Re: [PATCH v3 3/3] mm/mempolicy: add nodes_empty check in SYSC_migrate_pages
From: Vlastimil Babka <hidden>
Date: 2017-11-27 17:27:18
Also in:
linux-mm, lkml
On 11/17/2017 02:37 AM, Yisheng Xie wrote:
quoted hunk ↗ jump to hunk
As manpage of migrate_pages, the errno should be set to EINVAL when 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. However, when test by 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. As the new_nodes is empty, we should expect EINVAL as documented. To fix the case like above, this patch check whether target nodes AND current task_nodes is empty, and then check whether AND node_states[N_MEMORY] is empty. Signed-off-by: Yisheng Xie <redacted> --- mm/mempolicy.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 65df28d..f604b22 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c@@ -1433,10 +1433,14 @@ static int copy_nodes_to_user(unsigned long __user *mask, unsigned long maxnode, goto out_put; }
Let me add the whole preceding that ends on the lines above:
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;
+ task_nodes = cpuset_mems_allowed(current);
+ nodes_and(*new, *new, task_nodes);
+ if (nodes_empty(*new))
+ goto out_put;So if we have CAP_SYS_NICE, we pass (or rather skip) the EPERM check above, but the current cpuset restriction still applies regardless. This doesn't make sense to me? If I get Christoph right in the v2 discussion, then CAP_SYS_NICE should not allow current cpuset escape. In that case, we should remove the CAP_SYS_NICE check from the EPERM check? Also should it be a subset check, or a non-empty-intersection check? Note there's still a danger that we are breaking existing code so this will have to be reverted in any case...
+ + nodes_and(*new, *new, node_states[N_MEMORY]); + if (nodes_empty(*new)) goto out_put; - } err = security_task_movememory(task); if (err)