[PATCH v6 1/9] lib/group_cpus: let group_cpu_evenly return number initialized masks

Daniel Wagner
2025-04-24T18:19:48Z

group_cpu_evenly might allocated less groups then the requested:

group_cpu_evenly
__group_cpus_evenly
alloc_nodes_groups
# allocated total groups may be less than numgrps when
# active total CPU number is less then numgrps

In this case, the caller will do an out of bound access because the
caller assumes the masks returned has numgrps.

Return the number of groups created so the caller can limit the access
range accordingly.

Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Daniel Wagner <wagi@kernel.org>
---
block/blk-mq-cpumap.c | 6 +++---
drivers/virtio/virtio_vdpa.c | 9 +++++----
fs/fuse/virtio_fs.c | 6 +++---
include/linux/group_cpus.h | 3 ++-
kernel/irq/affinity.c | 9 +++++----
lib/group_cpus.c | 12 +++++++++---
6 files changed, 27 insertions(+), 18 deletions(-)

diff --git a/block/blk-mq-cpumap.c b/block/blk-mq-cpumap.c
index 444798c5374f48088b661b519f2638bda8556cf2..269161252add756897fce1b65cae5b2e6aebd647 100644
--- a/block/blk-mq-cpumap.c
+++ b/block/blk-mq-cpumap.c
@@ -19,9 +19,9 @@
void blk_mq_map_queues(struct blk_mq_queue_map *qmap)
{
const struct cpumask *masks;
- unsigned int queue, cpu;
+ unsigned int queue, cpu, nr_masks;

- masks = group_cpus_evenly(qmap->nr_queues);
+ masks = group_cpus_evenly(qmap->nr_queues, &nr_masks);
if (!masks) {
for_each_possible_cpu(cpu)
qmap->mq_map[cpu] = qmap->queue_offset;
@@ -29,7 +29,7 @@ void blk_mq_map_queues(struct blk_mq_queue_map *qmap)
}

for (queue = 0; queue < qmap->nr_queues; queue++) {
- for_each_cpu(cpu, &masks[queue])
+ for_each_cpu(cpu, &masks[queue % nr_masks])
qmap->mq_map[cpu] = qmap->queue_offset + queue;
}
kfree(masks);
diff --git a/drivers/virtio/virtio_vdpa.c b/drivers/virtio/virtio_vdpa.c
index 1f60c9d5cb1810a6f208c24bb2ac640d537391a0..a7b297dae4890c9d6002744b90fc133bbedb7b44 100644
--- a/drivers/virtio/virtio_vdpa.c
+++ b/drivers/virtio/virtio_vdpa.c
@@ -329,20 +329,21 @@ create_affinity_masks(unsigned int nvecs, struct irq_affinity *affd)

for (i = 0, usedvecs = 0; i < affd->nr_sets; i++) {
unsigned int this_vecs = affd->set_size[i];
+ unsigned int nr_masks;
int j;
- struct cpumask *result = group_cpus_evenly(this_vecs);
+ struct cpumask *result = group_cpus_evenly(this_vecs, &nr_masks);

if (!result) {
kfree(masks);
return NULL;
}

- for (j = 0; j < this_vecs; j++)
+ for (j = 0; j < nr_masks; j++)
cpumask_copy(&masks[curvec + j], &result[j]);
kfree(result);

- curvec += this_vecs;
- usedvecs += this_vecs;
+ curvec += nr_masks;
+ usedvecs += nr_masks;
}

/* Fill out vectors at the end that don't need affinity */
diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
index 2c7b24cb67adb2cb329ed545f56f04700aca8b81..7ed43b9ea4f3f8b108f1e0d7050c27267b9941c9 100644
--- a/fs/fuse/virtio_fs.c
+++ b/fs/fuse/virtio_fs.c
@@ -862,7 +862,7 @@ static void virtio_fs_requests_done_work(struct work_struct *work)
static void virtio_fs_map_queues(struct virtio_device *vdev, struct virtio_fs *fs)
{
const struct cpumask *mask, *masks;
- unsigned int q, cpu;
+ unsigned int q, cpu, nr_masks;

