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

[Andrew Morton]

Thomas Graf <[EMAIL PROTECTED]> wrote:
>
> * Shailabh Nagar <[EMAIL PROTECTED]> 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
_

-
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