[PATCH AUTOSEL 4.19 06/13] lib: cpu_rmap: Avoid use after free on rmap->obj array entries

[Sasha Levin]

From: Eli Cohen <elic@xxxxxxxxxx>

[ Upstream commit 4e0473f1060aa49621d40a113afde24818101d37 ]

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().

The current code does not suffer from this since there are no cases
where irq_set_affinity_notifier(irq, NULL) (note the NULL passed for the
notify arg) is called, followed by a call to free_irq_cpu_rmap() so we
don't hit and issue. Subsequent patches in this series excersize this
flow, hence the required fix.

Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Eli Cohen <elic@xxxxxxxxxx>
Signed-off-by: Saeed Mahameed <saeedm@xxxxxxxxxx>
Reviewed-by: Jacob Keller <jacob.e.keller@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 lib/cpu_rmap.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/lib/cpu_rmap.c b/lib/cpu_rmap.c
index f610b2a10b3ed..f52389054a24f 100644
--- a/lib/cpu_rmap.c
+++ b/lib/cpu_rmap.c
@@ -235,7 +235,8 @@ 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);
@@ -271,6 +272,7 @@ 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);
 }
 
@@ -300,6 +302,7 @@ int irq_cpu_rmap_add(struct cpu_rmap *rmap, int irq)
 	rc = irq_set_affinity_notifier(irq, &glue->notify);
 	if (rc) {
 		cpu_rmap_put(glue->rmap);
+		rmap->obj[glue->index] = NULL;
 		kfree(glue);
 	}
 	return rc;
-- 
2.39.2