Nouveau - Mar 2024 - [PATCH] nouveau/dmem: handle kcalloc() allocation failure

The kcalloc() in nouveau_dmem_evict_chunk() will return null if
the physical memory has run out. As a result, if we dereference
src_pfns, dst_pfns or dma_addrs, the null pointer dereference bugs
will happen.

This patch uses stack variables to replace the kcalloc().

Fixes: 249881232e14 ("nouveau/dmem: evict device private memory during
release")
Signed-off-by: Duoming Zhou <duoming at zju.edu.cn>
---
 drivers/gpu/drm/nouveau/nouveau_dmem.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c
b/drivers/gpu/drm/nouveau/nouveau_dmem.c
index 12feecf71e7..9a578262c6d 100644
--- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
+++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
@@ -374,13 +374,13 @@ static void
 nouveau_dmem_evict_chunk(struct nouveau_dmem_chunk *chunk)
 {
 	unsigned long i, npages = range_len(&chunk->pagemap.range) >>
PAGE_SHIFT;
-	unsigned long *src_pfns, *dst_pfns;
-	dma_addr_t *dma_addrs;
+	unsigned long src_pfns[npages], dst_pfns[npages];
+	dma_addr_t dma_addrs[npages];
 	struct nouveau_fence *fence;
 
-	src_pfns = kcalloc(npages, sizeof(*src_pfns), GFP_KERNEL);
-	dst_pfns = kcalloc(npages, sizeof(*dst_pfns), GFP_KERNEL);
-	dma_addrs = kcalloc(npages, sizeof(*dma_addrs), GFP_KERNEL);
+	memset(src_pfns, 0, npages);
+	memset(dst_pfns, 0, npages);
+	memset(dma_addrs, 0, npages);
 
 	migrate_device_range(src_pfns, chunk->pagemap.range.start >>
PAGE_SHIFT,
 			npages);
@@ -406,11 +406,8 @@ nouveau_dmem_evict_chunk(struct nouveau_dmem_chunk *chunk)
 	migrate_device_pages(src_pfns, dst_pfns, npages);
 	nouveau_dmem_fence_done(&fence);
 	migrate_device_finalize(src_pfns, dst_pfns, npages);
-	kfree(src_pfns);
-	kfree(dst_pfns);
 	for (i = 0; i < npages; i++)
 		dma_unmap_page(chunk->drm->dev->dev, dma_addrs[i], PAGE_SIZE,
DMA_BIDIRECTIONAL);
-	kfree(dma_addrs);
 }
 
 void
-- 
2.17.1

On Sun, Mar 3, 2024 at 4:46?AM Duoming Zhou <duoming at zju.edu.cn>
wrote:
>
> The kcalloc() in nouveau_dmem_evict_chunk() will return null if
> the physical memory has run out. As a result, if we dereference
> src_pfns, dst_pfns or dma_addrs, the null pointer dereference bugs
> will happen.
>
> This patch uses stack variables to replace the kcalloc().
Won't this blow the stack?  And why not just test the return value of
kcalloc?