATTR_REGISTER_CPUMASK] = { .type = NLA_STRING },
> > +	[TASKSTATS_CMD_ATTR_DEREGISTER_CPUMASK] = { .type = NLA_STRING },};
> 
> > +		na = info->attrs[TASKSTATS_CMD_ATTR_REGISTER_CPUMASK];
> > +		if (nla_len(na) > TASKSTATS_CPUMASK_MAXLEN)
> > +			return -E2BIG;
> > +		rc = cpulist_parse((char *)nla_data(na), mask);
> 
> This isn't safe, the data in the attribute is not guaranteed to be
> NUL terminated. Still it's probably me to blame for not making
> this more obvious in the API.
> 

Thanks, that was an unpleasant bug.

> I've attached a patch below extending the API to make it easier
> for interfaces using NUL termianted strings,

In the interests of keeping this work decoupled from netlink enhancements
I'd propose the below.  Is it bad to modify the data at nla_data()?


--- a/kernel/taskstats.c~per-task-delay-accounting-taskstats-interface-control-exit-data-through-cpumasks-fix
+++ a/kernel/taskstats.c
@@ -299,6 +299,23 @@ cleanup:
 	return 0;
 }
 
+static int parse(struct nlattr *na, cpumask_t *mask)
+{
+	char *data;
+	int len;
+
+	if (na == NULL)
+		return 1;
+	len = nla_len(na);
+	if (len > TASKSTATS_CPUMASK_MAXLEN)
+		return -E2BIG;
+	if (len < 1)
+		return -EINVAL;
+	data = nla_data(na);
+	data[len - 1] = '\0';
+	return cpulist_parse(data, *mask);
+}
+
 static int taskstats_user_cmd(struct sk_buff *skb, struct genl_info *info)
 {
 	int rc = 0;
@@ -309,27 +326,17 @@ static int taskstats_user_cmd(struct sk_
 	struct nlattr *na;
 	cpumask_t mask;
 
-	if (info->attrs[TASKSTATS_CMD_ATTR_REGISTER_CPUMASK]) {
-		na = info->attrs[TASKSTATS_CMD_ATTR_REGISTER_CPUMASK];
-		if (nla_len(na) > TASKSTATS_CPUMASK_MAXLEN)
-			return -E2BIG;
-		rc = cpulist_parse((char *)nla_data(na), mask);
-		if (rc)
-			return rc;
-		rc = add_del_listener(info->snd_pid, &mask, REGISTER);
+	rc = parse(info->attrs[TASKSTATS_CMD_ATTR_REGISTER_CPUMASK], &mask);
+	if (rc < 0)
 		return rc;
-	}
+	if (rc == 0)
+		return add_del_listener(info->snd_pid, &mask, REGISTER);
 
-	if (info->attrs[TASKSTATS_CMD_ATTR_DEREGISTER_CPUMASK]) {
-		na = info->attrs[TASKSTATS_CMD_ATTR_DEREGISTER_CPUMASK];
-		if (nla_len(na) > TASKSTATS_CPUMASK_MAXLEN)
-			return -E2BIG;
-		rc = cpulist_parse((char *)nla_data(na), mask);
-		if (rc)
-			return rc;
-		rc = add_del_listener(info->snd_pid, &mask, DEREGISTER);
+	rc = parse(info->attrs[TASKSTATS_CMD_ATTR_DEREGISTER_CPUMASK], &mask);
+	if (rc < 0)
 		return rc;
-	}
+	if (rc == 0)
+		return add_del_listener(info->snd_pid, &mask, DEREGISTER);
 
 	/*
 	 * Size includes space for nested attributes
_