Re: [PATCH 13/21] dmaengine: stm32-mdma: Annotate struct stm32_mdma_desc with __counted_by

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On 8/17/23 17:58, Kees Cook wrote:
Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
(for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family

As found with Coccinelle[1], add __counted_by for struct stm32_mdma_desc.
Additionally, since the element count member must be set before accessing
the annotated flexible array member, move its initialization earlier.


Cc: Vinod Koul <vkoul@xxxxxxxxxx>
Cc: Maxime Coquelin <mcoquelin.stm32@xxxxxxxxx>
Cc: Alexandre Torgue <alexandre.torgue@xxxxxxxxxxx>
Cc: dmaengine@xxxxxxxxxxxxxxx
Cc: linux-stm32@xxxxxxxxxxxxxxxxxxxxxxxxxxxx
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>

Reviewed-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>


  drivers/dma/stm32-mdma.c | 5 ++---
  1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/dma/stm32-mdma.c b/drivers/dma/stm32-mdma.c
index 0de234022c6d..926d6ecf1274 100644
--- a/drivers/dma/stm32-mdma.c
+++ b/drivers/dma/stm32-mdma.c
@@ -224,7 +224,7 @@ struct stm32_mdma_desc {
  	u32 ccr;
  	bool cyclic;
  	u32 count;
-	struct stm32_mdma_desc_node node[];
+	struct stm32_mdma_desc_node node[] __counted_by(count);
struct stm32_mdma_dma_config {
@@ -321,6 +321,7 @@ static struct stm32_mdma_desc *stm32_mdma_alloc_desc(
  	desc = kzalloc(struct_size(desc, node, count), GFP_NOWAIT);
  	if (!desc)
  		return NULL;
+	desc->count = count;
for (i = 0; i < count; i++) {
  		desc->node[i].hwdesc =
@@ -330,8 +331,6 @@ static struct stm32_mdma_desc *stm32_mdma_alloc_desc(
  			goto err;
- desc->count = count;
  	return desc;

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