+CC Andi and Christoph
On 10/27/2017 12:14 PM, Yisheng Xie wrote:
> As manpage of migrate_pages, the errno should be set to EINVAL when none
> of the specified nodes contain memory. However, when new_nodes is null,
> i.e. the specified nodes also do not have memory, as the following case:
>
> new_nodes = 0;
> old_nodes = 0xf;
> ret = migrate_pages(pid, old_nodes, new_nodes, MAX);
>
> The ret will be 0 and no errno is set.
>
> This patch is to add nodes_empty check to fix above case.
Hmm, I think we have a bigger problem than "empty set is a subset of
anything" here.
The existing checks are:
task_nodes = cpuset_mems_allowed(task);
/* Is the user allowed to access the target nodes? */
if (!nodes_subset(*new, task_nodes) && !capable(CAP_SYS_NICE)) {
err = -EPERM;
goto out_put;
}
if (!nodes_subset(*new, node_states[N_MEMORY])) {
err = -EINVAL;
goto out_put;
}
And manpage says:
EINVAL The value specified by maxnode exceeds a kernel-imposed
limit. Or, old_nodes or new_nodes specifies one or more node IDs that
are greater than the maximum supported node
ID. *Or, none of the node IDs specified by new_nodes are
on-line and allowed by the process's current cpuset context, or none of
the specified nodes contain memory.*
EPERM Insufficient privilege (CAP_SYS_NICE) to move pages of the
process specified by pid, or insufficient privilege (CAP_SYS_NICE) to
access the specified target nodes.
- it says "none ... are allowed", but checking for subset means we check
if "all ... are allowed". Shouldn't we be checking for a non-empty
intersection?
- there doesn't seem to be any EINVAL check for "process's current
cpuset context", there's just an EPERM check for "target process's
cpuset context".
>
> Signed-off-by: Yisheng Xie <[email protected]>
> ---
> mm/mempolicy.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 8798ecb..58352cc 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -1402,6 +1402,11 @@ static int copy_nodes_to_user(unsigned long __user
> *mask, unsigned long maxnode,
> if (err)
> goto out;
>
> + if (nodes_empty(*new)) {
> + err = -EINVAL;
> + goto out;
> + }
> +
> /* Find the mm_struct */
> rcu_read_lock();
> task = pid ? find_task_by_vpid(pid) : current;
>
