[PATCH] mm/cma_debug: fix invalid accesses for inactive CMA areas

[Muchun Song]

cma_activate_area() can fail after allocating range bitmaps. Its cleanup
path frees those bitmaps, but only clears cma->count and
cma->available_count. It leaves cma->nranges and each range's count in
place, so cma_debugfs_init() can still register debugfs files for an area
that never activated successfully.

That exposes two problems. Reading the bitmap file can make debugfs walk a
freed range bitmap and trigger an invalid memory access. Reading maxchunk
can also take cma->lock even though that lock is initialized only on the
successful activation path.

Fix this by creating debugfs entries only for CMA areas that reached
CMA_ACTIVATED.

Fixes: c009da4258f9 ("mm, cma: support multiple contiguous ranges, if requested")
Fixes: 2e32b947606d ("mm: cma: add functions to get region pages counters")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---
 mm/cma_debug.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/cma_debug.c b/mm/cma_debug.c
index 5ae38f5abbcc..523ba4a0f9f7 100644
--- a/mm/cma_debug.c
+++ b/mm/cma_debug.c
@@ -205,7 +205,8 @@ static int __init cma_debugfs_init(void)
 	cma_debugfs_root = debugfs_create_dir("cma", NULL);
 
 	for (i = 0; i < cma_area_count; i++)
-		cma_debugfs_add_one(&cma_areas[i], cma_debugfs_root);
+		if (test_bit(CMA_ACTIVATED, &cma_areas[i].flags))
+			cma_debugfs_add_one(&cma_areas[i], cma_debugfs_root);
 
 	return 0;
 }

base-commit: e98d21c170b01ddef366f023bbfcf6b31509fa83
-- 
2.54.0