Re: [PATCH v4 3/3] mm/mempolicy: add nodes_empty check in SYSC_migrate_pages
From: Vlastimil Babka <hidden>
Date: 2017-12-01 15:20:12
Also in:
linux-mm, lkml
On 12/01/2017 10:55 AM, Yisheng Xie wrote:
As in 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. Meanwhile,this patch also remove the check of EPERM on CAP_SYS_NICE. The caller of migrate_pages should be able to migrate the target process pages anywhere the caller can allocate memory, if the caller can access the mm_struct. Signed-off-by: Yisheng Xie <redacted> Cc: Andi Kleen <redacted> Cc: Chris Salls <redacted> Cc: Christopher Lameter <redacted> Cc: David Rientjes <rientjes@google.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Naoya Horiguchi <redacted> Cc: Tan Xiaojun <redacted> Cc: Vlastimil Babka <redacted> --- v3: * check whether node is empty after AND current task node, and then nodes which have memory v4: * remove the check of EPERM on CAP_SYS_NICE. Hi Vlastimil and Christopher, Could you please help to review this version?
Hi, I think we should stay with v3 after all. What I missed when reviewing it, is that the EPERM check is for cpuset_mems_allowed(task) and in v3 you add EINVAL check for cpuset_mems_allowed(current), which may not be the same, and the intention of CAP_SYS_NICE is not whether we can bypass our own cpuset, but whether we can bypass the target task's cpuset. Sorry for the confusion.
quoted hunk ↗ jump to hunk
Thanks Yisheng Xie mm/mempolicy.c | 13 +++++-------- 1 file changed, 5 insertions(+), 8 deletions(-)diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 65df28d..4da74b6 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c@@ -1426,17 +1426,14 @@ static int copy_nodes_to_user(unsigned long __user *mask, unsigned long maxnode, } rcu_read_unlock(); - 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; + task_nodes = cpuset_mems_allowed(current); + nodes_and(*new, *new, task_nodes); + if (nodes_empty(*new)) goto out_put; - } - if (!nodes_subset(*new, node_states[N_MEMORY])) { - err = -EINVAL; + nodes_and(*new, *new, node_states[N_MEMORY]); + if (nodes_empty(*new)) goto out_put; - } err = security_task_movememory(task); if (err)