linux-kernel - [PATCH] lib: cpu_rmap: Avoid use after free on rmap->obj array entries

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Date:   Wed, 8 Feb 2023 13:45:15 +0200
From:   Eli Cohen <elic@...dia.com>
To:     <linux-kernel@...r.kernel.org>, <bhutchings@...arflare.com>
CC:     Eli Cohen <elic@...dia.com>
Subject: [PATCH] lib: cpu_rmap: Avoid use after free on rmap->obj array entries

When calling irq_set_affinity_notifier() with NULL at the notify
argument, it will cause freeing of the glue pointer in the
corresponding array entry but will leave the pointer in the array. A
subsequent call to free_irq_cpu_rmap() will try to free this entry again
leading to possible use after free.

Fix that by setting NULL to the array entry and checking that we have
non-zero at the array entry when iterating over the array in
free_irq_cpu_rmap().

Fixes: c39649c331c7 ("lib: cpu_rmap: CPU affinity reverse-mapping")
Signed-off-by: Eli Cohen <elic@...dia.com>
---
 lib/cpu_rmap.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lib/cpu_rmap.c b/lib/cpu_rmap.c
index f08d9c56f712..c2ce2200a202 100644
--- a/lib/cpu_rmap.c
+++ b/lib/cpu_rmap.c
@@ -232,7 +232,8 @@ void free_irq_cpu_rmap(struct cpu_rmap *rmap)
 
 	for (index = 0; index < rmap->used; index++) {
 		glue = rmap->obj[index];
-		irq_set_affinity_notifier(glue->notify.irq, NULL);
+		if (glue)
+			irq_set_affinity_notifier(glue->notify.irq, NULL);
 	}
 
 	cpu_rmap_put(rmap);
@@ -268,6 +269,7 @@ static void irq_cpu_rmap_release(struct kref *ref)
 		container_of(ref, struct irq_glue, notify.kref);
 
 	cpu_rmap_put(glue->rmap);
+	glue->rmap->obj[glue->index] = NULL;
 	kfree(glue);
 }
 
-- 
2.38.1