Re: [PATCH RFC v2 4/4] mm/mempolicy: add nodes_empty check in SYSC_migrate_pages
From: Vlastimil Babka <hidden>
Date: 2017-10-31 09:46:42
Also in:
linux-api, lkml
+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".
quoted hunk ↗ jump to hunk
Signed-off-by: Yisheng Xie <redacted> --- 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;
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