[PATCH 1/1] mm: cma: check the max limit for cma allocation

[Shiraz Hashim]

CMA allocation request size is represented by size_t that
gets truncated when same is passed as int to
bitmap_find_next_zero_area_off.

We observe that during fuzz testing when cma allocation
request is too high, bitmap_find_next_zero_area_off still
returns success due to the truncation. This leads to
kernel crash, as subsequent code assumes that requested
memory is available.

Fail cma allocation in case the request breaches the
corresponding cma region size.

Signed-off-by: Shiraz Hashim <shashim@xxxxxxxxxxxxxx>
---
 mm/cma.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/cma.c b/mm/cma.c
index 384c2cb..c960459 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -385,6 +385,9 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align)
 	bitmap_maxno = cma_bitmap_maxno(cma);
 	bitmap_count = cma_bitmap_pages_to_bits(cma, count);
 
+	if (bitmap_count > bitmap_maxno)
+		return NULL;
+
 	for (;;) {
 		mutex_lock(&cma->lock);
 		bitmap_no = bitmap_find_next_zero_area_off(cma->bitmap,
-- 
Shiraz Hashim

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