atomic_t variables are currently used to implement reference
counters with the following properties:
- counter is initialized to 1 using atomic_set()
- a resource is freed upon counter reaching zero
- once counter reaches zero, its further
increments aren't allowed
- counter schema uses basic atomic operations
(set, inc, inc_not_zero, dec_and_test, etc.)
Such atomic variables should be converted to a newly provided
refcount_t type and API that prevents accidental counter overflows
and underflows. This is important since overflows and underflows
can lead to use-after-free situation and be exploitable.
The variable ring_buffer.aux_refcount is used as pure reference counter.
Convert it to refcount_t and fix up the operations.
Suggested-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reviewed-by: David Windsor <dwindsor@xxxxxxxxx>
Reviewed-by: Hans Liljestrand <ishkamiel@xxxxxxxxx>
Signed-off-by: Elena Reshetova <elena.reshetova@xxxxxxxxx>
---
kernel/events/core.c | 2 +-
kernel/events/internal.h | 2 +-
kernel/events/ring_buffer.c | 6 +++---
3 files changed, 5 insertions(+), 5 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 66d7e18..3848480 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5182,7 +5182,7 @@ static void perf_mmap_close(struct vm_area_struct *vma)
/* this has to be the last one */
rb_free_aux(rb);
- WARN_ON_ONCE(atomic_read(&rb->aux_refcount));
+ WARN_ON_ONCE(refcount_read(&rb->aux_refcount));
mutex_unlock(&event->mmap_mutex);
}
diff --git a/kernel/events/internal.h b/kernel/events/internal.h
index 1cdd9fa..cc5b545 100644
--- a/kernel/events/internal.h
+++ b/kernel/events/internal.h
@@ -48,7 +48,7 @@ struct ring_buffer {
atomic_t aux_mmap_count;
unsigned long aux_mmap_locked;
void (*free_aux)(void *);
- atomic_t aux_refcount;
+ refcount_t aux_refcount;
void **aux_pages;
void *aux_priv;
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 86e1379..08838cd6 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -357,7 +357,7 @@ void *perf_aux_output_begin(struct perf_output_handle *handle,
if (!atomic_read(&rb->aux_mmap_count))
goto err;
- if (!atomic_inc_not_zero(&rb->aux_refcount))
+ if (!refcount_inc_not_zero(&rb->aux_refcount))
goto err;
/*
@@ -655,7 +655,7 @@ int rb_alloc_aux(struct ring_buffer *rb, struct perf_event *event,
* we keep a refcount here to make sure either of the two can
* reference them safely.
*/
- atomic_set(&rb->aux_refcount, 1);
+ refcount_set(&rb->aux_refcount, 1);
rb->aux_overwrite = overwrite;
rb->aux_watermark = watermark;
@@ -674,7 +674,7 @@ int rb_alloc_aux(struct ring_buffer *rb, struct perf_event *event,
void rb_free_aux(struct ring_buffer *rb)
{
- if (atomic_dec_and_test(&rb->aux_refcount))
+ if (refcount_dec_and_test(&rb->aux_refcount))
__rb_free_aux(rb);
}
--
2.7.4
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