/* First attempt to map using existing transport layer affinities
* e.g. PCIe MSI-X
@@ -882,7 +882,7 @@ static void virtio_fs_map_queues(struct virtio_device *vdev, struct virtio_fs *f
return;
fallback:
/* Attempt to map evenly in groups over the CPUs */
- masks = group_cpus_evenly(fs->num_request_queues);
+ masks = group_cpus_evenly(fs->num_request_queues, &nr_masks);
/* If even this fails we default to all CPUs use first request queue */
if (!masks) {
for_each_possible_cpu(cpu)
@@ -891,7 +891,7 @@ static void virtio_fs_map_queues(struct virtio_device *vdev, struct virtio_fs *f
}

for (q = 0; q < fs->num_request_queues; q++) {
- for_each_cpu(cpu, &masks[q])
+ for_each_cpu(cpu, &masks[q % nr_masks])
fs->mq_map[cpu] = q + VQ_REQUEST;
}
kfree(masks);
diff --git a/include/linux/group_cpus.h b/include/linux/group_cpus.h
index e42807ec61f6e8cf3787af7daa0d8686edfef0a3..bd5dada6e8606fa6cf8f7babf939e39fd7475c8d 100644
--- a/include/linux/group_cpus.h
+++ b/include/linux/group_cpus.h
@@ -9,6 +9,7 @@
#include <linux/kernel.h>
#include <linux/cpu.h>

-struct cpumask *group_cpus_evenly(unsigned int numgrps);
+struct cpumask *group_cpus_evenly(unsigned int numgrps,
+ unsigned int *nummasks);

#endif
diff --git a/kernel/irq/affinity.c b/kernel/irq/affinity.c
index 44a4eba80315cc098ecfa366ca1d88483641b12a..d2aefab5eb2b929877ced43f48b6268098484bd7 100644
--- a/kernel/irq/affinity.c
+++ b/kernel/irq/affinity.c
@@ -70,20 +70,21 @@ irq_create_affinity_masks(unsigned int nvecs, struct irq_affinity *affd)
*/
for (i = 0, usedvecs = 0; i < affd->nr_sets; i++) {
unsigned int this_vecs = affd->set_size[i];
+ unsigned int nr_masks;
int j;
- struct cpumask *result = group_cpus_evenly(this_vecs);
+ struct cpumask *result = group_cpus_evenly(this_vecs, &nr_masks);

if (!result) {
kfree(masks);
return NULL;
}

- for (j = 0; j < this_vecs; j++)
+ for (j = 0; j < nr_masks; j++)
cpumask_copy(&masks[curvec + j].mask, &result[j]);
kfree(result);

- curvec += this_vecs;
- usedvecs += this_vecs;
+ curvec += nr_masks;
+ usedvecs += nr_masks;
}

/* Fill out vectors at the end that don't need affinity */
diff --git a/lib/group_cpus.c b/lib/group_cpus.c
index ee272c4cefcc13907ce9f211f479615d2e3c9154..016c6578a07616959470b47121459a16a1bc99e5 100644
--- a/lib/group_cpus.c
+++ b/lib/group_cpus.c
@@ -332,9 +332,11 @@ static int __group_cpus_evenly(unsigned int startgrp, unsigned int numgrps,
/**
* group_cpus_evenly - Group all CPUs evenly per NUMA/CPU locality
* @numgrps: number of groups
+ * @nummasks: number of initialized cpumasks
*
* Return: cpumask array if successful, NULL otherwise. And each element
- * includes CPUs assigned to this group
+ * includes CPUs assigned to this group. nummasks contains the number
+ * of initialized masks which can be less than numgrps.
*
* Try to put close CPUs from viewpoint of CPU and NUMA locality into
* same group, and run two-stage grouping:
@@ -344,7 +346,8 @@ static int __group_cpus_evenly(unsigned int startgrp, unsigned int numgrps,
* We guarantee in the resulted grouping that all CPUs are covered, and
* no same CPU is assigned to multiple groups
*/
-struct cpumask *group_cpus_evenly(unsigned int numgrps)
+struct cpumask *group_cpus_evenly(unsigned int numgrps,
+ unsigned int *nummasks)
{
unsigned int curgrp = 0, nr_present = 0, nr_others = 0;
cpumask_var_t *node_to_cpumask;
@@ -421,10 +424,12 @@ struct cpumask *group_cpus_evenly(unsigned int numgrps)
kfree(masks);
return NULL;
}
+ *nummasks = nr_present + nr_others;
return masks;
}
#else /* CONFIG_SMP */
-struct cpumask *group_cpus_evenly(unsigned int numgrps)
+struct cpumask *group_cpus_evenly(unsigned int numgrps,
+ unsigned int *nummasks)
{
struct cpumask *masks = kcalloc(numgrps, sizeof(*masks), GFP_KERNEL);

@@ -433,6 +438,7 @@ struct cpumask *group_cpus_evenly(unsigned int numgrps)

/* assign all CPUs(cpu 0) to the 1st group only */
cpumask_copy(&masks[0], cpu_possible_mask);
+ *nummasks = 1;
return masks;
}
#endif /* CONFIG_SMP */

--
2.49.0